1.  A lamp has a power of 60 watts. It gives out light at a rate of 6 watts.

         a)  The amount of energy supplied to the lamp each second in joules is 60 J.

         b)  The amount of energy transferred usefully as light each second in joules is 6 J.

         c)  The amount of energy wasted each second in joules is 54 J.

         d)  The efficiency of the lamp is:

              Efficiency = (useful energy transferred ÷ total energy input) x 100 %

              Efficiency = (6 ÷ 60) x 100 %

              Efficiency = 10 %

    2.  The following diagram is about a radio.

         a)  The useful energies are light and sound.

         b)  The wasted energy is heat.

         c)  The efficiency of the radio is:

              Efficiency = (useful energy transferred ÷ total energy input) x 100 %

              Efficiency = (350 ÷ 500) x 100 %