Module 4 - Waves (Electromagnetic waves)

Question 1

T/F EM waves are transverse

Answer 1

True

Question 2

What is the source of EM waves

Answer 2

• Electric and Magnetic fields oscillating perpendicular to each other

Question 3

What speed do EM waves travel at

Answer 3

c =3 x 10⁸ ms⁻¹

Question 4

What are the seven types of EM waves

Answer 4

• Radio
• Micro
• Infrared
• Visible
• Ultraviolet
• X-Rays
• Gamma

Question 5

What is the equation for the speed of an EM wave

Answer 5

c = fλ

Question 6

What is the wavlength range for Radiowaves

Answer 6

More than a metre:
10⁻¹ < λ < 10⁶

Question 7

What is the wavlength range for Microwaves

Answer 7

Milimetres to Metre:
10⁻¹ < λ < 10⁻³

Question 8

What is the wavelength range for Infrared

Answer 8

7 x 10⁻⁷ < λ < 10⁻³

Question 9

What is the wavelength range for visible light

Answer 9

4 x 10⁻⁴ < λ < 7 x 10⁻⁷

Question 10

What is the wavelength range for Ultraviolet

Answer 10

10⁻⁸ < λ < 4 x 10⁻⁷

Question 11

What is the wavelength range for X - Rays

Answer 11

10⁻¹⁰ < λ < 10⁻⁸

Question 12

What is the wavelength range for gamma waves

Answer 12

10⁻¹² < λ < 10⁻¹⁰

Question 13

Why does refraction of EM waves only occur iat angles

Answer 13

If transmission occurs normally, the whole wave changes speed at the same time thus negating the differences in wave direction

Question 14

What does the magnitude of refraction depend on

Answer 14

The difference in optical density of both the 1st and 2nd material

Question 15

What is meant by refractive index

Answer 15

A way to quantify the difference in direction of a wave in 2 different mediums, it is calculated by the ratio between the speed of light in a vacuum to the speed of light in a specified medium

Question 16

What is the equation for refractive index

Answer 16

n = c/v
n - Refractive index
c - The speed of light in a vacuum
v - The speed of light in the specified medium

Question 17

Interpret what a refractive index of n means

Answer 17

A refractive index of n means that in the specified medium, light travels n times slower than light in a vacuum

Question 18

What does a refractive index of 1 mean

Answer 18

Light travels the same speed in a vacuum as in the specified medium

Question 19

What can’t the value of refractive index be and why

Answer 19

• Less than one because it would imply that light travels faster in another material than in a vacuum

Question 20

Say light travels from a low to high refractive index medium, what does a higher refractive index imply

Answer 20

A highly optically dense 2nd medium (more particles), meaning the light travels slower in the new medium, meaning that the refracted ray bends towards the normal

Question 21

Say light travels from a high to low refractive index medium, what does a lower refractive index imply

Answer 21

A low optically dense 2nd medium (less particles), meaning the light travels faster in the new medium, meaning that the refracted ray bends away from the normal

Question 22

What is snells law

Answer 22

n₁sin(x₁) = n₂sin(x₂)
n₁ =incident index
n₂ =refracted index
x₁ =incident angle
x₂ =refracted angle

Question 23

What is the equation for the critical angle of a medium

Answer 23

Sin(C) = 1/n
C - critical angle
n - refractive index

Question 24

What is meant by the critical angle

Answer 24

• The angle of incidence when the angle of refraction is equal to 90

Question 25

What are the 2 conditions for total internal reflection

Answer 25

- The angle of incidence should be greater than or equal to the critical angle - The EM radiaton must be travelling from a medium witha high refractive index to a relativelly lower refractive index

Question 26

Derive the equation for critical angle, from a material with refractive index n, to air

Answer 26

n₁sin(x₁) = n₂sin(x₂) n₂ = 1 sin(x₂) = sin(90) = 1 x₁ = C Therefore, sin(C) = 1/n

Question 27

What is the difference between a material with a low and high critical angle

Answer 27

- The material with a lower critical angle, will have a higher proportion of light from all directions that will totally internaly reflect