Waves Flashcards
(35 cards)
What is the standard answer to how standing waves are formed?
- Two waves travel in opposite directions (1)
- They interfere (1)
- At any point, if they are in phase, they constructively interfere (1)
- And if they are out of phase, they destructively interfere (1)
- Constructive interference creates antinodes, and destructive interference creates nodes (1)
- Nodes are points of minimum amplitude, and antinodes are points of maximum amplitude (1)
When referring to how a wave travels, always remember to…
… mention they TYPE of wave and the DIRECTION of oscillations compared to direction of energy transfer.
What is the displacement of particles in compression and rarefaction?
Zero
What’s the wavelength of a radio wave?
> 1 x 10^-1
What’s the wavelength of a microwave?
1 x 10^-3 - 1 x 10^-1
What’s the length of an infrared wave?
7 x 10-7 - 1 x 10-3
What’s the length of a visible light wave?
4 x 10-7 - 7 x 10-7
What’s the length of a UV wave?
1 x 10-8 - 4 x 10-7
What’s the length of an X-ray?
1 x 10-11 - 1 x 10-8
What’s the length of a gamma ray?
< 1 x 10-11
How does frequency affect diffraction of sound waves around a corner?
The lower the frequency, the more diffraction (as the smaller the frequency, the larger the wavelength, which is closer to the infinite slit size.
Does total internal reflection occur when a wave would be entering a denser or less dense medium?
A less dense one.
How do you calculate distances with lenses?
P = 1/f = 1/u + 1/v
Where u is the object distance (always positive), and v is the image instance (real side positive, virtual side negative)
What is the principal focus?
The point at which parallel light is focussed to by a lens.
What are real and virtual images?
A real image converges on the side of the observer. A virtual image converges on the side of the object.
Compare progressive waves to stationary waves.
- Stationary waves store energy, progressive waves transfer energy.
- The maximum amplitude of each particles oscillation is the same for a progressive wave, but it varies for particles in a stationary wave.
- All particles in stationary waves move in phase, whereas particles in a progressive wave oscillate out of phase.
What is meant by a real and virtual image?
For a real image, the rays leaving the lens converge to a focal point to form an image. The rays pass through the image.
For a virtual image, the rays leaving the lens diverge and don’t meet at a focal point, the rays do not pass through the image.
How can you explain the effect a lens will have on a setup (e.g. a short-sighted eye, or something out of focus)
- Talk about the POWER of the lens being changed (as the power add between lenses: P = P1 + P2 + …)
What are the units of focal power?
D (dioptre)
Looking at two images from the same camera that are zoomed in by different amounts on a distant scene, how can you deduce which has the larger focal length?
- Assume u is relatively constant
- Identify one with greater M
- M = v/u so greater M has greater v
- So focal length is greater for ‘zoomed in’ image
What does the fact that light can polarise tell us about the nature of light waves?
They are transverse (only transverse waves can polarise).
What happens to the polarisation of reflected light, and what are the uses of this?
- Reflected light is partially polarised.
- The effect is used to remove unwanted reflections in photography, and in polaroid sunglasses to remove glare.
What is the polarisation of radio waves?
- Radio waves are polarised, so the rods on the receiving aerial must be aligned with the rods of the transmission aerial for maximum signal strength.
How can you polarise microwaves?
- There wavelengths are too long, so normal polarising filters don’t work.
- Metal grilles are used to polarise microwaves.
- Microwaves are usually polarised anyway when they are transmitted.
