### Science Revision QWC writing to evaluate

```Gaining QWC*
marks in Science
*quality of written communication
Writing for different purposes.
The sorts of questions
•
Evaluate, in terms of cost and energy efficiency, the use of
two types of light bulb.
•
Suggest an explanation for the development of these
different species.
•
Use information from the article to discuss the arguments
for and against allowing doctors to experiment with
human fertilisation techniques.
Writing for different purposes
• To Evaluate – to weigh up evidence in order
to reach a judgement
• To explain – to offer reasons how or why
• To discuss – to explore and compare different
ideas
Writing to evaluate
Question from a past paper
The table gives data about two types of light bulb people
may use in their homes.
Types of light bulb
Energy
efficiency
Cost of one light
bulb
in hours
Halogen
10%
£1.95
2,000
Light Emitting Diode
(LED)
32%
£11.70
36,000
Both types of light bulb produce the same amount of
light.
Evaluate, in terms of cost and energy efficiency, the use
of the two types of light bulb.
Evaluate, in terms of cost and energy
efficiency, the use of the two types of
light bulb.
So what do you need to do?
• Compare the cost in detail. (Use evidence and,
if necessary, some calculation.)
• Compare the energy efficiency in detail. (Use
evidence and, if necessary, some calculation.)
• Use these comparisons to support a
conclusion – which is best and why.
Evaluate, in terms of cost and energy
efficiency, the use of the two types of
light bulb.
Five minutes to prepare ideas for an answer.
Remember to cover ALL that is underlined.
Looking at the data:
Cost:
• 1 halogen bulb is cheaper to buy
• 6 halogen lamps cost the same as one LED
• LEDs last longer
• Need to buy 18 more halogen lamps to last the same time as one LED
• 18 halogens cost £35.10
• Costs more to run a halogen than LED
• LED has lower maintenance cost (where many used, eg large department
store lighting)
Energy efficiency:
• LED wastes less energy
• LEDs are more efficient
• LED is 22% more energy efficient
• LED requires smaller input (power) for same output (power)
• LED produces less heat (applying prior knowledge)
• LED works using a smaller current (applying prior knowledge)
Which answer is better – and WHY?
The halogen only costs £1.95,
which is cheaper than the LED
bulb which costs £11.70, but the
LED bulb is more efficient and
lasts 18 times as long as the
halogen does. In the short term,
the halogen bulb is cheaper but
you would have to buy 18 halogen
bulbs in the space of 36,000
would cost £35.10 whereas you
would only need to buy 1 LED
bulb in the space of 36,000 hours
which is £22.40 cheaper than
using halogen bulbs for 36,000
hours.
1
The halogen light bulb is 22% less
energy efficient than the LED light
bulb. Moreover, it does not last as
long. If halogen bulbs were to run
for 36,000 hours – the lifetime of
one LED – 18 bulbs would have to be
bought altogether.
Although one LED, costing £11.70, is
more expensive than a single £1.95
halogen bulb, the 18 that would be
necessary to make halogen last as
long as one LED would cost £35.00.
This is £23.30 more expensive.
Overall, the LED light bulb is the best
because it last 18 times longer, is
more efficient and ultimately costs
less money.
2
Which answer is better – and WHY?
The halogen only costs £1.95,
which is cheaper than the LED
bulb which costs £11.70, but
the LED bulb is more efficient
and lasts 18 times as long as
the halogen does. In the short
term, the halogen bulb is
cheaper but you would have to
buy 18 halogen bulbs in the
18 halogen bulbs would cost
£35.10 whereas you would only
need to buy 1 LED bulb in the
space of 36,000 hours which is
£22.40 cheaper than using
halogen bulbs for 36,000 hours.
1
efficiency, need to know how it
is more efficient.
Clear analysis of cost in
but waffly and repetitive.
No clear statement of best
bulb at the end.
4/6
Which answer is better – and WHY?
The halogen light bulb is 22% less
energy efficient than the LED light
bulb. Moreover, it does not last as
long. If halogen bulbs were to run
for 36,000 hours – the lifetime of
one LED – 18 bulbs would have to be
bought altogether.
Although one LED, costing £11.70, is
more expensive than a single £1.95
halogen bulb, the 18 that would be
necessary to make halogen last as
long as one LED would cost £35.00.
This is £23.30 more expensive.
Overall, the LED light bulb is the
best because it last 18 times longer,
is more efficient and ultimately costs
less money.
2
Calculation of efficiency is detailed
comparison.
Connectives make comparisons