Topic 5 - Light And EM

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 large 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 determines the colour of visible light waves?

Answer 3

The wavelength and frequency of the light waves.

Question 4

What colour of visible light has the highest frequency?

Answer 4

Violet

Question 5

What colour of visible light has the largest wavelength?

Answer 5

Red

Question 6

What is meant by the term “specular reflection”?

Answer 6

Rays are reflected from a smooth surface in a single direction.

Question 7

What is meant by the term “diffuse reflection”?

Answer 7

Reflection from a rough surface which caused scattering of light rays.

Question 8

How does a red colour filter work?

Answer 8

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

Question 9

What is meant by “opaque”?

Answer 9

Not see-through

Question 10

What governs the colour of an opaque object?

Answer 10

Different objects reflect different wavelengths of light by different amounts

The wavelengths that are most strongly reflected determine the colour

Question 11

What happens to the wavelengths of lights that Aren’t reflected by an opaque object?

Answer 11

Wavelengths Absorbed by the object

Question 12

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

Answer 12

White

Question 13

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

Answer 13

Black

Question 14

What types of waves are EM waves.

Answer 14

Transverse

Question 15

What do EM waves transfer?

Answer 15

Energy (not matter)

Question 16

What type of spectrum do EM waves form?

Answer 16

A continous spectrum

Question 17

Order of EM spectrum in terms of increasing wavelength

Answer 17

Smallest:
Gamma
X ray
Uv
Visible 
Infrared
Microwaves
Radio
Largest:

Question 18

Highest frequency EM wave:

Answer 18

Gamma waves

Question 19

Highest ionising EM wave

Answer 19

Gamma waves

Question 20

What properties are all shared by EM waves?

Answer 20

All transverse

All travel at the same speed in a vacuum and air (3x10^8 m/s)

Question 21

What type of waves can be produced by oscillations in an electrical circuit?

Answer 21

Radio waves

Question 22

How can radio waves create and alternating current in a circuit?

Answer 22

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

Question 23

Where do gamma rays originate from?

Answer 23

Changes in the nuclei of atoms

Question 24

What health effects can Ultraviolet waves cause?

Answer 24

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

Question 25

What health effects can X-rays and Gamma rays cause?

Answer 25

They are ionising radiation so can cause mutations in genes.
They can lead to increased risk of developing various cancers.

Question 26

How does electromagnetic radiation affect electron arrangement in atoms?

Answer 26

Absorption or emission of electromagnetic radiation can cause electron arrangement to change. (It can excite electrons up or down energy levels or remove electron from atom)

Question 27

What are the effects of body cells absorbing radiation?

Answer 27

Large amounts can damage cells. Smaller amounts cause mutation, causing cells to divide rapidly, which can lead to cancer.

Question 28

State and explain a use of radio waves

Answer 28

Communications, because radio waves are long wavelength and can travel Long distance without losing quality

Question 29

State and explain a use of microwaves

Answer 29

Cooking, as microwaves are absorbed by and heat water/fat in foods.

Question 30

State and explain uses of infrared radiation

Answer 30

Cooking food (as it transfers thermal energy) infrared cameras, short range communication.

Question 31

State and explain used of visible radiation

Answer 31

Illuminating (seeing) and fibre Optics as they reflect best in glass (other waves have wavelengths that are too long/short).

Question 32

State and explain used of UV

Answer 32

Sterilisation, as it kills bacteria, energy efficient lamps, as it radiates low heat but high energy and sun tanning.

Question 33

State an explain uses of X rays

Answer 33

Medical imaging and treatment because they are very high energy and can easily penetrate body tissues

Question 34

State and explain used of gamma rays.

Answer 34

Gamma rays are used in medical treatments, such as radiotherapy in the treatment of cancer.

Question 35

Which waves of the EM spectrum are regarded as most dangerous?

Answer 35

Gamma and X rays, as they have the highest energy/highly ionising

Question 36

What is the focal length?

Answer 36

Focal length is the distance between lens and focal point.

Question 37

How is the power of lens related to the focal length and the shape of the lens?

Answer 37

Power of the lens = inverse of the focal length

Shorter focal length, greater power.
Thicker lens means shorter focal length, so greater the power.

Question 38

What happens in a converging lense? Draw an Example

Answer 38

In a converging lens, parallel rays of light are brought to a focus. (Focal point/principal focus)
Also know as convex lense

Question 39

What happens to light in a diverging lense? Draw an example

Answer 39

In a diverging lens, parallel rays of light are made to diverge from a point.
Aka concave lens