# Expressing entropy of black body radiation

• desertgirl
In summary, black body radiation refers to the electromagnetic radiation emitted by an object that absorbs all radiation and does not reflect or transmit any. It is important in thermodynamics and has practical applications in fields such as astrophysics. In the context of black body radiation, entropy is a measure of disorder or randomness and is expressed using the Stefan-Boltzmann law. The units of entropy are joules per kelvin (J/K) or joules per mole-kelvin (J/mol-K).
desertgirl

## Homework Statement

By applying the first law to a quasi static process, show that the entropy can be expressed as
S = (16σ/3c) VT3

U = 4(σ/c) VT4
PV = 1/3 U[/B]

## The Attempt at a Solution

I know I should be using
dS = dQ/T but it's unclear to me how to use this unless I took the integral for arbitrary volumes, I couldn't find any examples in my text or online to try and get it myself [/B]

Hello, and welcome to PF!
Show how you are attempting to apply the first law.

## 1. What is black body radiation?

Black body radiation refers to the electromagnetic radiation emitted by a theoretical object that absorbs all radiation that falls on it, and does not reflect or transmit any. It is also known as Planck's radiation or thermal radiation.

## 2. Why is black body radiation important?

Black body radiation is important because it is a fundamental concept in thermodynamics and plays a crucial role in our understanding of the behavior of matter at high temperatures. It also has practical applications in fields such as astrophysics, where it helps us understand the properties of stars and other celestial bodies.

## 3. What is entropy in the context of black body radiation?

In the context of black body radiation, entropy refers to the measure of disorder or randomness of the radiation emitted by the black body. It is a fundamental concept in thermodynamics and is related to the amount of energy that is unavailable to do work.

## 4. How is entropy of black body radiation expressed?

The entropy of black body radiation is expressed using the Stefan-Boltzmann law, which states that the total amount of energy emitted by a black body is proportional to the fourth power of its absolute temperature. This law is also used to calculate the temperature of a black body based on the amount of radiation it emits.

## 5. What are the units of entropy in black body radiation?

The units of entropy in black body radiation are joules per kelvin (J/K). This is because entropy is a measure of energy per unit temperature, and both energy and temperature have their own respective units of joules and kelvin. In some cases, the unit of entropy may also be expressed as joules per mole-kelvin (J/mol-K) for convenience.

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