The Sun delivers roughly 1 kW m -2
of power to the
Earth's surface. A parabolic mirror with a 1 m radius is used
to focus this energy onto a beaker containing 1 L of water.
Estimate the time taken by the mirror to raise the temperature of the
water by 50°C, assuming the specific heat capacity of water
to be 4200 J K-kg- and ignoring energy
losses to the surroundings.