Two identical objects are placed in a room with a temperature of 20°C. Object A has a temperature of 50°C, while object B has a temperature of 90°C. What is the ratio of the net power emitted by object B to that emitted by object A?
A) 1.7
B) 2.8
C) 81
D) 17
E) 21

Question

Quizplus · Accepted Answer

The net power emitted by an object is proportional to the fourth power of its absolute temperature. 
Let T be the absolute temperature of each object. 
Then, we have:
Power emitted by A = kT^4, where k is a constant of proportionality.
Power emitted by B = k(2T)^4 = 16kT^4. 
Therefore, the ratio of the power emitted by B to that emitted by A is:
(16kT^4) / (kT^4) = 16. 
Since object B has a temperature that is twice that of object A, its net power emitted is 16 times greater than that of object A. Thus, the answer is B.

Two Identical Objects Are Placed in a Room with a Temperature