Option G – Electromagnetic waves - MrSimonPorter

capricioustelephoneΠολεοδομικά Έργα

16 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

86 εμφανίσεις

Option G


Electromagnetic waves


Lesson 1


Outline the nature of electromagnetic (EM)
waves.


Describe the different regions of the
electromagnetic spectrum.


Describe what is meant by the dispersion of
EM waves.


Describe the dispersion of EM waves in terms
of the dependence of refractive index on
wavelength.

Nature of electromagnetic waves


Nature of electromagnetic waves


An
oscillating electric charge
produces varying
electric and magnetic fields.


Electromagnetic waves are
transverse waves
and all have the same speed in a vacuum.

Electromagnetic spectrum

λ

≈ 700
-

420 nm

λ

≈ 10
-
7

-

10
-
8

m

λ

≈ 10
-
9

-

10
-
11

m

λ

≈ 10
-
12

-

10
-
14

m

λ

≈ 10
-
4

-

10
-
6

m

λ

≈ 10
-
2

-

10
-
3

m

λ

≈ 10
-
1

-

10
3

m

Source of electromagnetic waves?


You have 15 minutes to take notes from pages
600 and 601 about how different EM waves
are produced.
http://phet.colorado.edu/sims/radio
-
waves/radio
-
waves_en.jar

Type

Source

Radio

Microwaves

Infra
-
red

Visible

Ultraviolet

X Ray

Gamma

Sources of EM radiation

Type

Source

Radio

Vibrating electrons e.g. AC current

Microwaves

Excited semiconductors or vibrating electrons

Infra
-
red

Electrons

transitions between
energy levels

Visible

Electrons

transitions between
energy levels

Ultraviolet

Electrons

transitions between
energy levels


X Ray

Emitted when decelerate

rapidly electrons e.g. when they
hit a metal target

Gamma

Emitted

by nuclei after a nuclear reaction


Dispersion

Let’s make rainbows!

A reminder
-

Snell’s law


speed in substance 1




sinθ
1


speed in substance 2



sinθ
2









=

A reminder
-

Snell’s law


In the case of light only, we usually define a quantity
called the
index of refraction

for a given medium as




n =

c





c
m

where
c

is the speed of

light in a vacuum and
c
m


is the speed of light in the

medium









vacuum

c

c
m

Dispersion


This occurs because the index of refraction of
the glass changes with wavelength. The index
of refraction is slightly smaller for red light
than it is for blue light, so the red light gets
bent less.

Dispersion


Just one question!


Page 605 Question 3