3. B B A

4. 2 a & b.
The spring is a store of elastic PE which when unwinding, transfers energy to its Kinetic
energy store which then turns a small electric generator.
The electric current in the wires is transferred to the thermal energy store of the
surroundings ( slightly) by vibrating the air particles as sound waves.
2 c
Advantage of a clockwork radio:
A clock radio does not need mains electricity or batteries so it is very useful in remote areas.
Disadvantage of a clockwork radio:
A clock radio has to be wound up every time its store of energy has been transferred.

5. 3 a
The current in the wires raises the kinetic energy store and thermal energy store of the
water which is used to clean the dishes. b
After cleaning the dishes, thermal energy is transferred to the surroundings as the
hot water is pumped out . A very small amount of thermal energy is transferred to the
surroundings by sound waves.

6. a. Charging the battery
Energy supplied is, for example 100 J ;
then only 80% of 100J = 80 J is received by the battery
Using the laptop
Energy supplied from the battery is 80 J ;
then only 60% of 80 J = 48 J is usefully used by the laptop
b Energy wasted = Energy I/p - Energy o/p
1 a Energy wasted = ( 100 J J ) = J
52 J x 100% = % energy wasted
100 J