Definitions - Waves, Reflections, Refractions

Question 1

Explain simple harmonic motion

Answer 1

1. Periodic motion in which the restoring force is proportional to the displacement
2. E.g. Mass on springs, swinging pendulums

Question 2

Explain resonance

Answer 2

1. When the input frequency matches the natural frequency = vibrate more, resonance increases amplitude
2. You can increase the amplitude of a wave by making it oscillate (vibrate) at the right frequency.

Question 3

Explain Doppler shift

Answer 3

1. The difference between the transmitted and received frequencies
2. Sound moves towards you = higher pitch

If electromagnetic wave moves towards you = shifted to blue end

Question 4

Explain polarisation

Answer 4

1. Planes of reflection are restricted to one plane
2. Only transverse waves can be polarised
3. Reflected light = partially polarised
4. Aerials pick up polarised signals (radio wave at right angle)
5. Materials like crystals can polarise light
6. Light = naturally unpolarised

Question 5

Explain how polarised filters work

Answer 5

1. When light reflects off something, it becomes horizontally polarised
2. Polarising filters remove reflections from surfaces
3. Darkens the sky by completely removing reflection of light off tiny water droplets in atmosphere
4. Removes some reflection off water
5. Acts as colour enhancer

Question 6

State the laws of reflection

Answer 6

1. Angle of incidence = angle of reflection

2. Incident ray, reflected ray and normal are all in the same plane (2D)

Question 7

Apply the law of reflection to curved surfaces and explain the effects

Answer 7

1. • Bowl of spoon good example of curved surfaces.

• Outside bowl simulates a convex mirror reflecting an image.
• Image is smaller and upright because the reflected light rays don’t cross a focal point (real rays won’t meet, virtual rays will)
  2.
• Image reflected from inside bowl of spoon inverted because the light waves intersect at the focal point before being imaged.
• The size depends on how close the object is to the mirror (real rays will meet, virtual rays won’t)

Question 8

State the laws of refraction

Answer 8

1. Light will change speed and direction (if not coming straight on) when it goes from 1 medium into another.
2. Light moves quickest in air. It’s changed (bent) in terms of direction due to change in speed

Question 9

Explain importance of angle approach in refraction

Answer 9

1. Wavefront closest to medium (dense object) will slow down.
2. Light travels fastest in a vacuum so when it changes speed by entering another medium and travels more slowly, it is refracted.
3. Light speeds up, bends away from normal
   Light slows down, bends towards normal
4. Ray only changes direction if it enters the medium at an angle, if it enters the medium head on (angle incidence = 0) it’ll slow down but be undeviated.

Question 10

Explain how there is apparent and real depth

Answer 10

We perceive light to travel in straight lines but it’s been refracted from one medium into another so the refracted wave looks like it’s higher up.

Question 11

Explain how you get total internal reflection

Answer 11

It’s the phenomena that involves the reflection of all the incident light off the boundary.

Two conditions must be met:

1. θ incidence > critical θ
2. The light is in the more dense medium and the boundary is with the less dense medium (more dense -> less dense)

Question 12

Using angle of incidence and critical angle, what is reflection and refraction?

Answer 12

1. θ incidence = critical θ = 90 degrees
2. θ incidence > critical θ = reflection
3. θ incidence < critical θ = refraction

Question 13

What are used of total internal reflection?

Answer 13

1. Endoscopes

2. Binoculars and periscopes (reflecting prisms)

Question 14

Know what the EM spectrum is and be able to explain sources for each

Answer 14

Radio waves:

• Radio antennas
• Satellite dishes
• TV aerials
• Using a conductor and an AC, electrons in conductor vibrate at right frequency to make the EM field around it vibrate, making a radio wave

Microwaves:

• mobile phones
• satellite transmission
• microwave ovens

Infrared:
- All hot objects

Visible:

• everything that reflects a frequency
• chemiluminescence (chemical reactions)
• nuclear fusion
• things that get hot

U.V Rays:
- Sun (fluorescent)

X-rays:
- X-ray machine

Gamma rays:
- Radionuclide

Question 15

What is the photoelectric effect?

Answer 15

1. Shine light on photoelectric material and it releases electrons
2. Change intensity/amplitude of light on it increases number of electrons and not the energy
3. Only affected by the frequency
4. Shows wave and ray model didn’t work
5. Photon model=light behaves like a packet of energy but with frequencies associated with it

Question 16

What point sources obey the inverse square law?

Answer 16

Gravitational force, electric field, light, sound, radiation

Source decreases by 1/x^2

Question 17

Why does radiation data not follow the inverse square law perfectly?

Answer 17

1. Even though radioactive decay predictable, still random
2. Don’t know what background radiation is
3. Don’t know what the errors are

Question 18

Describe sound as a wave

Answer 18

Frequency = pitch

Amplitude = loudness

Question 19

Describe light as a wave

Answer 19

Frequency = colour

Amplitude = brightness

Question 20

What are the refractive index values of VAWG?

Answer 20

1, 1.00, 1.33, 1.5