Explain simple harmonic motion
- Periodic motion in which the restoring force is proportional to the displacement
- E.g. Mass on springs, swinging pendulums
Explain resonance
- When the input frequency matches the natural frequency = vibrate more, resonance increases amplitude
- You can increase the amplitude of a wave by making it oscillate (vibrate) at the right frequency.
Explain Doppler shift
- The difference between the transmitted and received frequencies
- Sound moves towards you = higher pitch
If electromagnetic wave moves towards you = shifted to blue end
Explain polarisation
- Planes of reflection are restricted to one plane
- Only transverse waves can be polarised
- Reflected light = partially polarised
- Aerials pick up polarised signals (radio wave at right angle)
- Materials like crystals can polarise light
- Light = naturally unpolarised
Explain how polarised filters work
- When light reflects off something, it becomes horizontally polarised
- Polarising filters remove reflections from surfaces
- Darkens the sky by completely removing reflection of light off tiny water droplets in atmosphere
- Removes some reflection off water
- Acts as colour enhancer
State the laws of reflection
- Angle of incidence = angle of reflection
2. Incident ray, reflected ray and normal are all in the same plane (2D)
Apply the law of reflection to curved surfaces and explain the effects
- 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)
State the laws of refraction
- Light will change speed and direction (if not coming straight on) when it goes from 1 medium into another.
- Light moves quickest in air. It’s changed (bent) in terms of direction due to change in speed
Explain importance of angle approach in refraction
- Wavefront closest to medium (dense object) will slow down.
- Light travels fastest in a vacuum so when it changes speed by entering another medium and travels more slowly, it is refracted.
- Light speeds up, bends away from normal
Light slows down, bends towards normal - 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.
Explain how there is apparent and real depth
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.
Explain how you get total internal reflection
It’s the phenomena that involves the reflection of all the incident light off the boundary.
Two conditions must be met:
- θ incidence > critical θ
- The light is in the more dense medium and the boundary is with the less dense medium (more dense -> less dense)
Using angle of incidence and critical angle, what is reflection and refraction?
- θ incidence = critical θ = 90 degrees
- θ incidence > critical θ = reflection
- θ incidence < critical θ = refraction
What are used of total internal reflection?
- Endoscopes
2. Binoculars and periscopes (reflecting prisms)
Know what the EM spectrum is and be able to explain sources for each
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
What is the photoelectric effect?
- Shine light on photoelectric material and it releases electrons
- Change intensity/amplitude of light on it increases number of electrons and not the energy
- Only affected by the frequency
- Shows wave and ray model didn’t work
- Photon model=light behaves like a packet of energy but with frequencies associated with it
What point sources obey the inverse square law?
Gravitational force, electric field, light, sound, radiation
Source decreases by 1/x^2
Why does radiation data not follow the inverse square law perfectly?
- Even though radioactive decay predictable, still random
- Don’t know what background radiation is
- Don’t know what the errors are
Describe sound as a wave
Frequency = pitch
Amplitude = loudness
Describe light as a wave
Frequency = colour
Amplitude = brightness
What are the refractive index values of VAWG?
1, 1.00, 1.33, 1.5
