# GRE Subject Test: Physics : Astrophysics

## Example Questions

### Example Question #1 : Astrophysics

If the temperature of a blackbody doubles, what occurs to the wavelength of maximum emission?

It doubles.

It is quartered.

It is halved.

No change.

It is halved.

Explanation:

This is an application of Wein's Law that states the following:

, where  is the wavelength of maximum emission of the object (measured in ), and  is the temperature in . Since the wavelength and the temperature are inversely proportional, if we double the temperature, we must cut the wavelength by the same proportion. Therefore, the temperature must be halved.

### Example Question #2 : Astrophysics

By what factor will the energy emitted each second off the surface of a blackbody change if the the temperature of the object is tripled?

Explanation:

Stefan-Boltzmann's equation for a blackbody states:

, where  is the energy emitted each second,  is the Stefan-Boltzmann constant, and  is the temperature of the blackbody. Therefore, if we triple the temperature, the energy will increase by a factor of

### Example Question #3 : Astrophysics

Using the kinetic theory of gas, what is the fundamental property of a planet that dictates if it is able to retain an atmosphere?

Energy

Magnetic field strength

Number of moons

Temperature

Mass