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Electricity (problem solving) Prepared by: Edward A. Mirador San Bartolome High School 1. How much electrical energy is used up in 2 hours by a 220 V electric stove whose power rating is 3 kW? A – 3 kWh B – 6 kWh C – 440 kWh D – 660 kWh Correct ! E=Pxt Congratulations 2. What is the total amount of electrical energy consumed by three 100W lamps and five 50W lamps if these are used for 30 days at an average of five hours daily? A – 0.825 kWh B – 8.25 kWh C – 82.5 kWh D – 825.0 kWh Correct ! E=Pxt 300W x 150h = 45kW 250W x 150h = 37.5kW + 82.5kW Congratulations 3. How much current is in the filament of a 100 W lamp connected to a 220 V line? A – 0.45 A B – 2.2 A C – 4.5 A D – 22.0 A Correct ! I=P/V Congratulations 4. An electric meter showed an increase in reading of 8 kWh after a flat iron was used. About how many hours was it used if it carried a 5 A current from a 220 V line? A–1 B–4 C–7 D – 40 Correct ! P=VxI t =E/P Congratulations 5. Fifty identical Christmas lights are connected in series and plugged into a 220V line. Neglecting wire resistance, what is the voltage across each bulb? A – 2.2 V B – 4.4 V C – 110 V D – 220 V Correct ! . Vtotal = V1 + V2 + V3+…+ Vn n = number of loads Since R is identical so as the V across Therefore V = Vtotal / n Congratulations 6. Which of the following correctly ranks the equivalent resistance of the three 100 resistors arranged as shown below from greatest to least value?? A – 2-1-4-3 B – 2-3-1-4 C – 2-3-4-1 D – 2-4-1-3 Correct ! . 1. RT = 1/3 R 2. RT = 3 R 3. RT = 3/2 R 4. RT = 2/3 R Congratulations Sorry That was the wrong answer