2.6 Electromagnetic Waves

Question 1

What are electromagnetic waves?

Answer 1

Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber without the need of a medium

Question 2

Why are electromagentic waves different to mechanical waves?

Answer 2

Electromagnetic waves do not need a medium to travel through

Question 3

What do electromagnetic waves form?

Answer 3

Electromagnetic waves form a continuous spectrum

Question 4

Can electromagnetic waves travel through a vacuum?

Answer 4

Yes

Question 5

What happens to the velocity of electromagnetic waves through a vacuum?

Answer 5

All electromagnetic waves travel at the same velocity through a vacuum as through air

Question 6

At what speed do electromagnetic waves travel at?

Answer 6

3 x 10⁸ m/s

Question 7

How are the waves in the electromagentic spectrum grouped?

Answer 7

The waves in the electromagnetic spectrum are grouped in terms of their wavelength and their frequency

Question 8

What does the energy waves transfer depend on?

Answer 8

The energy waves transfer depends on the wavelength of the waves

Question 9

The shorter the wavelength, the ____________ the energy transferred

Answer 9

The shorter the wavelength, the higher the energy transferred

Question 10

What are the types of electromagnetic waves, going from long wavelengths to short wavelengths

Answer 10

Going from longwavelengths to short wavelengths:

1. Radio Waves
2. Microwaves
3. Infrared
4. Visible Light
5. Ultraviolet
6. X-ray
7. Gamma Ray

Question 11

Which colour has the longest wavelength?

Answer 11

Red

Question 12

Which colour has the shortest wavelength?

Answer 12

Violet

Question 13

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

Answer 13

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

Question 14

Give 2 examples that show the transfer of energy by electromagnetic waves

Answer 14

• Microwave Ovens transfer energy from a microwave source to the food in the oven, which heats it
• Radiant heaters use infrared radiation to transfer energy from the heater to heat the surroundings

Question 15

What happens when electromagnetic waves move from one medium to another

Answer 15

When electromagnetic waves move from one medium to another, the waves might be:
* Transmitted
* Absorbed
* Reflected
* Refracted

Question 16

How does refraction occur?

Answer 16

Refraction occurs when the speed of the wave changes whilst moving from one substance to another, causing a change of direction

Question 17

Why does refraction occur?

Answer 17

Refraction occurs because waves travel different speeds in different mediums

Question 18

What are the rules of refraction?

Answer 18

• The light ray changes direction towards the normal when it travels from air to glass
• The ray changes direction away from the glass when it travels from glass to air

Question 19

How are radio waves produced?

Answer 19

• Radio waves can be produced by oscillations in electrical circuits

Question 20

How are radio waves produced?

Answer 20

• Radio waves can be produced by oscillations in electrical circuits
• This causes the transmitter to produce radio waves with the same frequency of oscillation

Question 21

How are radio waves absorbed?

What happens?

Answer 21

When radio waves are absorbed by a conductor, they induce an alternating current with the same frequency as the radio wave itself, so radio waves themselves can induce oscillations in an electrical circuit

Question 22

Give the 2 ways electromagnetic waves interact with atoms?

Answer 22

Electromagnetic waves are either absorbed or generated by atoms

Question 23

What happens when an electromagnetic wave is absorbed by an atom?

Answer 23

When an electromagnetic wave is absorbed, it can cause an electron to move to a higher energy level

Question 24

What happens when an electron returns or moves down to a lower energy level?

Answer 24

What an electron returns or moves down to a lower energy level, it can generate an electromagnetic wave

Question 25

Where do gamma rays originate from?

Answer 25

Gamma rays originate from changes in the nucleus of an atom

Question 26

Which elecromagnetic waves have hazardous effects on the human body?

Answer 26

* Ultraviolet waves * X-rays * Gamma rays

Question 27

What do the effects of hazardous electromagnetic waves depend on?

Answer 27

The effects depend on the **type of radiation** and the **size of the dose**

Question 28

What is radiation dose?

Answer 28

Radiation dose is a measure of the risk of harm to the body

Question 29

How is radiation dose measured?

Answer 29

Radiation dose in sieverts

Question 30

How many millisieverts in 1 sievert (Sv)

Answer 30

1000 millisieverts (mSv) = 1 sievert (Sv)

Question 31

What are the hazardous effects of ultraviolet waves?

Answer 31

Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer

Question 32

How can humans be protected from ultraviolet waves?

Answer 32

Skin creams can be used to block ultraviolet waves and prevent them from reaching your skin

Question 33

What are the hazardous effects of gamma rays and X-rays?

Answer 33

X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer

Question 34

What are the uses of radio waves? | Why are they suitable for that purpose?

Answer 34

**Television and Radio** - Because they travel long distances before being absorbed - They reflect off the ionosphere in the Earth's atmoshpere so they can be sent across very long distances around the Earth

Question 35

What are the uses of microwaves? | Why are they suitable for that purpose?

Answer 35

**Satellite Communications and Cooking Food** - They pass through the Earth's atmoshpere withour reflection or refraction - They are absorbed by the water molecules in food, which then heat up

Question 36

What are the uses of infrared (waves)? | Why are they suitable for that purpose?

Answer 36

**Electrical heaters, Cooking food, Infrared cameras** - Easily absorbed by surfaces - Emitted by hot objects

Question 37

What are the uses of visible light (waves)? | Why are they suitable for that purpose?

Answer 37

**Fibre optic communications** - Fibre optic cables contain thin strands of glass which reflect visible light inside to carry pulses of light across cables

Question 38

What are the uses of ultraviolet (waves)? | Why are they suitable for that purpose?

Answer 38

**Energy efficient lamps & Sun tanning** -

Question 39

What are the uses of X-rays and gama rays? | Why are they suitable for that purpose?

Answer 39

**Medical imaging and treatments** - They are highly penetrating

Question 40

What are the differences between each colour in the visible light spectrum?

Answer 40

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency

Question 41

What does the colour of an opaque object depend on?

Answer 41

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

Question 42

What happens if all wavelengths are reflected equally in an opqaue object?

Answer 42

If all wavelengths are reflected equally, then the object appears white

Question 43

What happens if all wavelengths are absorbed by an opqaue object?

Answer 43

If all wavelengths are absorbed the objects appears black

Question 44

How do colour filters work?

Answer 44

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

Question 45

How would a surface look red in terms of wavelength?

Answer 45

When the surface absorbs all the wavelengths except for the red component of the white light, which is reflected off the surface

Question 46

If an object transmits light, what could it be known as?

Answer 46

* transparent * translucent