Section 3: Waves and EM spectrum

Question 1

What is frequency?

Answer 1

Number of complete waves passing a certain point per second.
Measured in Hertz (Hz)

1 Hz is one wave per second or
frequency = 1/time period

Question 2

What is the period of a wave? (time period)

Answer 2

The time it takes for one complete wave to pass a point

Question 3

What is amplitude?

Answer 3

The displacement of the wave from rest to crest

top/bottom from line

Question 4

What is wavelength?

Answer 4

Distance from 2 exact points

e.g from crest to crest

Question 5

What is diffraction?

Answer 5

The spreading out of a wave

• All waves spread out when they pass through a gap or an object
• Amount of diffraction depends on size of gap relative to wavelength of the wave.
• Narrower the gap/longer wavelength, more diffraction
• A narrow gap is about the same as the wavelength of the wave
  1. Gap much wider than wavelength: little diffraction
  2. Gap a bit wider than wavelength: diffraction at edges
  3. Gap same as wavelength: maximum diffraction

Question 6

Longitudinal waves

Answer 6

The vibrations are along the same direction as the wave transfers energy
e.g sound waves and ultrasound, shock waves

Question 7

Transverse waves

Answer 7

The vibrations are at 90° to the direction energy is transferred by the wave
e.g Light and all EM waves, ripples on water

Question 8

Describe the relationship between frequency and wavelength

Answer 8

The higher the frequency, the shorter the wavelength

Question 9

Labe a transverse wave

Answer 9

do it

Question 10

Wave equation

Answer 10

speed = frequency x wavelength
(m/s) (Hz) (m)

v = fλ

(speed of all EM waves are 3 x 10*8 m/s)

Question 11

Draw diffraction of a wave as it

• passes an edge
• passes through a gap

Answer 11

draw it

Question 12

What do waves transfer?

Answer 12

energy and not matter

Question 13

What is the order of the EM spectrum in order of decreasing wavelength(increasing frequency)?

Answer 13

Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma

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Question 14

What is the EM spectrum?

Answer 14

A continous range of electromagnetic waves

Question 15

What are 2 characteristics of EM waves?

Answer 15

• transverse

- travel at the speed of light: 3 x 10 (*8) m/s

Question 16

Give examples of the uses of EM waves

Answer 16

radio waves: broadcasting + communications
microwaves: cooking + satellite transmissions
infra-red: heaters and night vision
visible light: optical fibre + photography
ultraviolet: fluorescent lamps + killing bacteria in water purification
x-rays: observing the internal structure of objects + materials, medical application
gamma rays: sterilising food + medical equipment

Question 17

What are the effects of these on the body: 
microwaves
infrared
uv
X-rays 
gamma rays 

what protects against this?

Answer 17

microwaves: internal heating of body tissue,
damaging cells if they overheat

infrared: skin burns,
skill cells are damaged by overexposure

uv: damage to surface cells and blindness,
can damage receptor cells in the retina

gamma: cancer, mutation
can cause cells to change arrangement

sunglasses / sun cream

Question 18

What are analogue signals?

draw it

Answer 18

signals which can vary in frequency and amplitude

Question 19

What are digital signals?

draw it

Answer 19

series of pulses consisting of 2 states, ON(1) and OFF(0)

Question 20

Why are digital signals better than analogue?

Answer 20

As signals get transmitted, they become weaker and need to be amplified. Regeneration of digital signals create a clean, accurate copy of the original.

However regeneration of analogue signals also amplify any accompanied noise, which may create errors in the signal.

Question 21

what is the relationship between frequency and time period?

Answer 21

frequency = 1 / time period

f = 1 / T