Problem 14 - Campbell Biology Concepts & Connections

Question

You are in a room of empty chairs. As the chairs fill with people, you become hotter and hotter. A ceiling fan is turned on, and you feel cooler. You gained heat by ______ and lost heat to the environment by _____. a. conduction... convection b. radiation... convection c. radiation... conduction d. convection... radiation

Step-by-Step Solution

Answer

b. radiation... convection

Step 1 - Understand the Mechanism of Heat Gain

Identify how heat is transferred to you in the room. The more people in the room, the more heat is produced and shared among the individuals, primarily through the emission of infrared radiation.

Step 2 - Determine the Heat Gain Process

Since heat is gained through the emission of infrared waves from other people, the heat gain process is radiation.

Step 3 - Understand the Mechanism of Heat Loss

Identify how the ceiling fan cools you down. The fan circulates air, which removes heat from your body by moving the warm air away and replacing it with cooler air. This process is convection.

Step 4 - Determine the Heat Loss Process

Since the fan cools you through increased air movement and the removal of warm air around your body, the heat loss process is convection.

Step 5 - Select the Correct Answer

Based on the analysis, you gain heat by radiation from the people and lose heat by convection due to the fan. The correct answer is b. radiation... convection.

Key Concepts

Radiation

When you sit in a room that starts filling up with people, you might feel warmer. This isn't just because there are more bodies close to you. It's mostly because everyone in that room is radiating heat.
Radiation is a process where heat is transferred through infrared waves. These waves are a type of electromagnetic radiation.

• Radiation doesn't need a medium to travel through. It can transfer heat through the vacuum of space.
• It can be felt from a distance. This is why you can feel the warmth from a fireplace even if you're sitting across the room.
• In the context of the exercise, people are the heat sources. They emit infrared radiation that you absorb, making you feel hotter.

Radiation is one of the main ways heat moves around us, especially between objects that aren't touching.

Convection

When the ceiling fan is turned on, you start feeling cooler because of convection. Convection involves the movement of heat through fluids, which can be liquids or gases.
In this case, the fluid is air.

• When air near your skin is warmed by your body, it becomes less dense and rises.
• The ceiling fan helps by moving this warm air away from you and replacing it with cooler air.
• This continuous movement of air makes it feel cooler as it enhances the rate at which the heat is carried away from your skin.

Without the fan, the warm air would just linger around you, making it harder to lose heat. That's why fans are very effective in enhancing convection and cooling you down.

Conduction

Conduction is another important heat transfer mechanism, though it is not the primary focus in this exercise. Conduction happens when heat transfers through direct contact between materials.

• Think of a metal spoon in a hot cup of soup. The heat moves from the hot soup to the cooler spoon handle.
• Heat moves from the warmer object to the cooler one until they both reach the same temperature.
• Conduction requires a solid medium or direct contact for the heat transfer to happen effectively.

In the context of a room with people, conduction could occur if you were touching another person or an object that was warmer or cooler than you. However, in the given exercise, you primarily gain heat from others through radiation and lose it through convection.