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P2 LO: calculate the forces acting on an object Forces between objects When two objects push or pull on each other, they exert equal and opposite forces on one another e.g. you are all pushing down on the floor, but the floor is also pushing up on you….if it didn’t you’d fall straight through the floor! LO: calculate the forces acting on an object Resultant force If you have multiple forces acting on an object, you can replace them with one single force that has the effect of all the other forces combined together. This single force is called the resultant force LO: calculate the forces acting on an object Calculating the resultant A rocket produces a thrust of 2000N. It has a weight of 1000N. What is the resultant force acting on the rocket? LO: calculate the forces acting on an object Calculating the resultant A rocket producing a resultant force of 1000N hits a wall, causing it to come to a stop. What force does the wall exert on the rocket and the rocket exert on the wall. Explain the reasoning for your answer. LO: calculate the forces acting on an object Calculating the resultant A car of weight 5000N produces a driving force of 2000N. It experiences friction force from the ground of 500N and air resistance of 300N. What are the horizontal and vertical resultant forces acting on the car? LO: calculate the forces acting on an object Rules for calculating the resultant 1. Forces that act in the same direction can be added together 2. Forces that act opposite to each other must be taken away 3. Forces that act vertically and horizontally CAN NOT be added and taken away from each other and MUST be considered separately. LO: calculate the forces acting on an object Effects of forces 1 • The resultant force on a stationary (not moving) object is zero! • If a resultant force is applied to an object, it will accelerate in the direction of the force LO: calculate the forces acting on an object Effects of forces 2 • If an object is moving with constant speed, the resultant force on it is zero • If a resultant force is applied to a moving object, it will accelerate in the direction of the force LO: calculate the forces acting on an object Calculating forces F=mxa • F = force (N) • m = mass (kg) • a = acceleration (m/s2) F mxa LO: calculate the forces acting on an object Example 1 A car of mass 400kg is accelerating at 5m/s2. What is the driving force produced by the engine? LO: calculate the forces acting on an object Example 2 A novice skier is being pulled along a horizontal section of a nursery slope. Given that her acceleration of 1.3m/s2 is provided by a force of 70N, calculate her mass. LO: calculate the forces acting on an object Example 3 A man pushes a car with a force of 200N along a straight horizontal road. He manages to accelerate the car by 0.1m/s². Find the mass of the car. LO: understand how to draw and interpret graphs of motion Graphs of motion Graphs of motion are a visual representation of the motion of a body They can either show the change in displacement or change in velocity of an object LO: understand how to draw and interpret graphs of motion Can you draw… Mr R cycles into work. The journey takes him 15 minutes (900s) and is a total distance of 3km (3000m). We will try to represent his journey using a graph… LO: understand how to draw and interpret graphs of motion Can you draw… 1. Mr R cycles to the first traffic light, a distance of 500m away. It takes him 180 seconds to do this. 2. He waits at the traffic lights for 120 seconds while the light is red 3. When the light turns green, he cycles for 2000m without stopping. This takes him 5 minutes to do. 4. After 2000m, Mr R has to stop at another traffic light. He waits for 180 seconds. 5. Realising that he is about to be late, he sprints the last 500m in 120 seconds. LO: understand how to draw and interpret graphs of motion Mini-plenary 1. Usain Bolt ran the 100m race in London 2012 in approximately 9.6 seconds. He ran the first 20m in approximately 2.7 seconds after accelerating and running the final 80m in 6.9 seconds. It took him 20 metres to come to a stop, which he covered in 5 seconds. Draw a distance-time graph to show this journey. 2. Explain what a horizontal line on a distance-time graph represents Extension: What do you think the steepness of a line on a distance-time graph represents? LO: understand how to draw and interpret graphs of motion Using distance-time graphs • • • How steep the line is (the gradient) on a distance-time graph tells you the speed that an object is moving The steeper the line, the faster something is moving Speed is measured in m/s LO: understand how to draw and interpret graphs of motion Calculating the gradient Gradient = Change in y Change in x Gradient = ∆y ∆x Lets have a go at working out the speed that Mr C was travelling at during his journey to school! LO: understand how to draw and interpret graphs of motion One last definition Two cars are travelling on a road in opposite directions. One is travelling east at 20m/s and the other is travelling west at 20m/s. Their speeds are exactly the same. However, their velocity’s are different. What do you think their velocity’s are? Velocity is the speed of an object in a given direction. Two objects can have the same speed, but very different velocities LO: understand how to draw and interpret graphs of motion Can you draw… Mr R has brought himself a slick new ride! He has also moved house and is now living in the leafy suburbs. His journey takes him 1200 seconds, his top speed is 50m/s and his lowest is -30m/s. Let’s plot his journey into school on a velocity-time graph… LO: understand how to draw and interpret graphs of motion Can you draw… 1. 2. 3. 4. 5. 6. Mr R leaves his house. He is happily driving along on country roads at a steady speed of 30m/s for two minutes… D’oh! He’s forgotten his lunch. He turns round and drives back at 30m/s for two minutes. He is at home for 60s. Back on the road, Mr R drives at 30m/s for 300s Now on the motorway, Mr R is able to drive at 50m/s, which he does for 5mins Coming off the motorway, he stops at a traffic light for 120s Realising he is going to be late, he steadily increases his speed for the next 180 seconds from 0 to 50m/s. He arrives JUST on time! LO: understand how to draw and interpret graphs of motion Task 1. What does a horizontal line on a velocity-time graph represent? 2. How do you know if an object has stopped by looking at the velocity-time graph? 3. How can you tell if an object is accelerating using a velocity time graph? 4. Draw the velocity-time graph for the following journey: 0-10s = 50m/s 10-25s = 0m/s 25-50s = 60m/s 50-80s = acceleration to 80m/s LO: understand how to draw and interpret graphs of motion Acceleration Acceleration is the change in speed of a body over a given amount of time LO: understand how to draw and interpret graphs of motion Acceleration Acceleration can be calculated using the following equation: Change in velocity Acceleration = Time taken Final velocity – initial velocity Acceleration = a= v-u t Time taken • • • • a = acceleration (m/s2) v = final velocity (m/s) u = initial velocity (m/s) t = time (s) LO: understand how to draw and interpret graphs of motion Example 1 A car accelerates from a velocity of 10m/s to a velocity of 25m/s in 15 seconds. What is the acceleration of the car? LO: understand how to draw and interpret graphs of motion Example 2 A runner starts at rest and accelerates to a top speed of 10m/s. If he does this in 2 seconds, what is his acceleration? LO: understand how to draw and interpret graphs of motion Example 3 A train accelerates at 2m/s² for 30 seconds. If its initial velocity was 10m/s, calculate what the final velocity will be after 30 seconds. LO: understand how to draw and interpret graphs of motion Task 1. What is the acceleration of a car that starts at rest and reaches a top speed of 50m/s in 25 seconds? 2. A plane starts at rest. It takes 8 seconds to take off and accelerates at a constant rate of 10m/s². What is the final takeoff velocity of the aircraft? 3. A runner starting at rest reaches a speed of 11m/s in 2.2 seconds during the drive phase of his 100m sprint. What is his acceleration during this phase? Assuming that his speed remains constant for the rest of the race, sketch the velocitytime graph for his journey 4. A car accelerates at 5m/s² for 12 seconds, reaching a final velocity of 80m/s. What was the car’s initial velocity before it started accelerating? LO: understand how to draw and interpret graphs of motion How are they linked? Gradient = Change in y Change in x Gradient = ∆y ∆x The gradient of a velocity time graph represent the acceleration of an object! Go back and calculate the acceleration of Mr C in the final part of his journey LO: understand the factors that affect the stopping distance of a car Streamlining Most of the resistance forces that act on a car are due to air resistance. Streamlining a car will increase the top speed, even if the engine is giving the same power output LO: understand the factors that affect the stopping distance of a car Stopping distance The stopping distance of a car is the minimum distance that a car can safely stop in Stopping distance = thinking distance + braking distance LO: understand the factors that affect the stopping distance of a car Thinking distance The thinking distance is the distance travelled by the vehicle in the time it takes for the driver to react alcohol other drugs and some medicines distractions, such as mobile phones tiredness speed LO: understand the factors that affect the stopping distance of a car Stopping distance The stopping distance is the distance travelled by the vehicle during the time the braking force acts weather condition of tyres/brakes condition of road speed LO: understand the factors that affect the stopping distance of a car Typical stopping distances What effect would factors such as drugs, alcohol, tiredness, higher speed, adverse weather, poor road conditions or worn out breaks have on these stopping distances? LO: understand the factors that affect the stopping distance of a car Braking force Which of these would need the bigger force to stop if the stopping distance remained the same? Why? LO: understand the factors that affect the stopping distance of a car QWC Practice A local authority is worried about the number of road deaths occurring in the area. They have imposed a ban on mobile phones while driving, imposed a speed limit of 30mph and installed speed cameras. Explain how the changes may lead to fewer people being hit by cars. 5-6 marks criteria: • Knowledge of accurate information appropriately contextualised • Detailed understanding, supported by relevant evidence and examples • Answer is coherent and in an organised, logical sequence, containing a wide range of appropriate or relevant specialist terms used accurately • The answer shows almost faultless spelling, punctuation and grammar. LO: understand what is meant by terminal velocity What is happening? The graph below shows the velocity-time profile for a skydiver falling through the air. Discuss with the people on your pod what you think is happening and why. Think about the forces that are involved at each stage LO: understand what is meant by terminal velocity Moving in a fluid Let’s think about what happens when an object moves through a fluid by considering a skydiver When the skydiver FIRST jumps out of the aircraft, gravity causes him to accelerate. The acceleration is a constant so the line on v-t graph will have an unchanging steepness at the beginning LO: understand what is meant by terminal velocity Moving in a fluid As the speed of the skydiver increases, the air resistance on him increases. The increased air resistance causes his acceleration to decrease. However, his velocity is still increasing i.e. he’s speeding up slower than before, but he’s NOT slowing down. LO: understand what is meant by terminal velocity Moving in a fluid After a certain amount of time, the weight of the skydiver and the air resistance on the skydiver will be balanced. At this point, the skydiver will be moving at a constant velocity. This is the MAXIMUM velocity it is possible for him to move with and is known as the TERMINAL VELOCITY. LO: understand what is meant by terminal velocity Moving in a fluid The process that we have just considered is relevant for ANY object that is moving in a fluid e.g. a car driving along a road, a plane flying at 2000ft, a submarine underwater etc. LO: understand what is meant by terminal velocity Moving in a fluid The factors that will increase/decrease the terminal velocity of an object are: • The driving force that the object can generate • How streamlined the object is • The fluid that the object is travelling through LO: understand what is meant by terminal velocity Calculating weight The weight of an object is the force that acts on an object due to gravity. It can be calculated using the following equation: W=mxg W = weight (Newtons) M = mass (kg) g = gravitational field strength (N/kg) g has a value of 9.81 on earth LO: understand the link between force and extension of an object Changing shape When a force is applied to an object, it may accelerate. However, a second effect that the force may cause is a change in shape of the object LO: understand the link between force and extension of an object Stretching objects When an object is stretched, it stores elastic potential energy. Some objects are better at storing this energy than others. Which of the materials on your pod is better at storing elastic potential energy? LO: understand the link between force and extension of an object Material properties Beyond a point, the material will start to show plastic behaviour. Beyond the proportional limit, the material shows plastic behaviour. The extension is now much harder to predict A small increase in force will give a large increase in extension. The deformation will be irreversible (the material will not go back to the original shape when the force is taken away) LO: understand the link between force and extension of an object Real world application Knowing how materials change shape under force is essential to most aspects of university. The flexing of aircraft wings can dramatically change the lift generated. It also needs to be within limits to make sure the wings don’t break off! LO: understand the link between force and extension of an object Hooke’s Law Hooke’s law states that: The extension of an object is directly proportional to the force that is applied to it provided that the limit of proportionality is not exceeded LO: understand the link between force and extension of an object Hooke’s Law Hooke’s law can be written as: F=kxe • • • F = Force (N) k = spring constant (N/m) e = extension (m) LO: understand the link between force and extension of an object Task 1. Calculate the spring constant for the spring that you did the experiment with 2. A spring is loaded with a force of 50N four times. The spring shows extensions of 0.23m, 0.25m, 0.25m and 0.24m. Calculate the spring constant for this spring 3. For the spring in the question above, calculate the force when the extension of the spring is 100cm. 4. A second spring is loaded with 100N. It shows an extension of 60cm. What is the difference between the spring constants of the two springs? 5. What would be the force required to extend the second spring by 0.45m? LO: understand how energy can be transferred What is work? An object is said to have done WORK when it transfers (uses) energy LO: understand how energy can be transferred Calculating work The work done by an object is equal to the amount of energy that it transfers Work done = force x distance W=fxd • W = work done(J) • f = force (N) • d = distance(m) LO: understand how energy can be transferred Example 1 An object of weight 40N is raised by a height of 0.4m. Calculate the work done in raising the object. LO: understand how energy can be transferred Example 2 2000J of energy is transferred by a sprinter as he runs a distance of 100m. Calculate the force that is exerted by the sprinter as he is running. LO: understand how energy can be transferred Example Questions 1. What is the definition of work done? 2. What is the unit for energy? 3. The engine of a car exerts a force of 750N. How much energy would be transferred by the engine if the car moved a distance of 100m? 4. An object of weight 50N is raised by a height of 200cm. What is the work done in raising the object? 5. 700J of energy is used by a person to move a distance of 10m. What is the force exerted by the person as they walk the distance? 6. Object A has a weight of 200N. Object B has a weight of 350N. If 1000J of energy is used to raise each object, which object will gain the most height? LO: understand how energy can be transferred Calculating power Power is the amount of work done/energy transferred in a given time Power = work done / time P=W/t • P = power (W) • W = work done (J) • t = time (s) LO: understand how energy can be transferred Example 1 An object of weight 700N is raised by a height of 2m in a time of four seconds. Calculate the work done in raising the object and the power. LO: understand how energy can be transferred Example Questions 1. A car engine transfers 3000J in 20 seconds. What is the power generated by the engine? 2. 400J of energy is transferred in raising an object in 1 minute. What is the power? 3. A kettle has a power rating of 2000W. How much work is done by the kettle in boiling water in 40 seconds? 4. A student of weight 500N transfers 2000J whilst running up some stairs. She reaches the top of the stairs in 3 seconds. How high are the stairs and what is her power? 5. A sprinter can generate 150W whilst running. If he transfers 450J of energy, how long has he been running for? LO: understand the nature of gravitational potential energy Gravitational Potential Energy Any object that is raised above the ground will have gravitational potential energy LO: understand the nature of gravitational potential energy Gravitational Potential Energy GPE = mass x Gravitational x height Field strength GPE = m x g x h • • • • GPE = gravitational potential energy (J) m = mass (kg) g = gravitational field strength (N/kg) h = height (m) LO: understand the nature of gravitational potential energy Example 1 An object of mass 10kg is raised by a height of 20m. What is the gravitational potential energy of the object? LO: understand the nature of gravitational potential energy Example 2 An object gains gravitational potential energy of 300J. If the mass of the object is 3kg, what is the height that the object has been raised? LO: understand the nature of kinetic energy Kinetic energy All objects that are moving have kinetic energy! LO: understand the nature of kinetic energy Kinetic energy KE = ½ x m x v² • • • KE = kinetic energy (J) m = mass (kg) v = velocity (m/s) LO: understand the nature of kinetic energy Example 1 An object has a mass of 2kg and is moving with a velocity of 5m/s. What is the kinetic energy of the object? LO: understand the nature of kinetic energy Example 2 An object of mass 300g has 600J of kinetic energy. How fast is the object moving? LO: understand the nature of kinetic energy Example questions 1. What is the equation that is used to calculate the kinetic energy of an object? 2. Calculate the kinetic energy of an object of mass 500g that is moving with a velocity of 20m/s 3. A car of mass 500kg is a moving with a velocity of 10m/s. It accelerates to a velocity of 15m/s. What is the KE of the object before and after it accelerates? 4. A sprinter has kinetic energy of 1000J and a mass of 68kg. How fast is the sprinter running? 5. A ball of mass of 0.5kg is dropped from a height of 2m. Assuming that all of the GPE is transferred to KE, what will be the velocity of the ball when it hits the ground? LO: understand what is meant by momentum Momentum ALL MOVING OBJECTS HAVE MOMENTUM! LO: understand what is meant by momentum Momentum P=mxv • P = momentum (kgm/s) • m = mass (kg) • v = velocity (m/s) LO: understand what is meant by momentum Example question 1 An object of mass 300g is moving with velocity of 5m/s. What is its momentum? LO: understand what is meant by momentum Example question 2 An object has momentum of 50kgm/s. If the object has a mass of 25kg, what is its velocity? LO: understand what is meant by momentum Example questions 1. What is the momentum of a bullet of mass 50g travelling at 300 m/s? 2. What is the momentum of a dog (mass 12 kg) fired out of a canon at 120 m/s? 3. Calculate the momentum of a 65 kg sprinter when travelling at 9.5 ms-1. 4. Calculate the velocity of a car of mass 700 kg that has the same momentum as the sprinter in Q3 5. A body has a mass of 2.5 kg. Calculate: • Its momentum when it has a velocity of 3.0 m/s • Its velocity when it has a momentum of 10.0 kgm/s LO: understand what is meant by momentum Conservation of momentum In a closed system, the total momentum before an event and the total momentum after an event are the same. This is called conservation of momentum. Events you may be asked about in your exams are: • Collisions • Explosions LO: understand what is meant by momentum Example 1 A railway engine of mass 800kg travelling at 5m/s collides with and becomes attached to a truck of mass 200kg travelling at 2m/s. Calculate the speed of the truck and engine after the collision LO: understand what is meant by momentum Example 2 A 0.5kg trolley is pushed at a velocity of 1.2m/s into a stationary trolley of mass 1.5kg. The two trolleys stick to each other after the impact. Calculate: • The momentum of the 0.5kg trolley before the collision • The velocity of the two trolleys straight after the impact LO: explain how safety features on a car work Brakes and crumple zones Brakes and crumple zones are two of the main safety features on a car LO: explain how safety features on a car work Brakes and crumple zones Both features work by transferring kinetic energy into other forms. What energy transfers take place in each of these features? LO: understand static electricity Structure of an atom All matter is made up of atoms However, an atoms is NOT the smallest unit of matter like you might have been previously taught Atoms of themselves made of smaller particles LO: understand static electricity What is an atom made up of? Protons – Positively charged particles found inside the nucleus Neutrons – Neutral particles found inside the nucleus Electrons – Negatively charged particles that orbit the nucleus LO: understand static electricity Static electricity by friction When you rub one of the rods with the cloths, you create static electricity. This happens in one of two ways. For the polythene rod, the dry cloth transfers electrons TO the surface of the rod and gives it a negative charge LO: understand static electricity Static electricity by friction When you rub one of the rods with the cloths, you create static electricity. This happens in one of two ways. For the perspex rod, the dry cloth transfers electrons away from the surface of the rod. This gives it a positive charge LO: understand static electricity Static electricity rules 1. Like (The same) charges attract 2. Unlike (The opposite) charges repel LO: Understand how to create electrical circuits Key definitions When considering electricity, we will usually use three key terms: 1) Current: This is the flow of electric charges around a circuit. The size of the current is dependent on the rate of flow of electric charges 2) Potential Difference (Voltage): The potential difference between two points is the work done per unit charge between two points 3) Resistance: This is the resistance to the flow of electrons around a circuit LO: Understand how to create electrical circuits Calculating current I = Q/t • I = Current (Amps, A) • Q = Charge (Coulombs, c) • t = Time (s) LO: Understand how to create electrical circuits Example question 1 Calculate the current when 4C passes a point in 8 seconds LO: Understand how to create electrical circuits Example question 2 An ammeter is records a current of 8A. Calculate how much charge is passing through the ammeter in 10 seconds. LO: Understand how to create electrical circuits Task 1. What is the current when 20C of charge pass through an ammeter in 2minutes? 2. A battery can produce 20A of current. How much charge does it discharge in 30s? 3. Another battery can produce a charge of 30A. How long will this battery be running before it has discharge the same amount of charge as the battery in Q2? 4. A car engine requires a battery that can produce a current of 40A to start. A mechanic places a battery that can discharge 100C in 30s into a car. Will this battery be good enough to start the car? Why? 5. For the question above, how much charge would the battery have to discharge in 30s to start the engine? LO: Understand how to create electrical circuits Calculating voltage V = W/Q • V = Voltage (Volts, V) • W = Work done (Joules, J) • Q = Charge (Coulombs, c) LO: Understand how to create electrical circuits Example question 1 A battery transfers 30J for every coulomb of charge that passes through the battery. What is the potential difference of the battery? LO: Understand how to create electrical circuits Example question 2 A battery has a voltage rating of 40V. How much energy is transferred by the battery if 20C of charge pass through the battery? LO: Understand how to create electrical circuits Task 1. What is the voltage of a battery if it transfers 40J of energy for every 10C that pass through it? 2. A builder requires a 400V battery to power his pneumatic drill. He is told that a battery transfers 1000J for every 3C of charge that pass through it. Will this battery be good enough? Why? 3. How much energy would the battery in the question above need to transfer for every 3C to have a voltage of 400V? 4. Battery A has a rating of 300V. Battery B has a rating of 500V. What is the difference in the amount of work done by the two batteries if 20C of charge pass through both batteries? LO: Understand how to create electrical circuits Circuit symbols LO: Understand the relationship-between current and voltage in a circuit Ohm’s Law Ohm’s Law states that the current through a resistor is proportional to the potential difference provided the temperature is constant LO: Understand the relationship-between current and voltage in a circuit Ohm’s Law V = IR • V = Voltage (V) • I = Current (A) • R = Resistance (Ohms, Ω) LO: Understand the relationship-between current and voltage in a circuit Ohm’s Law 1 Calculate the potential difference across a 4Ω resistor when the current through it is 10A. LO: Understand the relationship-between current and voltage in a circuit Ohm’s Law 2 The potential difference across a 30Ω is 20V. What is the current through the resistor? LO: Understand the relationship-between current and voltage in a circuit Task Calculate: 1. The resistance of a bulb if the current is 0.5 A and the potential difference across the bulb is 2 V. 2. The potential difference across a bulb if the resistance of the bulb is 3 and the current flowing is 2 A 3. The potential difference across a resistor of 5 with a current of 1.5 A. 4. The total resistance of a circuit if the potential difference across the cell is 12V and the current is 3 A. 5. The current flowing in a circuit with a total resistance of 5 and a potential difference across the cell of 6V. LO: Understand the relationship-between current and voltage in a circuit Non-Ohmic Components1 An LED does not follow Ohm’s law and is designed to only allow current to flow through in one direction LO: Understand the relationship-between current and voltage in a circuit Non-Ohmic Components2 An LED does not follow Ohm’s law and will only light up when current to flows through in the right direction. If current tries to flow in the other direction it encounters a MAHOOSIVE resistance! LO: Understand the relationship-between current and voltage in a circuit Non-Ohmic Components2 An LDR is a component whose resistance decreases as the light intensity that falls on it increases Where would this be useful? LO: Understand the relationship-between current and voltage in a circuit Non-Ohmic Components3 A thermistor is a component whose resistance decreases when the temperature increases. Where would this be useful? LO: describe features of mains electricity AC vs DC If you turn on any battery powered device the electricity will only ever flow in one direction. This is called DIRECT CURRRENT (d.c.) as the electricity goes around in just one direction. LO: describe features of mains electricity AC vs DC However, the same isn’t true for mains electricity. Mains electricity uses ALTERNATING CURRENT (a.c.) which repeatedly flows in one direction and then reverses its flow. The frequency is how many times it changes direction in one second LO: describe features of mains electricity Key points 1. Mains electricity uses a.c. 2. Mains electricity is at 230V 3. Mains electricity has a frequency of 50Hz. This means it changes direction 50 times in one second LO: describe features of mains electricity Cables and Plugs Cables and wires are designed to allow people to use them without risk of hurting themselves. Most appliances are supplied with three-core cable. This means the cable is made up of three separate wires. LO: describe features of mains electricity Components of a plug and cable 1) Live wire (brown) – This carries the current to the appliance. Touching this can be deadly! 2) Neutral wire (blue) – This completes the circuit and is usually at 0V 3) Earth wire (green/yellow) – This ‘earths’ the appliance in case one of the wires touches the casing 4) Fuse – This stops the flow of current if it gets too high LO: describe features of mains electricity Earthing Components are earthed to make sure you don’t get an electric shock if the live wire accidentally touches the casing. The electricity will flow harmlessly through the earth wire instead of through you when you touch the casing. However, appliances with plastic cases (hairdryers etc.) don’t have earth wires. Why is this? LO: describe features of mains electricity Earthing Plastic is an insulator, so there is no danger if the live wire touches the casing. Therefore, these appliances are supplied with twocore cables instead of three-core cables i.e. they don’t have earth wires because they don’t need them LO: describe features of mains electricity Fuses A fuse is a component that has a wire running through it made of a different material/thickness than the rest of the circuit. It is designed to stop current that is too high flowing through it. LO: describe features of mains electricity Fuses Fuses have a rating based on the amount of current they will allow through. For example, a 13A fuse will allow a maximum of 13 amps of current to flow through. If MORE than this tries to flow through, the wire heats up and melts, breaking the circuit and protecting the appliance LO: describe features of mains electricity Circuit Breakers Circuit breakers are fitted in newer homes. They measure the difference in current in the live and neutral wires. If the difference is too great, an electromagnetic switch opens (‘trips’) which stops the flow of current. They work a lot faster than fuses and can be reset easily LO: describe features of mains electricity Circuit Breakers Use the textbook spread to create a poster on fuses and circuit breakers. Your poster to include details of how they work and advantages and disadvantages of both LO: describe features of mains electricity Knowledge check Copy the true sentences and change the false sentences to make them true: 1. The earth wire in a three-core cable is usually brown 2. Appliances with metal casings are supplied with threecore cables 3. Fuses stop current flowing through a circuit by melting when the current flowing through them is above a certain value 4. A circuit breaker works by monitoring the difference in current between the live and earth wire 5. Mains electricity uses direct current at 100Hz. LO: describe features of mains electricity QWC Practice Using as much detail as possible, explain how fuses and circuit breakers work to protect people and appliances. Which, in your opinion, is the better choice for installation into a home and why? 5-6 marks criteria: • Knowledge of accurate information appropriately contextualised • Detailed understanding, supported by relevant evidence and examples • Answer is coherent and in an organised, logical sequence, containing a wide range of appropriate or relevant specialist terms used accurately • The answer shows almost faultless spelling, punctuation and grammar. LO: describe features of mains electricity Calculating power P=VxI • P = Power (w) • V = Voltage (V) • I = Current (A) LO: describe features of mains electricity Example 1 Calculate the power of a bulb if it is supplied with a potential difference of 230V and the current flowing through it is 0.4A LO: describe features of mains electricity Example 2 A kettle has a power rating of 1000W. If it is supplied with a potential difference of 230V, what is the current flowing through it? LO: describe features of mains electricity Example questions 1. A light bulb is connected to a 2V supply and experiences a current of 6.4A. What is the power rating of the bulb? 2. A kettle has a power rating of 1500w. What is the potential difference that it must be supplied with to have a current flowing through it of 30A? 3. A student attaches a 10V supply to a bulb with a power rating of 100w. What is the current running through the bulb? 4. The student now connect a 25w bulb to the same supply. What is the difference between the current going through this bulb compared to the 100w bulb? 5. Bulb A transfers 1000J in 10seconds. Bulb B transfers 1500J in 3 seconds. Which bulb will have a higher current running through it when connected to a 12V supply? LO: Understand how to create electrical circuits Calculating energy E=VxQ • E = Energy transferred (Joules, J) • V = Voltage (Volts, V) • Q = Charge (Coulombs, c) LO: Understand how to create electrical circuits Example question 1 A battery transfers 30J for every coulomb of charge that passes through the battery. What is the potential difference of the battery? LO: Understand how to create electrical circuits Example question 2 A battery has a voltage rating of 40V. How much energy is transferred by the battery if 20C of charge pass through the battery? LO: Understand how to create electrical circuits Task 1. What is the voltage of a battery if it transfers 40J of energy for every 10C that pass through it? 2. A builder requires a 400V battery to power his pneumatic drill. He is told that a battery transfers 1000J for every 3C of charge that pass through it. Will this battery be good enough? Why? 3. How much energy would the battery in the question above need to transfer for every 3C to have a voltage of 400V? 4. Battery A has a rating of 300V. Battery B has a rating of 500V. What is the difference in the amount of work done by the two batteries if 20C of charge pass through both batteries? LO: understand the nature of radioactive decay What is an atom made up of? Protons – Positively charged particles found inside the nucleus Neutrons – Neutral particles found inside the nucleus Electrons – Negatively charged particles that orbit the nucleus LO: understand the nature of radioactive decay Protons, neutrons and electrons Particle Proton Neutron Electron Relative charge +1 0 -1 Relative mass 1 1 1/2000 LO: understand the nature of radioactive decay Relative sizes LO: understand the nature of radioactive decay Atomic and Mass number Atomic number: This is the number of protons inside the nucleus of an atom WARNING: Even though the number of protons and electrons in a neutral atom are the same, make sure you say the correct definitions if you are asked in an exam! Mass number: This is the number of protons + neutrons in the nucleus of an atom LO: understand the nature of radioactive decay Atomic and Mass number Atomic number: This is the number of protons inside the nucleus of an atom Mass number: This is the number of protons + neutrons in the nucleus of an atom LO: understand the nature of radioactive decay Example 1 Calculate the following quantities for the element below (i) Atomic number (ii) Mass number (iii) Number of protons (iv) Number of electrons (v) Number of neutrons LO: understand the nature of radioactive decay Example 2 Calculate the following quantities for the element below (i) Atomic number (ii) Mass number (iii) Number of protons LO: understand the nature of radioactive decay Task Use your periodic table to find the following quantities for: nitrogen, oxygen, iron, platinum, gold, lead, mercury, potassium, calcium, phosphorus, argon, xenon (i) Atomic number (ii) Mass number (iii) Number of protons (iv) Number of electrons (v) Number of neutrons If the numbers are decimals, round them to the nearest whole number LO: understand the nature of radioactive decay The Plum Pudding Model - 1897 LO: understand the nature of radioactive decay Enter Rutherford Ernest Rutherford fired alpha particles at gold foil. Alpha particles have a positive charge and he expected them to go through the particle, with a small amount of deviation from their path LO: understand the nature of radioactive decay Gold Foil Experiment - 1911 The results are very different! Most alpha particles go straight through with no deviation! Some, however, are diverted through very large angles! The physics community is flummoxed by this finding! LO: understand the nature of radioactive decay Gold Foil Experiment - 1911 The results are very different! Most alpha particles go straight through with no deviation! Some, however, are diverted through very large angles! The physics community is flummoxed by this finding! LO: understand the nature of radioactive decay Conclusions Most of the fast, highly charged alpha particles went whizzing straight through undeflected. SUGGESTS THAT MOST OF THE ATOM IS EMPTY SPACE!! LO: understand the nature of radioactive decay Conclusions Some of the alpha particles were deflected back through large angles. A very small number of alpha particles were deflected backwards! SUGGESTS THAT THERE IS A CONCENTRATED POSITIVE MASS SOMEWHERE IN THE ATOM. LO: understand the nature of radioactive decay Conclusions A very small number of alpha particles were deflected backwards! SUGGESTS THAT THE CONCENTRATED MASS IS MINISCULE COMPARED TO THE SIZE OF THE REST OF THE ATOM, BUT CONTAINS MOST OF THE MASS LO: understand the nature of radioactive decay Types of Radiation There are three different kinds of radiation. Each one has a unique nature and penetration Alpha radiation: This particle is made up of two protons and two neutrons (i.e. a Helium nucleus). It has a charge of +2 and moves slowly because of it’s large mass. It can be stopped by a few cm of air or by a piece of paper LO: understand the nature of radioactive decay Types of Radiation There are three different kinds of radiation. Each one has a unique nature and penetration Beta radiation: During beta radiation, a neutron turns into a proton inside the nucleus and gives off an electron, which is fired from the nucleus. The electron is small and light and so moves very fast! Beta particles can be stopped by a thin sheet of aluminium LO: understand the nature of radioactive decay Types of Radiation There are three different kinds of radiation. Each one has a unique nature and penetration Gamma radiation: Gamma radiation usually follows alpha or beta decay. It is NOT a particle like the other two. It is a high energy EM wave that travels at the speed of light (the fastest that anything can travel Joel). It can only be stopped by a very thick piece of lead or concrete. LO: understand the nature of fusion and fission Isotopes The diagram below shows three isotopes of hydrogen. What is the same and different for each isotope of hydrogen? LO: understand the nature of fusion and fission Isotopes An isotope of an element has the same number of protons and neutrons as the original, but a different number of neutrons. LO: understand the nature of fusion and fission Radioactivity of a substance LO: understand the nature of fusion and fission Radioactivity of a substance As a radioactive substance decays, the number of particles left in it will start to reduce. Therefore the radioactivity of the substance will begin to decrease. It will continue to decrease, until the radioactivity has reached zero! LO: understand the nature of fusion and fission Half-life The half-life of a substance is the time it takes for HALF of the particles in a sample to decay or for the radioactivity of a substance to decrease by HALF. LO: understand the nature of fusion and fission Half-life What is the half life of this substance? LO: understand the nature of fusion and fission Recap Particle Charge Proton +1 Neutron 0 Electron -1 In each atom, the number of protons will ALWAYS be the same as the number of electrons. This makes sure that the overall charge is zero. LO: understand the nature of fusion and fission Nuclear Fission Nuclear fission is a process that uses atoms to generate VAST amounts of energy. LO: understand the nature of fusion and fission Nuclear Fission To begin with, we have a simple Uranium nucleus. Uranium is used because it is already unstable. A slow moving neutron is fired at the Uranium. Neutron Uranium nucleus LO: understand the nature of fusion and fission Nuclear Fission Neutron Unstable nucleus Uranium nucleus The neutron attaches itself to the uranium and makes it even more unstable! LO: understand the nature of fusion and fission Nuclear Fission The unstable Uranium splits into two smaller nuclei, releasing energy in the process Neutron Unstable nucleus Uranium nucleus 2 smaller nuclei (e.g. barium and krypton) LO: understand the nature of fusion and fission Nuclear Fission Along with the energy, some more neutrons are also released! Neutron Unstable nucleus Uranium nucleus 2 smaller nuclei (e.g. barium and krypton) More neutrons LO: understand the nature of fusion and fission Chain reactions These fission reactions produce a lot of energy and are used in nuclear generators. However, each fission reaction produces more and more neutrons. More neutrons LO: understand the nature of fusion and fission Chain reactions Each of the neutrons can cause more fission reactions, releasing more energy and more neutrons. The reaction can soon become an uncontrollable chain reaction, and when that happens… More neutrons LO: understand the nature of fusion and fission Using fission LO: understand the nature of fusion and fission True or False? Copy the true sentences and change the false sentences to make them true 1) Nuclear fission uses fast-moving electrons 2) The most common fuel used in a nuclear reactor is uranium 3) Nuclear fission involves one nucleus splitting into smaller nuclei and releasing energy in the process 4) An advantage of nuclear fission is that it doesn’t produce any harmful radioactive waste 5) A chain reaction occurs when too many neutrons cause fission reactions and the process can no longer be controlled LO: understand the nature of fusion and fission Nuclear fusion Although the names sound very similar, fission and fusion are VERY DIFFERENT PROCESSES. LO: understand the nature of fusion and fission Nuclear Fission In fission, one nuclei is split into smaller nuclei to release energy! Neutron Unstable nucleus Uranium nucleus 2 smaller nuclei (e.g. barium and krypton) More neutrons LO: understand the nature of fusion and fission Nuclear fusion In nuclear fusion, two nuclei are fused together to release energy. It is the opposite of nuclear fission. LO: understand the nature of fusion and fission Where does this happen? Contrary to popular belief, our sun is not a massive fireball. It is actually a massive fusion reactor! LO: understand the nature of fusion and fission Where does this happen? The sun is made up of mainly hydrogen. The high temperature on the sun allows the hydrogen to fuse together and make helium, releasing massive amounts of energy in the process LO: understand the nature of fusion and fission Why don’t we use fusion? Fusion seems like a great process! We only need hydrogen to do it (which we can get from water) and make helium, which is not a greenhouse gas…so why are we not using it? LO: understand the nature of fusion and fission Fusion future Although fusion isn’t economically viable right now, it will (probably!) be one of the main ways we generate energy in the future. Lots and lots of research is currently being done into it currently…. LO: understand the lifecycle of a star Nebula All stars start their lives as part of a nebula. Nebulae are large clouds of dust and gas (mainly hydrogen). LO: understand the lifecycle of a star Protostar Over millions of years, gravity will cause the dust and gas in the nebula to come together. As it does this, the temperature increases until hydrogen can fuse. When this happens, a protostar is born. This is kind of like a ‘baby’ star. LO: understand the lifecycle of a star Main sequence star The main sequence star is the next stage after a protostar. Hydrogen fusion is now in full flow and the star is much hotter and brighter than the protostar. LO: understand the lifecycle of a star Red Giant star When a star runs out of hydrogen, it begins to fuse other, heavier elements. This releases more energy, causing the star to expand. It also gives off red light, giving it the name ‘Red Giant’. LO: understand the lifecycle of a star White dwarf When the red giant has run out of all fuel and can fuse nothing more, it will lose its outer layers. This leaves just the core, which is still extremely hot. It is so hot it glows white hot, giving the name to this stage – the ‘white dwarf’. LO: understand the lifecycle of a star Black dwarf After a long enough time, the white dwarf will cool down enough so that it stops glowing white hot. It is now called a ‘black dwarf’. LO: understand the lifecycle of a star Task The lifecycle that you have just covered is for stars about the same mass as our sun…Heavier stars, however, lead a slightly different life LO: understand the lifecycle of a star Red Super Giant star Following the main sequence, the star begins to fuse together heavier elements. However, as it has far more fuel, it expands to a much larger size and gives off much more energy. LO: understand the lifecycle of a star Supernova For very heavy stars, once they have run out of fuel, the star begins to collapse in on itself. It continues to collapse until it reaches a critical point when it can’t collapse any more. This causes a MASSIVE shockwave! LO: understand the lifecycle of a star Supernova The shockwave is so large that the outer layers EXPLODE outwards! The explosion only lasts seconds, but can release as much energy in those seconds as the star has released up to that point! It can be as bright as the light from 10billion stars. LO: understand the lifecycle of a star Neutron star After a supernova, only the star’s core is left behind. During the collapsing process, this core is turned into just neutrons. The resulting ‘neutron star’ is very very dense. One spoonful of a neutron star would weigh more than the Earth! LO: understand the lifecycle of a star Black hole In some very very rare cases, the core of a star left over after a supernova will continue to collapse. It will keep getting smaller and smaller until the whole star has collapsed into an infinitely small point. LO: understand the lifecycle of a star Black hole This ‘singularity’ has an immense gravitational force. It’s attraction is so strong that not even light can escape from it. Hence the name ‘black hole’. LO: understand the lifecycle of a star How elements are formed Stars are the perfect place for elements to be made! They are like massive ovens that have the energy needed to make new elements LO: understand the lifecycle of a star Stage 1 When a star is ‘young’ it has plenty of hydrogen. It fuses the hydrogen together to form helium. This releases massive amounts of energy in the form of light and heat. But what happens when the hydrogen runs out? LO: understand the lifecycle of a star Stage 2 When a star runs out of hydrogen, it has massive amounts of helium left. It has no choice but to start fusing helium, instead of hydrogen. Fusing helium makes heavier elements, like lithium and beryllium. LO: understand the lifecycle of a star Stage 2 Fusing helium releases more energy than fusing hydrogen. This makes the star bigger and it enters the red giant phase. But what does it do when it runs out of helium? LO: understand the lifecycle of a star Stage 3 When the star has run out of helium, it will start fusing the heavier elements that it has created. This will make even heavier elements, such as Boron and Carbon. LO: understand the lifecycle of a star Stage 4 The star will keep on going through this process of running out of fuel and fusing heavy elements that it has created. This will make heavier and heavier elements. The heaviest element that stars can make is Iron. LO: understand the lifecycle of a star What about elements heavier than Iron? LO: understand the lifecycle of a star Supernova The temperature in stars is not hot enough to make elements heavier than Iron. For these temperatures, a supernova is required!