Some teachers used the word efficient in the everyday sense but were aware of this. For
T21, quick meant efficient and convenient as applied to heating the room quickly, the car
going from A-B most reliably and the kettle boiling water quickly. She only barely
recognised that heat from a filament bulb was scientifically classed as inefficiency.

T23 knew about efficiency in terms of transformations very well. However she equated
the word ‘efficient’ with ‘effective’. T6 countered in that ‘effective’ was an everyday term
and not technically related to ‘efficient’. However, he said that if a statement used the
word ‘efficient’ inappropriately, replacement with the word ‘effective’ could retain
meaning. E.g. with Q13:
A fan heater is efficient because it heats the room up quickly
becomes
A fan heater is effective because it heats the room up quickly.
6.5.3. Discussion
One possible barrier to obtaining reliable knowledge about participants’ understandings of
energy efficiency is the PSTS statements themselves. A number of teachers criticised them
for being bad statements, sometimes meaningless. T7 would not answer Q13 on grounds
that she had no data to make a judgment. The same applied to T2 on Q13, Q15 and Q39.
Q15, on heating with an open window was considered especially unanswerable due to the
fact that in a steady state, energy in equals energy out.
Q13. A fan heater is efficient because it heats the room up quickly.
Q15. If the window is left open, the heating of the room will be less
efficient.
Q39. The brighter torch must be more efficient.

However, a counter argument to this is that by being vague, open or scientifically
contemptuous, the statements and situations do well in testing participants’ application of
their knowledge in new situations. This study showed that it did not necessarily follow
that if a participant was able to iterate the equation for efficiency, that they could
necessarily apply this knowledge.

Most, but not all teachers were able to reiterate the equation for energy efficiency as
energy out compared to energy in. However, a surprising number of teachers still chose to
revert to using the concept in the everyday meaning of ‘quick.’ At least one teacher knew
the physics meaning for efficiency but chose to let pupils use a vernacular meaning as
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