DP Physics Questionbank

X and Y are two spherical black-body radiators that emit the same total power. The absolute temperature of X is half that of Y. 

What is $\frac{\text{radius of X}}{\text{radius of Y}}$?

A. 4

B. 8 

C. 16 

D. 32

The average surface temperature of Mars is approximately 200 K and the average surface temperature of Earth is approximately 300 K. Mars has a radius half that of Earth. Assume that both Mars and Earth act as black bodies.

What is $\frac{\text{power radiated by Mars}}{\text{power radiated by Earth}}$?

A.  20
B.  5
C.  0.2
D.  0.05

A room is at a constant temperature of 300 K. A hotplate in the room is at a temperature of 400 K and loses energy by radiation at a rate of P. What is the rate of loss of energy from the hotplate when its temperature is 500 K?

A.  $\frac{4^4}{5^4}$P

B.  $\frac{5^4+3^4}{4^4+3^4}$P

C.  $\frac{5^4}{4^4}$P

D.  $\frac{5^4-3^4}{4^4-3^4}$P

The average albedo of glacier ice is 0.25.

What is $\frac{\text{power absorbed by glacier ice}}{\text{power reflected by glacier ice}}$?

A.  0.25

B.  0.33

C.  2.5

D.  3.0

The average temperature of the surface of a planet is five times greater than the average temperature of the surface of its moon. The emissivities of the planet and the moon are the same. The average intensity radiated by the planet is $I$. What is the average intensity radiated by its moon?

A.  $\frac{I}{25}$

B.  $\frac{I}{125}$

C.  $\frac{I}{625}$

D.  $\frac{I}{3125}$

A black body emits radiation with its greatest intensity at a wavelength of I_max. The surface temperature of the black body doubles without any other change occurring. What is the wavelength at which the greatest intensity of radiation is emitted?

A. I_max

B. $\frac{\text{I}{}_{\text{max}}}{\text{2}}$

C. $\frac{\text{I}{}_{\text{max}}}{\text{4}}$

D. $\frac{\text{I}{}_{\text{max}}}{\text{16}}$

Determine the mean temperature of the Earth.

The albedo of the planet is ${\alpha }_{\text{p}}$. The equilibrium surface temperature of the planet is T. Derive the expression

$T=\sqrt[4]{\frac{P(1-{\alpha }_{\text{p}})}{16\pi d^{2}e\sigma }}$

where e is the emissivity of the planet.

Explain why the power incident on the planet is

                                                                $\frac{P}{4\pi d^2}\times \frac{A}{4}.$

On average, the Moon is the same distance from the Sun as the Earth. The Moon can be assumed to have an emissivity e = 1 and an albedo ${\alpha }_{\text{M}}$ = 0.13. The solar constant is 1.36 × 103 W m⁻². Calculate the surface temperature of the Moon.

A black body at temperature T emits radiation with peak wavelength ${\lambda }_{\text{ρ}}$ and power P. What is the temperature of the black body and the power emitted for a peak wavelength of $\frac{{\lambda }_{\text{ρ}}}{2}$?

A black-body radiator emits a peak wavelength of ${\lambda }_{\text{max}}$ and a maximum power of $P_0$. The peak wavelength emitted by a second black-body radiator with the same surface area is $2 {\lambda }_{\text{max}}$. What is the total power of the second black-body radiator?

A.  $\frac{1}{16}{P}_0$

B.  $\frac{1}{2}{P}_0$

C.  $2P_0$

D.  $16P_0$

Calculate the peak wavelength in the intensity of the radiation emitted by the ice sample.

State what is meant by thermal radiation.

Discuss how the frequency of the radiation emitted by a black body can be used to estimate the temperature of the body.

Three gases in the atmosphere are

          I.     carbon dioxide (CO₂)

          II.     dinitrogen monoxide (N₂O)

          III.     oxygen (O₂).

Which of these are considered to be greenhouse gases?

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

Mars and Earth act as black bodies. The $\frac{\text{power radiated by Mars}}{\text{power radiated by the Earth}}=p$ and $\frac{\text{absolute mean temperature of the surface of Mars}}{\text{absolute mean temperature of the surface of the Earth}}=t$.

What is the value of $\frac{\text{radius of Mars}}{\text{radius of the Earth}}$?

A.     $\frac{p}{t^4}$

B.     $\frac{\sqrt{p}}{t^2}$

C.     $\frac{t^4}{p}$

D.     $\frac{t^2}{\sqrt{p}}$

Titan has an atmosphere of nitrogen. The albedo of the atmosphere is 0.22. The surface of Titan may be assumed to be a black body. Explain why the average intensity of solar radiation absorbed by the whole surface of Titan is 3.1 W m⁻²

Titan has an atmosphere of nitrogen. The albedo of the atmosphere is 0.22. The surface of Titan may be assumed to be a black body. Explain why the average intensity of solar radiation absorbed by the whole surface of Titan is 3.1 W m⁻².

Discuss how the frequency of the radiation emitted by a black body can be used to estimate the temperature of the body.

State what is meant by thermal radiation.

Calculate the peak wavelength in the intensity of the radiation emitted by the ice sample.

Show that the intensity of solar radiation at the orbit of Mars is about 600 W m^–2.

Determine, in K, the mean surface temperature of Mars. Assume that Mars acts as a black body.

Show that the intensity of solar radiation at the orbit of Mars is about 600 W m^–2.

Determine, in K, the mean surface temperature of Mars. Assume that Mars acts as a black body.

The diagram shows, for a region on the Earth’s surface, the incident, radiated and reflected intensities of the solar radiation.

What is the albedo of the region?

A.  $\frac{1}{4}$

B.  $\frac{1}{3}$

C.  $\frac{3}{4}$

D.  $1$

The missing section of insulation is 0.56 m long and the external radius of the pipe is 0.067 m. The emissivity of the pipe surface is 0.40. Determine the energy lost every second from the pipe surface. Ignore any absorption of radiation by the pipe surface.

Describe one other method by which significant amounts of energy can be transferred from the pipe to the surroundings.

The albedo of the Earth’s atmosphere is 0.28. Outline why the maximum temperature of a black body on the Earth when the Sun is overhead is less than that at point A on the Moon.

A black body is on the Moon’s surface at point A. Show that the maximum temperature that this body can reach is 400 K. Assume that the Earth and the Moon are the same distance from the Sun.