Physics - 2.5 - Wave Particle Duality

When does photoemission take place?

When ultraviolet radiation shines onto a negatively charged metal.

What is the photoelectric effect?

The emission of electrons from a metal due to the effect of electromagnetic radiation.

How can the photoelectric effect be demonstrated?

Using a gold leaf electroscope, which is used to measure small amounts of charge. The angle between the leaf and support is an indication of the amount of charge on the electroscope.

How can a charged electroscope be discharged?

By connecting the metal cap to earth, or bringing a flame close to the metal cap, which ionises the air around it.

How can a negatively charged electroscope be discharged?

Shining a light source with a high enough frequency onto the electroscope.

What does the photoelectric effect depend on?

The type of metal used, the type of radiation and the irradiance (intensity of the radiation).

How can the photoelectric effect be explained?

Light behaves like a particle, the energy of these particles (photons) is related to the frequency of the radiation.

What is a photon?

A particle of electromagnetic radiation.

Does a photon of white light have enough energy to cause photoemission?

No.

What does a higher irradiance mean for the rate of photoemission (current)?

It will increase the rate at which electrons are removed.

How many electrons can one photon remove?

One electron.

If the photons do not have enough energy, what effect will increasing the irradiance have?

It will have no effect.

What is threshold frequency?

The minimum frequency of electromagnetic radiation for which photoemission will occur for a particular substance.

What is the symbol for threshold frequency?

f₀

What is the work function?

The minimum energy (per photon) required to remove an electron from a metal.

What is the symbol for the work function?

W = hf₀

What is h?

Planck’s constant.

What is the equation for the energy of a photon? E = …

E = hf (f = frequency of radiation)

The energy of a photon is directly proportional to its …

frequency.

What does wave particle duality refer to?

That light acts like both particles and waves.

What is the equation for the work function? W =

W = hf₀

The work function is directly proportional to the …?

The threshold frequency.

Why is it easier to remove electrons from some metals than others?

Different metals have different work functions.

The lower the work function, the lower the …

threshold frequency.

What is one use of the photoelectric effect.

Exposure metres in cameras.

What does the kinetic energy of an electron after it has been ejected depend on?

The difference between the work function and the energy of the photon.

What is the kinetic energy of an electron equal to?

The energy of the photon minus the work function.

E_k = …

E_k = E - W