Methods of Energy Transfer

The transfer of heat energy from a hot object can occur in three ways:

• Conduction is the transfer of energy as heat through a material.

• Convection is the movement of matter due to differences in density that are caused by temperature variations.

• Radiation is the energy that is transferred as electromagnetic waves, such as visible light and infrared waves.

Methods of Energy Transfer, continued

Conduction• Conduction involves objects in direct contact.• Conduction takes place when two objects that are in

contact are at unequal temperatures.

Methods of Energy Transfer, continued

Convection• Convection results from the

movement of warm fluids. • During convection, energy is

carried away by a heated fluid that expands and rises above cooler, denser fluids.

• A convection current is the vertical movement of air currents due to temperature variations.

Methods of Energy Transfer, continued

Radiation• Radiation is energy transferred as heat in the form of

electromagnetic waves.

• Unlike conduction and convection, radiation does not involve the movement of matter.

• Radiation is therefore the only method of energy transfer that can take place in a vacuum.

• Much of the energy we receive from the sun is transferred by radiation.

Comparing Convection, Conduction, and Radiation

Click below to watch the Visual Concept.

Visual Concept

Concept Mapping

Conductors and Insulators• Any material through which energy can be easily

transferred as heat is called a conductor.

• Poor conductors are called insulators.

• Gases are extremely poor conductors.

• Liquids are also poor conductors.

• Some solids, such as rubber and wood, are good insulators.

• Most metals are good conductors.

Specific Heat• Specific heat describes how much energy is required

to raise an object’s temperature.• Specific heat is defined as the quantity of heat

required to raise a unit mass of homogenous material 1 K or 1°C in a specified way given constant pressure and volume.

Specific Heat Equationenergy = (specific heat) (mass) (temperature change)

energy = cmt

Understanding Concepts, continued3. What transfer method carries energy from

the sun to Earth?

A. conductionB. convection C. insulationD. radiation

Standardized Test PrepChapter 13

Understanding Concepts, continued3. What transfer method carries energy from

the sun to Earth?

A. conductionB. convection C. insulationD. radiation

Standardized Test PrepChapter 13

Understanding Concepts, continued4. Why does the temperature of hot chocolate

decrease faster if you place a metal spoon in the liquid?

Answer: Metal is a good conductor of heat, so energy is transferred rapidly to the metal and from the metal to the air.

Standardized Test PrepChapter 13

Interpreting Graphics

Standardized Test Prep

7. What form of heat transfer is represented by this illustration?

F. conduction G. convection H. insulationI. radiation

Chapter 13

Bellringer

The three pictures all show examples of energy transfer. Answer the questions about what happens in each picture, and identify how the heat got from one object to another in each case.

Section 2 Energy Transfer

1. Why is it a bad idea to drink hot cocoa out of a tin cup? Explain the energy transfers on the atomic level.

Chapter 13

Bellringer, continuedSection 2 Energy Transfer

2. What happens to your hand when you place it above a lighted candle? (Assume you are not touching the flame. Explain the energy transfers on the atomic level. Hint: Remember that warm air rises.)

3. When you sit near a fire, you can feel its warmth on your skin, even if you are in cool air. Does this sensation depend upon the fact that warm air rises?

Chapter 13