The sun generates power at approx. 1kjs-1. A solar cooker is a dome-like parabolic mirror that can reflect and focus the light falling on it to one point and is used as a sustainable way of cooking that uses no fuel. If a solar cooker has an area of 1m, how long will it take to boil 1litre=(1kg) of water fom anambient temperature of 20C. Specific heat capacity of water= 4190jKg-1C-1.
In your Physics Book, there must a formula relating the area of something(parabloic mirror here) to the flux of solar energy and to the "specific heat capacity" of a substance. Use that formula and substitute all the variables that you have and you will get your answer. Unfortunately, most of the people here are not physicists, and have forgotten most of the obsecure formulas in physics, which they may not have used for 10, 20 or even 30 years!!.
