Question 1

Which of the following best describes the process of heat transfer by conduction?

Accepted Answer

Heat is transferred by direct collisions between particles in matter.

Question 2

A metal rod is heated at one end. Which equation correctly gives the rate of heat transfer through the rod by conduction?

Accepted Answer

$$ \frac{dQ}{dt} = kA \frac{\Delta T}{L} $$

Question 3

Which material would be the best insulator for minimizing heat loss through conduction, based on its thermal conductivity?

Accepted Answer

Styrofoam ($$k = 0.035 W/mK)$$

Question 4

A house uses glass windows ($$k = 0.8 W/mK) $$and Styrofoam insulation ($$k = 0.035 W/mK). If $$both have the same thickness and area, which will allow more heat to escape and why?

Accepted Answer

Glass, because it has a higher thermal conductivity.

Question 5

Which of the following is an example of heat transfer by convection?

Accepted Answer

Warm air rising above a heater in a room.

Question 6

Which equation describes the net rate of heat transfer by radiation from an object at temperature $$T in an $$environment at temperature $$T_0$$?

Accepted Answer

$$ \frac{dQ}{dt} = e\sigma A (T^4$ - T_0$^4) $$

Question 7

A freezer is kept at $$-20^\circC in a $$room at $$25^\circC. If $$the total surface area is $$7.24 m$^2$$, the insulation thickness is $$0.050 m$$, and $$k = 0.035 W/mK$$, what is the rate of heat entering the freezer?

Accepted Answer

$$230 W$$

Question 8

Which of the following statements about black bodies is correct?

Accepted Answer

A black body absorbs all incident radiation and emits the maximum possible radiation.

Question 9

The greenhouse effect is primarily caused by which process?

Accepted Answer

The absorption and re-emission of infrared radiation by atmospheric gases.

Question 10

If the temperature difference across a wall doubles, what happens to the rate of heat transfer by conduction, assuming all other factors remain constant?

Accepted Answer

It doubles.

Question 11

Which of the following is NOT a mechanism of heat transfer discussed in the materials?

Accepted Answer

Diffusion

Question 12

A black surface and a shiny metallic surface are both exposed to sunlight. Which will heat up faster and why?

Accepted Answer

The black surface, because it has a higher emissivity.

Question 13

Which of the following best explains why you feel warm standing near a campfire, even if the air is cold?

Accepted Answer

Heat is transferred to you by radiation.

Question 14

Given the Stefan-Boltzmann law, $$ \frac{dQ}{dt} = e\sigma AT^4$ $$, what is the physical meaning of the parameter $$e$$?

Accepted Answer

It is the emissivity, a measure of how effectively a surface emits radiation.

Question 15

A Styrofoam cup is used to keep a drink cold. Which property of Styrofoam makes it effective for this purpose?

Accepted Answer

Low thermal conductivity

Question 16

Which of the following scenarios is an example of heat transfer by evaporation?

Accepted Answer

Sweat evaporating from your skin, cooling you down.

Question 17

If the thickness $$L of an $$insulating wall is doubled, what happens to the rate of heat transfer by conduction, assuming all other factors remain constant?

Accepted Answer

It is halved.

Question 18

Which of the following best describes why the sun can heat the Earth through the vacuum of space?

Accepted Answer

Heat is transferred by radiation, which does not require a medium.

Question 19

A satellite measures the intensity of solar radiation at Earth's distance as $$1370 W/m$^2. If $$the sun's radius is $$6.96 	imes 10^8$ m, what is the formula to estimate the sun's surface temperature T$?

Accepted Answer

$$ T = \left[ \frac{dQ/dt}{e\sigma (4\pi R_S^2$)} \right]^{1/4} $$

Heat Transfer Mechanisms in Physics

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