Thermal Energy- Radiation

​Thermal Radiation

​By: Feri Vahabi

​

Someone is warming their hands over a bonfire. They don’t have to touch the fire to feel its warmth. How is warmth from the fire transferred to their hands?

​Introducing Thermal Radiation

The bonfire from the opening image has a lot of thermal energy. Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Thermal energy from the bonfire is transferred to the hands by thermal radiation. 

Multiple Choice

1. What is thermal energy?

• The energy stored in batteries

• The energy produced by nuclear reactions

• The total kinetic energy of moving particles of matte

• The energy released during combustion

Multiple Choice

How is thermal energy transferred from a bonfire to the hands of someone sitting nearby?

• Conduction

• Convection

• Thermal radiation

• Fusion

Multiple Choice

1. What is thermal radiation?

• The transfer of energy through direct contact between particles

• The transfer of energy through the movement of fluids

• The transfer of energy by waves that can travel through air or empty space

• The transfer of energy through electromagnetic fields

​Thermal radiation is the transfer of thermal energy by waves that can travel through air or even through empty space, as shown in the Figure 2. When the waves of thermal energy reach objects, they transfer the energy to the objects, causing them to warm up. This is how the fire warms the hands of someone sitting near the bonfire. This is also how the sun’s energy reaches Earth and heats its surface. Without the energy radiated from the sun, Earth would be too cold to support life as we know it.

Multiple Choice

1. How does thermal radiation from the sun reach Earth's surface?

• Through conduction

• Through convection

• Through thermal insulation

• Through waves that can travel through air or empty space

​Thermal radiation is one of three ways that thermal energy can be transferred. The other two ways are conduction and convection, both of which need matter to transfer energy. Radiation is the only way of transferring thermal energy that doesn’t require matter. 

Multiple Choice

1. Which of the following requires matter to transfer thermal energy?

• Conduction

• Convection

• Radiation

• Both a) and b)

Multiple Choice

1. What is the only method of transferring thermal energy that doesn't require matter?

• Conduction

• Convection

• Radiation

• All of the above

Sources of Thermal Radiation

You might be surprised to learn that everything radiates thermal energy, not just really hot things such as the sun or a fire. For example, when it’s cold outside, a heated home radiates some of its thermal energy into the outdoor environment. A home that is poorly insulated radiates more energy than a home that is well insulated. Special cameras can be used to detect radiated heat.

In the Figure 3, you can see an image created by one of these cameras. The areas that are yellow are the areas where the greatest amount of thermal energy is radiating from the home. Even people radiate thermal energy. In fact, when a room is full of people, it may feel noticeably warmer because of all the thermal energy the people radiate!

Multiple Choice

1. Which statement about thermal energy radiation is true?

• Only hot objects such as the sun or fire radiate thermal energy.

• Everything, including cold objects, radiates thermal energy.

• Thermal energy radiation only occurs indoors.

• Thermal energy radiation is not affected by insulation.

Multiple Choice

1. How does insulation affect the radiation of thermal energy from a home?

• Insulation increases the radiation of thermal energy.

• Insulation decreases the radiation of thermal energy.

• Insulation has no effect on the radiation of thermal energy.

• Insulation changes the color of thermal energy radiation.

Multiple Choice

What color is the best at reflecting the heat radiation?

• Matte black

• Shiny Silver

• Black

• Red

Multiple Choice

What is the best color at emitting heat radiation?

• Matte black

• black

• White

• Matte white

Multiple Choice

1. How can radiated heat from a home be detected?

• Using a thermometer

• Using a barometer

• Using a special camera

• Using a magnifying glass