waves and particle nature of light

frequency (Hz)

number of oscillations per unit time

period (s)

time taken to produce 1 wave / oscillation

wave speed (m/s)

rate of movement of the wave

wavelength (λ)

the distance between one point on a wave and the same point on the next cycle

amplitude (m)

the maximum displacement of the wave from the equilibrium position

transverse waves

• the oscillation of particles is at right angles to the direction of energy transfer and the propagation of the wave

• has peaks and troughs at maximum displacement from the equilibrium position

longitudinal waves

• the oscillation of particles is parallel to the direction of energy transfer and the propagation of the wave

• it has compression which are areas of high pressure, and it has rarefactions which are areas of low pressure

coherence

• to get interference patterns the two sources must be coherent

• when the waves have the same wavelength and frequency, and have a fixed phase difference

superposition

occurs when two waves interfere and combine

interference

when two or more waves combine to produce a resultant wave with a new amplitude

constructive interference

• amplitude of resultant waves increases

• occurs when the path difference is a whole number of wavelengths - a crest plus a crest

• path difference = nλ

destructive interference

• amplitude of resultant wave is zero

• occurs when the path difference is half a wavelength out of phase - a crest plus a trough

• path difference = (n+0.5)λ

path difference

the difference in distance that the waves travel to reach the same point (the point of interference)

phase difference (rad)

the difference in distance of 2 similar points on two waves

standing / stationary wave

they are produced by superposition of two progressive waves of equal amplitude and frequency, travelling with the same speed in opposite directions

nodes (N)

on a stationary wave where there is no displacement (destructive interference)

antinodes (A)

on a stationary wave where the displacement has maximum amplitude (constructive interference)

emission line spectrum

produced when an excited electron in an atom moves from a higher to a lower energy level and emits a photon with an energy corresponding to the difference between these energy levels

energy of a photon equation

E = hf

propagation of light in a medium

the energy is absorbed and re-emitted by electrons in the atoms of the material

threshold frequency

the minimum frequency of electromagnetic radiation for which photoelectric emission occurs

photoelectric effect

electrons are emitted (photoelectrons) from the surface of a metal upon the absorption of electromagnetic radiation

work function

the minimum amount of energy required to remove an electron from the surface of a metal

photoelectrons

electrons that have been emitted using photons