Question

An experiment needs to heat a small sample to temperature $900K$, but the only available large object has maximum temperature of $600K$. Could the experimenter heat the sample to $900K$ by using a large lens to concentrate the radiation from the large object onto the sample as shown below?

• A. Yes, if the front area of the large object is at least $1.5$ times the area of the front of the sample
• B. Yes, if the sample is placed at the focal point of the lens
• C. It is not possible
• D. Yes, if the volume of the large object is atleast $1.5$ times the volume of the sample

Answer 1

The correct option is C It is not possible

It is not possible because it will violate the second law of thermodynamics (Clausius statements). If we consider imaginary case in which temperature of sample becomes more than $600K$, then it will radiate power is more than absorbed power. Hence, it will correspond to decreasing temperature situation. So, it is not possible to heat the sample of $900K$.