20. Heat and Temperature

Which of the following best describes convection in the context of heat transfer?

Why did the transfer of energy between the two samples stop?

Which of the following processes primarily transfers heat from one object to another?

(II) Heat conduction to skin. Suppose 150 W of heat flows by conduction from the blood capillaries beneath the skin to the body’s surface area of 1.5 m². If the temperature difference is 0.50 C°, estimate the average distance of capillaries below the skin surface.

Which of the following is NOT a primary mechanism by which $\mathrm{heat}$ transfer occurs?

A steel rod is initially very cold. If it is placed close to a fire, which method of heat transfer will primarily cause the rod to become warmer?

Which type of heat transfer is primarily responsible for cooking a pancake when it is placed on a hot stove pan?

An electric kitchen range has a total wall area of $1.40$ m² and is insulated with a layer of fiberglass $4.00$ cm thick. The inside surface of the fiberglass has a temperature of $175$°C, and its outside surface is at $35.0$°C. The fiberglass has a thermal conductivity of $0.040W/m\cdot K$. What is the heat current through the insulation, assuming it may be treated as a flat slab with an area of $1.40$ m² ?

The emissivity of tungsten is $0.350$. A tungsten sphere with radius $1.50$ cm is suspended within a large evacuated enclosure whose walls are at $290.0$ K. What power input is required to maintain the sphere at $3000.0$ K if heat conduction along the supports is ignored?

The temperature within the Earth’s crust increases about 1.0 C° for each 30 m of depth. The thermal conductivity of the crust is 0.80 J/s C°. Compare this heat to the 1000 W/m² that reaches the Earth’s surface in 1.0 h from the Sun.

A cubic Styrofoam cooler containing ice on a hot day is shown in the following figure. The thickness of each wall of the cooler is 15 mm, with a side length of 1 m. If it is 40°C outside, how long will 2 kg of ice last in the cooler? Assume that during the melting process, the temperature inside the cooler remains at 0°C and that no heat enters from the bottom of the cooler. Note that the latent heat of fusion for water is 334 kJ/kg and the thermal conductivity of Styrofoam is 0.033 W/mK.

Which of the following best describes how $\mathrm{thermal energy}$ is transferred between two objects at different $\mathrm{temperatures}$?

Which of the following is NOT a primary mechanism by which heat travels from one place to another?

(I) To what temperature will 6800 J of heat raise 3.0 kg of water that is initially at 10.0°C?