Eduqas A-Level Physics Waves, photons and lasers overview quiz quiz

Longitudinal waves only

Both transverse and longitudinal waves

Neither type

Transverse waves only

It halves

It doubles

It is unchanged

It quadruples

Equal amplitude alone, regardless of the frequencies or phases of the two sources

Coherence: the same frequency and a constant phase difference

Different wavelengths from the two sources, so a wide range of colours can overlap

Incoherent light, where the phase difference between the sources changes randomly

The speed

The wavelength

The frequency

The direction

$30^\circ$

$48^\circ$

$67^\circ$

$42^\circ$

Increases the number of electrons emitted per second

Increases the maximum kinetic energy of the electrons

Lowers the threshold frequency

Has no effect at all

The momentum carried by each incident photon striking the metal surface

The work function, the minimum energy to free an electron

The maximum kinetic energy of the fastest electrons emitted from the metal

The threshold wavelength above which no electrons are emitted at all

The sum of the two energy levels, $E_2 + E_1$, added together

The energy of the lower level only, $E_1$, where the electron ends up

The difference between the two levels, $E_2 - E_1$

Exactly half the energy of the higher level, $\tfrac{1}{2}E_2$

Spontaneous emission produces fully coherent light of a single phase and direction

Stimulated emission needs no excited atoms at all, working from ground-state atoms

Spontaneous emission requires a metastable state to hold the atom before it decays

Stimulated emission produces a photon identical to the one that triggered it

So that more atoms are excited than in the lower state, letting stimulated emission dominate

So that absorption dominates over emission, allowing the beam to be steadily amplified instead

To cool the laser medium so that fewer atoms occupy the higher energy state at any one time

To lengthen the wavelength of the emitted light so it can escape the optical cavity more easily

$\lambda = \frac{h}{m}$

$\lambda = \frac{h}{p}$

$\lambda = hp$

$\lambda = \frac{p}{h}$

Electrons have no mass at all, like photons

Electrons in the beam travel faster than the speed of light

Electrons show wave behaviour (diffraction)

Electrons carry a positive rather than a negative charge