Booklet 2B - Waves (Factual) Flashcards
What is the frequency of a wave?
The number of waves per second.
What is the wavelength of a wave?
Wavelength is the distance from a point on one wave to the same point on the next wave.
What is the period of a wave?
The time it takes one wave to pass a point.
What is the amplitude of a wave?
The distace from the centre of a wave (the line of zero disturbance) to the crest or trough.
What is meant by diffraction?
Diffraction is the bending of waves round an object or through a gap.
What will increase the amount of diffraction?
- Longer wavelengths diffract more
- Narrower gaps cause more diffraction
What is a coherent source?
Waves that have a constant phase relationship.
What is constructive intereference?
This occurs when two waves meet at a point in phase.
This results in a wave of larger amplitude.

What is destructive interference?
Destructive interference occurs when two waves meet at a point exactly 180º out of phase.
This results in smaller amplitude (zero if two waves are identical).
What is the test for a wave?
If it can cause interference.
Describe the interference pattern produced by a monochromatic light source and a double slit.
A series of bright and dark fringes symmetrical about the central, brightest fringe.
What is a minimum?
A point where destructive interference occurs e.g. dark, quiet.
What is a maximum?
A point where constructive interference occurs e.g. bright, loud.
What are the conditions for constructive interference in terms of path difference?
The path difference is a whole number of wavelengths.
(0, 1λ, 2λ, 3λ…)
What are the conditions for destructive interference in terms of path difference?
The path difference is an odd number of half wavelengths.
(½λ, 1½λ, 2½λ…)
What are the advantages of using a grating to produce an interference pattern instead of a double slit?
- Fringes are brighter
- Fringes are sharper
Using a grating how can you increase the spacing between the maxima?
- Use a grating with a smaller slit separation.
- Use a source with a greater wavelength of light
- Move the screen further away
If white light is shone through a grating what does the interference pattern look like?
- The central order maximum will be white
- At every other maximum a spectrum will be produced
- The pattern is symmetrical
- Violet is closest to the centre and red the farthest away
What is refraction?
The change in speed of light (and wavelength) as it enters a different material, which can result in a change in direction.
What is meant by absolute refractive index?
It is the ratio of speed of light in a vacuum/air to the speed of light in the material.
It is also the ratio sinθ1/sinθ2 and λ1/λ2 where medium 1 is a vacuum/air.
Describe an experiment to measure refractive index.
- Setup the equipment as shown.
- Measure the angle in air (θa) and in the medium (θp) for a range of incident angles.
- Calculate the sin of all these angles.
- Plot a graph of sin(θa) versus sin (θp).
- The refractive index n is the gradient of this graph.
What happens to the frequency when a wave enters a different medium?
Frequency doesn’t change - it is constant.
A triangular prism can be used to split white light into a spectrum. Why does this occur?
Higher frequencies have a higher refractive index.
What are the 4 differences in spectra produced by refraction (in a prism) and by a grating?
Prism Grating
One spectrum Many spectra
Produced by Refraction Produced by interference
Red light deviated least Red light deviated most
Spectrum is dim Spectrum is bright



