electromagnetic waves.pptx

7/24/2019 electromagnetic waves.pptx

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24.1 The Nature of Electromagnetic Waves

Two straight wires connected tothe terminals of an AC generator

can create an electromagnetic

wave.

Only the electric wave traveling to the

right is shown here.


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The current used to generate

the electric wave creates a

magnetic field.


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This picture shows the wave of the radiation field far from the

antenna.

The speed of an electromagnetic wave in a vacuum is:


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A radio wave can be detected with a receiving antenna wire

that is parallel to the electric field.


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With a receiving antenna in the form of a loop, the magnetic

field of a radio wave can be detected.


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24.2 The Electromagnetic Spectrum

Lie all waves, electromagnetic waves have a wavelength andfre!uency, related by:


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Example 1 The Wavelength of Visible Light

"ind the range in wavelengths for visible light in the fre!uency rangebetween #.$%&$'( and ).*%&$'(.


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Conceptual Example 2 The Diffraction of AM and FM Radio Waves

+iffraction is the ability of a wave to bend around an obstacle or the

edges of an opening. Would you e%pect A or " radio waves to

bend more readily around an obstacle such as a building-


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24.3 The Spee of !ight

The spee of lightin a vacuum


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Conceptual Example 3 Looking Back in Time

A supernova is a violent e%plosion that occurs at the death of certainstars. The figure shows a photograph of the sy before and after a

supernova. Why do astronomers say that viewing an event lie this

is lie looing bac in time-


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"axwell#s preiction of the spee of light

C


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24.4 The Energ$ Carrie %$ Electromagnetic Waves

lectromagnetic waves, lie water waves, carry energy.

24 4 Th E C i % El t ti W


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The total energ$ ensit$ carrie %$ an electromagnetic

wave

24 4 Th E C i % El t ti W


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24 & Th ' l Eff t El t ti W


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24.& The 'oppler Effect an Electromagnetic Waves

lectromagnetic waves also can e%hibit a +opper effect, but it

differs for two reasons:

a/0ound waves re!uire a medium, whereas electromagnetic

waves do not.

b/"or sound, it is the motion relative to the medium that is important.

"or electromagnetic waves, only the relative motion of the sourceand observer is important.

24 & Th ' l Eff t El t ti W


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Example ( Radar Guns and !eed Tra!s

The radar gun of a police car emits an electromagnetic wave with a

fre!uency of 1.$%&$*'(. The approach is essentially head on. The

wave from the gun reflects from the speeding car and returns to the

police car, where on2board e!uipment measures its fre!uency to be

greater than the emitted wave by 3&$$ '(. "ind the speed of

the car with respect to the highway. The police car is pared.

24 & The 'oppler Effect an Electromagnetic Waves


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fre!uency 4observed5

by speeding car

fre!uency observedby police car

24 ( )olari*ation


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24.( )olari*ation

Linearly polari(ed wave

on a rope.

6OLA789+ LCT7OA;T8C WA


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24.( )olari*ation

8n polari(ed light, the electric field

fluctuates along a single direction.

24 ( )olari*ation


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24.( )olari*ation

6olari(ed light may be produced from unpolari(ed light with

the aid of polari(ing material.

24 ( )olari*ation


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24.( )olari*ation

AL=0> LAW

intensity before

analy(erintensity after

analy(er

24 ( )olari*ation


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24.( )olari*ation

Example + "sing #olari$ers and Anal%$ers

What value of ? should be used so the average intensity of the polari(ed

light reaching the photocell is one2tenth the average intensity of the

unpolari(ed light-

24 ( )olari*ation


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24.( )olari*ation

24 ( )olari*ation


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24.( )olari*ation

When 6olaroid sunglasses are

crossed, the intensity of the

transmitted light is reduced to

(ero.

24 ( )olari*ation


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24.( )olari*ation

,"- movie pro/ector

24.( )olari*ation


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24.( )olari*ation

Conceptual Example 0 &o' (an a (rossed #olari$er and

Anal%$er Transmit Light)

0uppose that a third piece of polari(ing material is insertedbetween the polari(er and analy(er. +oes light now reach the

photocell-

24.( )olari*ation


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24.( )olari*ation

T' OCC=7A;C O" 6OLA789+ L8'T 8; ;AT=7

electromagnetic waves.pptx

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