B B A

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.

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.

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 - 48 J ) = 52J 52 J x 100% = 52 % energy wasted 100 J