AP Physics 2: Algebra-Based Practice Quiz: Blackbody Radiation

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 11 questions to check your progress.

Question 1 of 11

According to the provided text, what is an idealized blackbody?

A)An object that reflects all radiation that falls on it.B)An object that absorbs all radiation that falls on it.C)An object that only emits radiation at a single wavelength.D)An object whose emitted radiation depends on its composition.

All Questions (11)

According to the provided text, what is an idealized blackbody?

A) An object that reflects all radiation that falls on it.

B) An object that absorbs all radiation that falls on it.

C) An object that only emits radiation at a single wavelength.

D) An object whose emitted radiation depends on its composition.

Correct Answer: B

The content explicitly states, 'A blackbody is an idealized model of matter that absorbs all radiation that falls on the body.'

The continuous spectrum of electromagnetic radiation emitted by a blackbody depends only on which of the following properties?

A) The body's temperature

B) The body's surface area

C) The body's chemical composition

D) The radiation that falls on the body

Correct Answer: A

The content specifies that 'A blackbody will emit a continuous spectrum that only depends on the body’s temperature.'

According to Wien’s law, what happens to the peak wavelength of the radiation emitted by a blackbody as its temperature increases?

A) It increases.

B) It decreases.

C) It remains the same.

D) It becomes zero.

Correct Answer: B

The content states, 'The peak wavelength emitted by a blackbody (λ_max) decreases with increasing temperature, as described by Wien’s law.'

The Stefan–Boltzmann law describes the rate at which a blackbody emits energy. This rate is proportional to the body's surface area and what other quantity?

A) The temperature of the body

B) The square of the temperature of the body

C) The cube of the temperature of the body

D) The fourth power of the temperature of the body

Correct Answer: D

The content explains that the rate of energy emission is 'proportional to the surface area of the body and to the temperature of the body raised to the fourth power, as described by the Stefan–Boltzmann law.'

A blackbody has a temperature T and emits radiation with a peak wavelength of λ_max. If the temperature of the blackbody is tripled to 3T, what will be the new peak wavelength?

A) 9λ_max

B) 3λ_max

C) λ_max / 3

D) λ_max / 9

Correct Answer: C

According to Wien’s law, λ_max * T = b, where b is a constant. This means λ_max is inversely proportional to T. If T is tripled, λ_max must decrease by a factor of 3, becoming λ_max / 3.

A blackbody at temperature T radiates energy at a rate (power) of P. If the temperature of the blackbody is doubled to 2T, while its surface area remains constant, what is the new rate of energy radiation?

A) 2P

B) 4P

C) 8P

D) 16P

Correct Answer: D

The Stefan–Boltzmann law states that the power is proportional to the temperature raised to the fourth power (P ∝ T⁴). If the temperature is doubled (2T), the new power will be proportional to (2T)⁴ = 16T⁴. Therefore, the new power is 16 times the original power P.

Which of the following statements best describes the electromagnetic radiation emitted by an object due to its temperature?

A) It is emitted only by objects at very high temperatures.

B) It consists of a single, discrete wavelength.

C) It is a fundamental property of matter that depends on temperature.

D) It is always in the visible part of the spectrum.

Correct Answer: C

The first point of the content describes this as 'the electromagnetic radiation emitted by an object due to its temperature.' The third point clarifies it's a continuous spectrum dependent only on temperature, making it a fundamental property of any object with a temperature.

An astronomer observes two stars, Star X and Star Y, treating them as ideal blackbodies. Star X has a peak emission in the blue part of the spectrum, while Star Y has a peak emission in the red part of the spectrum. Given that blue light has a shorter wavelength than red light, which conclusion is supported by Wien's law?

A) Star X is hotter than Star Y.

B) Star Y is hotter than Star X.

C) Both stars have the same temperature.

D) The temperature cannot be determined from the peak wavelength.

Correct Answer: A

Wien’s law states that the peak wavelength (λ_max) is inversely proportional to temperature (T). Since Star X has a shorter peak wavelength (blue) than Star Y (red), it must have a higher temperature.

Consider two spherical blackbodies, Sphere A and Sphere B. The temperature of Sphere A is twice the temperature of Sphere B. The surface area of Sphere A is half the surface area of Sphere B. What is the ratio of the power radiated by Sphere A to the power radiated by Sphere B (P_A / P_B)?

A) 2

B) 4

C) 8

D) 16

Correct Answer: C

According to the Stefan–Boltzmann law, power (P) is proportional to surface area (A) and the fourth power of temperature (T⁴), so P ∝ AT⁴. We have T_A = 2T_B and A_A = 0.5A_B. The ratio is P_A / P_B = (A_A * T_A⁴) / (A_B * T_B⁴) = (0.5A_B * (2T_B)⁴) / (A_B * T_B⁴) = (0.5A_B * 16T_B⁴) / (A_B * T_B⁴) = 0.5 * 16 = 8.

Based on the provided description, what is the primary characteristic of an idealized blackbody's interaction with incident radiation?

A) Perfect reflection

B) Perfect absorption

C) Perfect transmission

D) Partial absorption and partial reflection

Correct Answer: B

The content defines a blackbody as 'an idealized model of matter that absorbs all radiation that falls on the body.' This means it is a perfect absorber.

An object behaving as a blackbody is heated, causing its temperature to increase significantly. According to the principles of blackbody radiation, which of the following correctly describes the changes in its emitted radiation?

A) The peak wavelength increases, and the total power emitted decreases.

B) The peak wavelength decreases, and the total power emitted increases.

C) The peak wavelength remains the same, but the total power emitted increases.

D) The peak wavelength decreases, but the total power emitted remains the same.

Correct Answer: B

This question combines two laws. According to Wien’s law, as temperature increases, the peak wavelength decreases. According to the Stefan–Boltzmann law, as temperature increases, the power emitted (proportional to T⁴) increases.