P13- Electromagnetic Waves

Question 1

What is an electromagnetic wave?

Answer 1

An electromagnetic wave is a transverse wave that transfers energy from the source of the wave to an absorber

Question 2

What are some key facts about electromagnetic waves?

Answer 2

Electromagnetic waves form a continuous spectrum

All electromagnetic waves travel at the same volume through a vacuum or air

Question 3

Describe the trend in the electromagnetic spectrum

Answer 3

Electromagnetic waves are grouped on their frequency and wavelength

The wavelength decreases as you move from left to right and frequency increases

Question 4

Describe the electromagnetic spectrum from left to right

Answer 4

left: radio waves
microwaves
infrared
visible light
ultra-violet
x-rays
right: gamma rays

Question 5

Why do humans only detect a limited range of electromagnetic waves?

Answer 5

Humans only detect a limited range of electromagnetic waves because our eyes can onlu detect visible light

Question 6

How does the direction of a wave change when electromagnetic waves travel from a less dense medium to a denser medium?

Answer 6

When waves travel from a less dense medium (air) to a more dense medium (glass) they refract due to a change in wave speed.

When the wave front enters the denser medium, one side of the wave front slows down before the other.

This causes the wave to bend towards the normal.
The wavelength of the waves will also decrease because wave speed and wavelength are directly proportional.

The wave fronts will be closer together

Question 7

How do you draw a normal?

Answer 7

A normal is drawn as a dotted line perpendicular to a wave boundary.

Question 8

When does refraction not occur when a wave enters a new medium?

Answer 8

If waves enter or leave the medium at right angles to the boundary (along the normal) then they do not change direction

Question 9

Describe an experiment to investigate how different surfaces absorb and radiate infrared radiation

Answer 9

1- place leslie cube on a heat resistant matt. Fill it, almost to the top, with boiling water and replace the lid

2-Leave for one minute to allow the surfaces to heat up to the same temperature as the water

3-Use an infrared detector at a measured distance from each surface to measure the temperature (control: use a clamp stand and ruler to ensure accuracy)

Question 10

How are radio waves produced?

Answer 10

Radio waves are produced by oscillations in electrical circuits

Question 11

Describe what happens when radio waves are absorbed and why

Answer 11

When radio waves are absorbed, they may create an alternating current with the same frequency as the radio wave itself

Therefore, radio waves can induce oscillations in an electrical circuit.

Question 12

Describe what happens when changes take place in atoms and their nuclei

Answer 12

Changes in atoms and their nuclei can cause electromagnetic waves to be generated whereas the absorption of an electromagnetic wave can cause changes in atoms e.g
electrons can change energy level

Gamma rays originate from changes in the nucleus of an atom

Question 13

Describe hazardous electromagnetic waves

Answer 13

Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue.

Question 14

How are electromagnetic waves generated when atoms are heated?

Answer 14

Electrons move from one energy level to a higher one when an atoms is heated.

When the electron returns back to its previous energy level, it generates an electromagnetic wave (light)

Question 15

Describe how electromagnetic waves can be emitted and absorbed

Answer 15

Electromagnetic waves can be emitted and absorbed over a wide frequency range

Question 16

Why are ultraviolet waves hazardous?

Answer 16

Ultraviolet waves can cause the skin to age prematurely

They can also increase the risk of skin cancer

Question 17

Why are gamma and x-rays hazardous?

Answer 17

Gamma and x-rays are forms of ionising radiation. This means that they can knock electrons off of atoms when they are absorbed.

This causes the mutation of genes which increases risk of cancer

Question 18

What two things does the damage caused by radiation depend upon?

Answer 18

The damage caused by radiation depends upon:

-the type of radiation

-the dose

Question 19

What is radiation dose and what is it measured in?

Answer 19

Radiation dose is a measure of the risk of harm to the human body when it has been exposed to radiation.

It is measured in sieverts (Sv)

Question 20

How many millisieverts are in one sievert?

Answer 20

There are 1000 millisieverts in one sievert

Question 21

What are the uses of radio waves and why are they suitable for this use?

Answer 21

television and radio:
they can be transmitted over long distances without being absorbed

Radio waves can reflect off of a layer of charged particles in the atmosphere. This allows radio waves to be transmitted in different directions all over the world

Question 22

What are the uses of microwaves and why are they suitable for this use?

Answer 22

satellite communications, heating food:

Microwaves have frequencies which are easily absorbed by molecules in food. This increases the internal energy of molecules causing heating.

Microwaves are also transmitted easily through the atmosphere

Question 23

What are the uses of infrared and why is it suitable for this use?

Answer 23

Electrical heaters and cooking food:

energy of infrared is easily absorbed by the surface of objects

Infrared cameras:

can detect infrared light which is emitted by all objects. This is especially useful to check heat losses from buildings

Question 24

What are the uses of visible light and why is it suitable for this use?

Answer 24

fibre optic communications:

visible light has a short wavelength so it can carry lots of information within fibres to carry TV and radio signals

Question 25

What are the uses of ultraviolet and why is it suitable for this use?

Answer 25

energy efficient light bulbs: ultraviolet light has a short wavelength so it carries more energy than visible light Energy is absorbed by internal surface of the bulb and re-emitted as visible light Sun tanning:

Question 26

What are the uses of x-rays and gamma rays and why are they suitable for these uses?

Answer 26

medical imaging and treatments: they are highly penetrating x-rays can be used to see bones because they are absorbed by dense structures such as bones and transmitted through body tissues. gamma rays can detect cancers

Question 27

How does a lens form an image?

Answer 27

A lens forms an image by refracting light

Question 28

Describe what happens to light in a convex lens

Answer 28

In a convex lens, light is brought into focus, converges, at principal focus

Question 29

What is the distance between the principal focus and the lens called?

Answer 29

The focal length is the distance from the lens to the principal focus

Question 30

Describe the image produced by a concave lens

Answer 30

The image produced by a concave lens is always virtual

Question 31

Describe the symbol for a convex lens

Answer 31

A line with an arrow at either end

Question 32

Describe the symbol for a concave lens

Answer 32

A line with inverted arrows on each end

Question 33

What happens to a ray of light that passes along the normal through a lens?

Answer 33

The central ray passes through the lens without being refracted

Question 34

Describe how to draw a ray diagram for an object more than two focal lengths away from a convex lens

Answer 34

1- draw a line from the top of the object through the centre of the lens without changing direction 2- draw a line from the top of the object. This line runs parallel to the principal axis. When the ray hits the lens, it is refracted through principal focus 3- Where the rays converge is where the image is formed.

Question 35

Describe what the image of an object over two focal lengths from a convex lens will look like

Answer 35

It wll be a real image; on the other side of the lens It will be diminished It will be inverted

Question 36

What will be the properties of an image that is formed of an object between one and two focal lengths from a convex lens?

Answer 36

The image will be real The image will be magnified The image is inverted

Question 37

What do concave lens cause light to do?

Answer 37

A concave lens will cause light to diverge (spread out)

Question 38

Describe how to draw a ray diagram for a concave lens

Answer 38

1- draw ray from top of object passing through centre of lens without changing direction 2-draw ray from top of object moving parallel to the principal focus. When it hits lens, it will be refracted away from boundary. 3- Draw a dotted line to show it refracted ray coming from principal focus 4- Where the lines meet shows the position of the image

Question 39

What are the properties of an image formed from a concave lens?

Answer 39

It will be diminished It will be virtual (on same side as object) It will be upright

Question 40

Describe an equation to calculate the magnification produced by a lens

Answer 40

magnification = image height/ object height

Question 41

Why does magnification have no units?

Answer 41

It is a ratio

Question 42

What are the properties of colours on the visible light spectrum?

Answer 42

Each colour on the visible light spectrum has a different wavelength and frequency left: infrared has the longest wavelength and smallest frequency right: ultraviolet has the shortest wavelength and the highest frequency

Question 43

What is specular reflection?

Answer 43

Specular reflection is reflection from a smooth surface in a single direction.

Question 44

What does reflection from rough surfaces cause?

Answer 44

Reflection from rough surfaces causes scattering. This is called diffuse reflection.

Question 45

What are the two types of reflection?

Answer 45

Specular reflection (smooth) Diffuse reflection (rough)

Question 46

How do colour filters work?

Answer 46

Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)

Question 47

What does the colour of an opaque object depend on?

Answer 47

The colour of an opaque object is determined by which wavelengths of light are more strongly reflected

Question 48

What happens to wavelengths of light that are not reflected by a surface?

Answer 48

Wavelengths of light that are not reflected by a surface are absorbed

Question 49

When will objects appear white?

Answer 49

If all wavelengths of light are reflected equally then an object will appear white

Question 50

When will objects appear black?

Answer 50

Objects appear black when all wavelengths of light are absorbed

Question 51

What material do objects have to be to transmit light?

Answer 51

Objects have to be either translucent or transparent to transmit light.

Question 52

What does it mean for an object to remain at a constant temperature?

Answer 52

The object must be emitting and absorbing radiation at the same rate to stay at a constant temperature.

Question 53

How does the earth gain and emit radiation?

Answer 53

The sun emits short wavelength radiation such as ultraviolet and visible light This radiation travels to earth Some is reflected e.g by clouds whereas remaining radiation is absorbed by earth Earth radiates energy as long wavelength radiation some of which is trapped by greenhouse gases that reflect it back into atmosphere.

Question 54

Describe factors affect how much energy the earth radiates

Answer 54

cloud cover- reflect infrared back to earth and prevent it from being radiated into space