(3) Waves Unfinished

Question 1

Explain the difference between longitudinal and transverse waves

Answer 1

Transverse waves
* Their vibration is crest to trough to the direction that the energy travels e.g. Light

Longitudinal waves
* The vibration is in the same direction as the energy travels e.g. Sound

Question 2

Know the definitions of amplitude, wavefront, frequency, wavelength and period of a
wave

Answer 2

Amplitude - Difference between the origin and the crest (or trough)
Wavefront - A wavefront is an imaginary surface (line) representing corresponding points of a wave that vibrate in unison. It is the set of all locations in a medium where the wave is at the same phase
Frequency - The number of waves produced by the source each second
Wavelength - The distance between a point on one wave and the same point on the next wave.
Period - The duration for a single oscillation or for an entire wavelength to pass a reference point e.g. time period = 1/frequency

Question 3

Know that waves transfer …… and information without transferring ……

Answer 3

1. Energy
2. Matter

Question 4

Know and use the relationship between the speed, frequency and wavelength of a
wave

Answer 4

wave speed = frequency × wavelength
v = f × λ

Question 5

Use the relationship between frequency and time period

Answer 5

frequency = 1/time period
f = 1/t

Question 6

Use the above relationships in different contexts, including sound waves and
electromagnetic waves e.g frequency = 1/time period

Question 7

Explain why there is a change in the observed frequency and wavelength of a wave
when its source is moving relative to an observer and that this is known as the
Doppler effect

Answer 7

When an object is moving toward an observer, the waves get compressed, resulting in a higher frequency.

Question 8

Explain that all waves can be reflected and refracted

Answer 8

Reflection - Waves bouncing back after hitting a barrier
Refraction - Waves changing speed and direction when passing from one medium to another

Question 9

Know the order of the electromagnetic spectrum in terms of decreasing wavelength
and increasing frequency, including the colours of the visible spectrum

Answer 9

It is the full range of magnetic radiation, organized by frequency or wavelength. It consists of Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray and Gamma ray. This is in the order of biggest wave length to smallest, left -> right.

Question 10

Know that light is part of a continuous ………….. ……. that includes radio,
microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations, and that all
these waves travel at the …. ….. in free space

Answer 10

1. Electromagnetic spectrum
2. same speed

Question 11

Explain some of the uses of electromagnetic radiations

Answer 11

• Radio waves: broadcasting and communications
• Microwaves: cooking and satellite transmissions
• Infrared: heaters and night vision equipment
• Visible light: optical fibres and photography
• Ultraviolet: fluorescent lamps
• X-rays: observing the internal structure of objects and materials, including for
  medical applications
• Gamma rays: sterilising food and medical equipment

Question 12

Explain the detrimental effects of excessive exposure of the human body to
electromagnetic waves and describe simple protective measure against the risks

Answer 12

Effects
* Microwaves: internal heating of body tissue
* Infrared: skin burns
* Ultraviolet: damage to surface cells and blindness
* X-ray: slightly increased risk of cancer, radiation sickness
* Gamma rays: cancer, mutation

Protective Measures
* Microwaves: Use microwave shielding materials, such as reflective aluminum or absorptive conductive foam and rubber.
* Infrared: Glass filters out the thermal imaging wavelenghts, clothes reduce exposure, Ozone layer absorbs infrared light
* Ultraviolet: Ozone layer absorbs harmful UV rays, staying in the shade, clothing that covers the skin, use sunscrean
* Gamma rays: Earths atmosphere, use shielding from the source of gamma radiation.

Question 13

Know that light waves are ………. waves and that they can be ……… and
………

Answer 13

1. transverse
2. reflected
3. refracted

Question 14

Use the law of reflection (the angle of incidence equals the angle of reflection)

Answer 14

Use photo

Question 15

Draw ray diagrams to illustrate reflection and refraction

Answer 15

photo

Question 16

practical: investigate the refraction of light, using rectangular blocks, semi-circular
blocks and triangular prisms

3.17

Answer 16

Make sure i understand it

Question 17

know and use the relationship between refractive index, angle of incidence and angle
of refraction

Answer 17

Refractive index of material =
sin⁡(angle of incidence)/sin⁡(angle of refraction)

Answer 18

Refractive index of material= Speed of light in a vacuum /Speed of light in material

Question 19

practical: investigate the refractive index of glass, using a glass block

Question 20

describe the role of total internal reflection in transmitting information along optical
fibres and in prisms

Answer 20

In optical fibers, total internal reflection traps light in the core, allowing it to travel long distances.
In prisms, total internal reflection is used to control the timing of light pulses and improve signal quality

Question 21

explain the meaning of critical angle

Answer 21

When the angle of refraction is equal to (90°), the angle of incidence is called the critical angle. The angle of refraction cannot be greater than (90°).

Question 22

know and use the relationship between critical angle and refractive index