SP5 Light and the Electromagnetic Spectrum

Question 1

What is a normal?

Answer 1

A line drawn at right angles to the barrier or mirror in a ray diagram

Question 2

What is a ray diagram?

Answer 2

A way of modelling what happens when light is reflected or refracted

Question 3

Where are the angle of incidence and the angle of refraction measured from?

Answer 3

The normal

Question 4

State the law of reflection

Answer 4

When waves are reflected, the angle of reflection is equal to the angle of incidence

Question 5

What happens to light when it travels through different materials?

Answer 5

It changes speed and direction

Question 6

Define refraction

Answer 6

The change in the direction of a wave at a boundary

Question 7

When is there no change in direction when a light ray hits the boundary?

Answer 7

If it hits the boundary at right angles

Question 8

What is the medium light travels the fastest in?

Answer 8

Air

Question 9

What is the medium light travels the slowest in?

Answer 9

Solids (glass)

Question 10

What happens when light enters into a medium wherein it travels slower than the previous one?

Answer 10

It bends towards the normal

Question 11

What happens when light enters into a medium wherein it travels faster than the previous one?

Answer 11

It bends away from the normal

Question 12

What is total internal reflection?

Answer 12

Sometimes, when light is moving into a less dense material as compared to one it was already in, instead of being refracted, it is reflected inwards

Question 13

When does total internal reflection occur?

Answer 13

The angle of incidence is greater than the critical angle and the incident material is denser than the second material

Question 14

What are the two conditions for total internal reflection?

Answer 14

• angle of incidence > critical angle
• the incident material is denser than the second material

Question 15

What is the critical angle?

Answer 15

The angle of incidence wherein the angle of refraction is 90 degrees

Question 16

Why can luminous objects be seen?

Answer 16

They give off light

Question 17

What is specular reflection?

Answer 17

Reflection from a smooth, flat surface

Question 18

What is total internal reflection used in?

Answer 18

• prisms
• optical fibres

Question 19

Describe a typical image produced from a specular reflection

Answer 19

• upright
• virtual

Question 20

Define diffuse reflection

Answer 20

Instead of forming an image, the reflected light is scattered in all directions

Question 21

What kind of image does a diffuse reflection cause?

Answer 21

• distorted
• no image at all

Question 22

State the colours in order of increasing frequency and decreasing wavelength

Answer 22

• red
• orange
• yellow
• green
• blue
• indigo
• violet

Question 23

When is light absorbed?

Answer 23

When white light shines on an opaque object

Question 24

Give an example of the transmission of a wave at a boundary

Answer 24

Transparent objects, such as glass transmit waves because they barely absorb any light

Question 25

What are filters?

Answer 25

Pieces of transparent materials that absorb some of the colours in white light and transmit a specific colour

Question 26

When does an object appear black?

Answer 26

When it absorbs all wavelengths of visible light

Question 27

What is a lens?

Answer 27

A shaped piece of transparent glass or plastic that refracts light

Question 28

What does the power of a lens describe?

Answer 28

How much it bends light that passes through it

Question 29

Describe a convex lens

Answer 29

- thicker in the middle than it is at the edges - shaped like an almond/ eye

Question 30

What is the focal point of a lens?

Answer 30

The point where all horizontal rays meet after passing through the lens

Question 31

What is the focal length?

Answer 31

The distance between the lens and the focal point

Question 32

What does a convex lens do?

Answer 32

Focuses light inwards

Question 33

What is a convex lens used in?

Answer 33

- magnifying glasses - to correct long-sightedness - binoculars

Question 34

Describe a concave lens

Answer 34

- 'caves' inwards - thinner at the centre as compared to the edge

Question 35

What does a concave lens do?

Answer 35

Spreads light outwards

Question 36

What is a concave lens used for?

Answer 36

To correct short-sitedness

Question 37

How is a concave lens drawn on a ray diagram?

Answer 37

With a straight line with arrows facing inwards

Question 38

How is a convex lens drawn on a ray diagram?

Answer 38

A straight line with arrows on both sides

Question 39

What is a real image?

Answer 39

An image produced on the opposite side of the lens to the object

Question 40

What is a virtual image?

Answer 40

Appear to come from the same side of lens to object

Question 41

What type of waves are electromagnetic waves?

Answer 41

Transverse waves

Question 42

What are common properties amongst all electromagnetic waves?

Answer 42

- transfer energy as radiation from the source of waves to an absorber - can travel through a vacuum - travel everywhere at the same speed: 3x 10^8 m/s

Question 43

What are EM waves with a slightly higher frequency than visible light called?

Answer 43

Ultraviolet

Question 44

What are EM waves with a slightly lower frequency than visible light called?

Answer 44

Infrared

Question 44

What is IR used for?

Answer 44

- electrical heating - cooking food - optical fibres - security cameras - thermal imaging cameras

Question 44

What are the seven groups within the EM spectrum?

Answer 44

- radio waves - microwaves - IR - visible light - UV - X rays - Gamma rays

Question 44

What are radio waves used for?

Answer 44

Communication: eg: broadcasting TV and radio communications and satellite transmissions. They can also induce oscillations in electrical circuits, as well as being produced by oscillations in electrical circuits

Question 45

What waves can be refracted by the atmosphere?

Answer 45

Radio waves

Question 45

What are the uses of microwaves?

Answer 45

- cooking food - communications - satellite comms

Question 45

What waves are harmful to the human body?

Answer 45

Infrared, microwaves, ultraviolet, radio waves, x rays and gamma rays

Question 46

How can a system stay at a constant temperature?

Answer 46

It must absorb the same amount of power as it radiates

Question 47

What is power?

Answer 47

The amount of energy transferred in a certain time

Question 48

What is Earth's temperature dependant on?

Answer 48

- concentration of greenhouse gases - rates of which light and IR radiation are: ---> absorbed by the Earth's surface and atmosphere ---> emitted by the Earth's surface and atmosphere

Question 49

What happens when light and IR radiation are absorbed by the Earth's surface?

Answer 49

- planet's internal energy increases - surface gets hotter - some energy transferred to the atmosphere by conduction and convection

Question 50

What happens when the Earth radiates lower frequency IR radiation?

Answer 50

- some absorbed by greenhouse gases - greenhouse gases emit IR radiation in all directions; some out into space and some back towards earth

Question 51

What is the 'greenhouse effect'?

Answer 51

When the greenhouse gases in the Earth's atmosphere trap heat, warming the Earth's surface

Question 52

What do greenhouse gases do?

Answer 52

Stabilise the surface temperature of the Earth, allowing the planet to sustain life

Question 53

How is temperature affected if a system absorbs more power than it radiates?

Answer 53

It increases

Question 53

What is causing an enhanced greenhouse effect?

Answer 53

Human activities such as deforestation and burning fossil fuels release more carbon dioxide into the atmosphere, which ends up retaining more heat

Question 53

What is the relationship between wavelength and frequency of all EM waves?

Answer 53

Inversely proportional - as wavelength increases, frequency decreases - as frequency increases, wavelength decreases

Question 54

How is temperature affected if a system radiates more power than it absorbs?

Answer 54

It decreases

Question 55

How is the temperature of the Earth maintained?

Answer 55

By the amount of energy received and emmitted by the sun

Question 56

What are the uses of UV?

Answer 56

- disinfectants - security marking - fluorescent lamps - detecting forged bank notes

Question 57

What are the uses of Gamma rays?

Answer 57

- sterilise foods and surgical instruments - detection of cancer - radiotherapy

Question 58

What are the uses of xrays?

Answer 58

- observing the internal structure of objects - airport security scanners - medical x rays

Question 59

What are the dangers of microwaves?

Answer 59

Internal heating of body cells

Question 60

What is the danger of IR?

Answer 60

Skin burns

Question 61

What is the danger of UV?

Answer 61

Damage to surface cells and eyes, which leads to skin cancer

Question 62

What are the dangers of X rays and gamma rays?

Answer 62

Mutations or damage to body cells