G482 -- Waves Barebones Flashcards
Explain how Polaroid sunglasses can prevent glare from light reflected from a water surface
- light reflected from water surface is partially plane polarised
- alignment of polaroid lens is at right angles to plane of polarisation of reflected light
- polarised reflected light is not transmitted by polaroid lens
Describe and explain an experiment to demonstrate the polarisation of microwaves.
- place microwave transmitter and receiver facing each other
- place two polarising filters (metal grid with bars ~1cm apart) across path of beam
- observed signal on receiver is maximum intensity when polarising filters are parallel
- the first filter polarises the beam, the beam can pass through the second filter because the plane of polarisation of the beam matches the alignment of the filter.
- rotate polarising filter 90° from parallel to crossed
- observed signal on receiver drops to minimum intensity (zero) when polarising filters are crossed
- the beam cannot pass through the second filter when the plane of polarisation of the beam is at 90° to the alignment of the filter.
State what is meant by constructive interference and destructive interference.
•constructive interference:
If two waves exist at the same point and are in phase, the amplitude of the resultant wave will be the sum of the amplitudes of the individual waves.
•destructive interference: If two waves exist at the same point and are antiphase, the amplitude of the resultant wave will be zero as the waves cancel each other out.
Describe and explain an experiment that demonstrates two-source interference using sound.
- two loudspeakers (about 1m apart) connected signal generator to same signal generator
- walk along observation path to observe sound intensity
- sound waves superpose and create interference pattern
- maximum sound intensity occurs when path difference = n*wavelength and constructive interference occurs
- minimum (zero) sound intensity occurs when path difference = odd number of half wavelengths and destructive interference occurs
Describe and explain an experiment that demonstrates two-source interference using microwaves metal plate.
- direct microwave beam onto two narrow (3 cm) parallel slits in metal plate (typical 6 cm apart)
- move microwave receiver along observation path to observe received signal intensity
- microwaves are diffracted and create interference pattern
- maximum intensity occurs when path difference = n*wavelengths and constructive interference occurs
- minimum (zero) intensity occurs when path difference = odd number of half wavelengths and destructive interference occurs
Describe an experiment to determine the wavelength of monochromatic light using a laser and a double slit
•Young’s Double slit experiment
•shine laser beam on two narrow parallel slits (typical 0.5 mm apart)
•light waves are diffracted and create interference pattern
•observe diffraction pattern on screen approximately 1 m from slits
•measure distance from slits to screen using metre rule - use slits of known spacing (or measure using travelling microscope)
• measure distance from central maximum to first bright fringe using travelling microscope
•maximum intensity occurs when path difference = M and constructive interference occurs
•minimum (zero) intensity occurs when path difference = odd number of half wavelengths and destructive interference occurs
•Lambda = ax / D
Lambda = wavelength of laser light [ m ]
a = spacing between slits [ m ]
x = distance from central maximum to first maximum [ m ]
D = distance from slits to screen [ m ]
Describe the use of a diffraction grating to determine the wavelength of light.
•shine laser beam on diffraction grating (of known spacing)
•light waves are diffracted and create interference pattern
•observe diffraction pattern on (semi—circular) screen approximately 1m from slits
• measure distance from grating to screen using metre rule
•measure angle B from central maximum and 1st order maximum by marking positions of the distraction grating, central maximum and order fringe then using protractor.
•maximum intensity occurs when path difference = nwavelengths and constructive interference occurs
•minimum (zero) intensity occurs when path difference = odd number of haif waveiengths and destructive interference occurs
•nwavelengths = d sine theta
N is order of maximum ino units
d is spacing between slits
theta is angle at which maximum occurs
Explain the advantages of using multigle slits in an experiment to find the wave length of light
- diffraction grating produces sharper spectra than double slit
- distance from central maximum to 1st order maximum is greater
- which allows more accurate measurements to be made
Explain with reference to a progressive wave how a stationary wave is formed.
- wave travels to end and is reflected
- reflected wave superposes with incident wave
- at certain points always destructive interference to produce nodes
- at certain points always constructive interference to produce antinodes
State and explain the equipment used to measure the frequency of a sound wave.
- microphone, to transfer mechanical motion of sound wave to electrical signal
- oscilloscope to display wave form for measurement
