Lesson 3.3 - Heat Transfer: Radiation

You have warmed your hands in front of a fire or a fireplace. You do not touch the fire or fireplace and the air around your hands is not hot, yet your hands warm up. How is the heat transferred to your hands?

Read Radiation on page 89 of your textbook.

Question 1. How is heat transferred by radiation?

Question 2. Is physical contact between objects or substances required for heat to be transferred by radiation?

Question 3. Is a substance (solid, liquid, or gas) required for heat to be transferred by radiation?

Check your answers with those that follow.

 

Have you ever been to a Calgary Flames hockey game? The Saddledome has some flame throwers that are fired whenever Calgary scores a goal. You can feel immediately the heat from the flame anywhere in the building. The heat that you feel is a result of radiation. How would you know the heat is transferred by radiation and not conduction or convection? You are not touched by the flame or any of the hot parts, so it cannot be by conduction. You can feel the heat immediately, convection would take a long time for the heated air to move from the flame to your body, so it cannot be by convection.

Question 4. How can you tell if heat is transferred by radiation?

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. How is heat transferred by radiation?

Heat is transferred by radiation in the following manner. All particles give off infrared radiation. The hotter the particles, the more infrared radiation is given off. Infrared radiation is very similar to light radiation; it is just a much lower wavelength. When this radiation is absorbed by an object it is converted to kinetic energy. Thus, the hot object radiates infrared radiation and cools down, the cold object absorbs the infrared radiation and heats up.

Question 2. Is physical contact between objects or substances required for heat to be transferred by radiation?

No, physical contact is not required for heat to be transferred by radiation.

Question 3. Is a substance, (solid, liquid, or gas), required for heat to be transferred by radiation?

No, heat can be transferred by radiation through empty space because electromagnetic radiation does not require a medium for transmission.

 

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Answers to Questions:

Question 4. How can you tell if heat is transferred by radiation?

You can tell that heat is transferred by radiation if the transfer did not occur by conduction or convection. You can also tell if you are far away from the heat source and you feel the heat instantly.


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