# Worksheet: Thermal Convection

In this worksheet, we will practice describing the origins and effects of thermal convection currents in liquids and gases.

Q1:

A container holds a liquid that is steadily heated from the top of the container. Which of the following diagrams most correctly shows the motion and temperature change of the liquid in the container due to convection?

• A • B • C • D Q2:

A container holds a liquid that is steadily heated from the base of the container. Which of the following diagrams most correctly shows the motion and temperature change of the liquid in the container due to convection?

• A • B • C • D Q3:

A fluid is in a container that is steadily heated from the base. The region of the fluid that is most directly heated thermally expands, reducing its density, as shown in the diagram. Which of the following diagrams most correctly shows both how the lower- and higher-density fluid regions would be distributed through the fluid and how these regions would heat each other? • A • B • C • D Q4:

The diagram shows two freely moving particles in a container. Both particles have the same mass. The positions of the particles shown are the highest points above the base of the container that the particles reach. Neither particle has any horizontal motion. What is the ratio of the kinetic energy of the higher particle to that of the lower particle when both particles are at the base of the container?

• A
• B
• C
• D

Q5:

The diagram shows two land surfaces that have the temperatures and , where > . The air above the land surfaces has net horizontal motion with different directions at different heights. The dashed line is at a height where the net horizontal motion of the air is zero. What is the direction of airflow between the points A and B?

• AFrom A to B
• BFrom B to A

What is the direction of airflow between the points C and D?

• AFrom D to C
• BFrom C to D

Q6:

The diagram shows the change of temperature with density of water in a container that is steadily heated from the container’s base. The points I, II, and III represent the density and temperature of regions of water in the container at different heights above the container’s base. The graph shows the full range of temperatures and densities of the water regions. How would the height of the region of water above the container base change between point I and point II?

• AIt remains constant.
• BIt increases.
• CIt decreases.

If the regions of water at points II and III were of equal volume, which region would have a greater mass?

• AThe point III region
• BThe point II region
• CThe masses are the same.

Q7:

The diagram shows particles in a liquid. The liquid consists of two regions with temperatures and , where . The higher-temperature region moves toward the lower-temperature region and there are collisions between particles at the boundary of the regions. In which region do the particles have a higher average kinetic energy?

• AThe upper region
• BThe average kinetic energy is the same in both regions.
• CThe lower region

Which region will lose internal energy due to the collisions between the particles?

• AThere will be no net change in internal energy for either region.
• BThe lower region
• CThe upper region

Q8:

A fluid in a container has a higher density region, as shown in the diagram. The higher-density region is above a steadily heated region. Which of the following statements correctly describe why the higher density region moves toward the bottom of the container?

1. The downward momentum of higher density fluid is greater than the upward momentum of an equal volume of fluid below it with which it is in contact.
2. The weight of higher density fluid is greater than the upthrust force from an equal volume of fluid below it.
3. Because the higher density fluid is at a greater height than the fluid below it, it has a greater downward gravitational force acting on it.
4. At the points that the fluids are in contact, the higher density region applies a greater pressure on the fluid below it than the fluid below the higher density region applies on it.
• Ab
• Ba and b
• Cd
• Db and c
• Eb and d

How does the temperature of the heated region change due to it being heated?

• AIt remains constant.
• BIt increases.
• CIt decreases.

How does the density of the heated region change due to it being heated?

• AIt increases.
• BIt remains constant.
• CIt decreases.

Q9:

The diagram shows two surfaces that have the temperatures and , where > . On the surface with temperature , a fan blows air toward the other surface. The air above the surfaces has zero net horizontal motion due to convection of air at the height shown by the dashed line when the fan is not rotating. When the fan rotates, how does the vertical position of the dashed line change? • AThe line moves upward.
• BThe line does not change position.
• CThe line moves downward.

Q10:

A fluid in a container is heated from the container’s base so that the fluid near the base is steadily heated. The heated fluid region contains lower-density fluid than that in the rest of the container. Which of the following statements most correctly explains how a lower-density region of fluid can exist underneath a higher-density region of fluid? • AThe fluid that is heated continually undergoes thermal expansion.
• BBecause the lower-density fluid is closer to the ground than the fluid above it, it has a greater downward gravitational force acting on it.
• CThe upward momentum of the lower-density fluid is greater than the downward momentum of an equal volume of the fluid above it with which it is in contact.
• DAt the points that the fluids are in contact, the lower-density region applies a greater pressure on the fluid above it than the fluid above the lower-density region applies on it.