Topic 5 – Light and the electromagnetic spectrum

Question 1

What is total internal reflection?

Answer 1

• When light is completely reflected back at a boundary between two mediums
• It occurs when light meets a less dense medium at an angle of incidence larger than the critical angle

Question 2

What is the critical angle?

Answer 2

The angle of incidence which causes the angle of reflection to be 90 degrees

Question 3

What is specular reflection

Answer 3

When rays are reflected from a smooth surface in a single direction

Question 4

What is diffuse reflection

Answer 4

Reflection from a rough surface wich causes scattering

Question 5

How does a red colour filter work

Answer 5

• A red filter absorbs all wavelengths of light other than those in the red range of the spectrum
• This means only red light passes through the filter

Question 6

What colour does an object appear if all wavelengths are reflected by equal amounts

Answer 6

White

Question 7

What colour does an object appear if all wavelengths are absorbed?

Answer 7

Black

Question 8

What happens to wavelengths of light that aren’t relfected by an opaque object

Answer 8

They are reflected

Question 9

What affects the colour of an opaque object

Answer 9

• Different objects reflect different wavelengths of light by different amounts
• The wavelengths that are most strongly reflected determine the colour

Question 10

What is meant by the term opaque

Answer 10

Not see-through

Question 11

What colour of visible light has the highest frequency?

Answer 11

Blue

Question 12

What colour of visible light has the lowest frequency?

Answer 12

Red

Question 13

What colour of visible light has largest wavelength

Answer 13

Red

Question 14

What colour of visible light has smallest wavelength

Answer 14

Blue

Question 15

How does the focal length of a lens relate to its strength

Answer 15

• Longer focal length - less powerful
• Shorter focal length - more powerful

Question 16

What is the equation for the power of a lens

Answer 16

Power of a lens (Dioptres) = 1 / focal point (metres)
P (D) = 1 / f (m)

Question 17

What is the focal length

Answer 17

The distance between the centre of the lens and its principal focus

Question 18

What is the principal focus in a diverging concave lens

Answer 18

The point where parallel light rays converge after passing through a converging lens

Question 19

What is the principal focus on a diverging lens

Answer 19

The point from which the rays appear to diverge from

Question 20

What type of waves are electromagnetic waves

Answer 20

Transverse

Question 21

What properties are shared by all EM waves

Answer 21

• They are all transverse waves
• They all trravel at speed of light
• They can travel through a vacuum

Question 22

What do electromagnetic waves transfer

Answer 22

Energy

Question 23

What type of spectrum do electromagnetic waves form

Answer 23

A continuous spectrum

Question 24

List the order of the EM spectrum in order of increasing wavelength

Answer 24

Radio, Microwaves, Infrared, Visible Light, Ultraviolet, X-Ray, Gamma

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Question 25

Which EM wave has highest frequency

Answer 25

Gamma waves

Question 26

Which EM wave has highest energy

Answer 26

Gamma waves

Question 27

What range of frequencies off EM waves can be detected by the human eye

Answer 27

400-700 nanometres

Question 28

What happens when radiation strikes an object

Answer 28

It is either transmitted, reflected, refracted or absorbed depending on the wavelength of the radiation

Question 29

Do all bodies emit radiation

Answer 29

Yes

Question 30

What happens to the the wavelength of radiation emitted by an object as temperature increases

Answer 30

The hotter the body the shorter the wavelength of radiation released

Question 31

What is required for a body to be at a constant temperature

Answer 31

It needs to radiate the same average power that it absorbs

Question 32

What is intensity

Answer 32

The power transferred per unit area; it is a measure of energy transferred by a wave

Question 33

What happens if the average power a body radiates is less than the average power that it absorbs

Answer 33

The temperature of the object will decrease

Question 34

What can be said about the rates of emission and absorption for a body increasing in temperature

Answer 34

The body is absorbing radiation faster than it is emitting it

Question 35

What factors affect the temperature of the Earth

Answer 35

* The Earth's rate of absorption and emission of radiation * The amount of reflection of radiation into space

Question 36

Explain the effects of differences in the velocities of electromagnetic waves in different substances

Answer 36

It can cause the EM wave to refract as when EM waves interact with matter, they slow down, the denser the substance, the slower the wave. Different eavelengthd can slow dowb by different amounts (dispersion)

Question 37

How does the Earth's atmosphere affect radiation

Answer 37

Atmosphere largely absorbs or reflects radiation from the sun preventing it from reaching Earth. Some radiation is allowed to pass through and warms Earth

Question 38

What happens to radiation emitted from Earth

Answer 38

It is absorbed and re-emitted in all directions by greenhouse gases causing greenhouse effect which warms Earth

Question 39

Where does radiation originate from

Answer 39

Changes in the nuclei of atom

Question 40

How does the frequency of an em wave relate to its danger

Answer 40

As the frequency increases so does the potential danger

Question 41

What are harmful effects on people of excessive exposure to microwaves

Answer 41

Internal heating of body cells

Question 42

What are harmful effects on people of excessive exposure to infrared

Answer 42

Skin burns

Question 43

What are harmful effects on people of excessive exposure to ultraviolet

Answer 43

Damage to surface cells and eyes, leading to skin cancer and eye conditions

Question 44

What are harmful effects on people of excessive exposure to x-rays and gamma rays

Answer 44

Mutation or damage to cells in body

Question 45

What are the uses of radio waves

Answer 45

* Broadcasting * Communications * Satellite transmissions

Question 46

What are the uses of microwaves

Answer 46

* Cooking * Communications * Satellite transmissions

Question 47

What are the uses of infrared

Answer 47

* Cooking * Thermal imaging * Short range communications * Optical fibres * Telivision remote controls * Security Systems

Question 48

What are the uses of visible light

Answer 48

* Vision * Photography * Illumination

Question 49

What are the uses of ultraviolet

Answer 49

* Security marking * Fluorescent lamps * Detecting forged bank notes * Disinfecting water

Question 50

What are the uses of x-rays

Answer 50

* Observing internal structure of objects * Airport security scanners * Medical x-rays

Question 51

What are the uses of gamma rays

Answer 51

* Sterilising food * Medical equipment * Detection of cancer * Treating cancer

Question 52

What causes changes in atoms and nuclei

Answer 52

Absorption of a range of frequencies

Question 53

How can radio waves be produced

Answer 53

Oscillations in electrical circuits

Question 54

How can radio waves create an alternating current in a circuit

Answer 54

When radio waves are absorbed, they can induce oscillations in a circuit with same frequency as waves themselves

Question 55

Can radio waves induce oscillations in electrical circuits

Answer 55

Yes