The discovery of photoelectricity (A-level only) Flashcards – AQA A-level Physics (7408)

What did Planck propose about energy exchange to explain the black-body spectrum?

Energy is exchanged in discrete amounts, called quanta, rather than arbitrary continuous amounts.

What is the energy of one quantum of radiation of frequency $f$?

$E = hf$, where $h$ is Planck’s constant.

Why is high-frequency black-body emission suppressed at a given temperature?

Higher-frequency quanta have more energy, and exchanges involving these larger amounts are less likely.

How does the observed high-frequency black-body spectrum differ from the classical prediction?

The observed intensity falls, whereas classical physics predicted unlimited high-frequency intensity.

What is the photoelectric effect?

The emission of electrons from a material when electromagnetic radiation falls on its surface.

What happens below the threshold frequency in the photoelectric effect?

No electrons are emitted, regardless of radiation intensity.

What is the delay before photoelectric emission above the threshold frequency?

There is no measurable delay.

How does increasing radiation frequency above the threshold affect the maximum kinetic energy of photoelectrons?

It increases their maximum kinetic energy.

Why does increasing intensity at a fixed frequency increase photoelectron number but not maximum kinetic energy?

More photons arrive per unit time and can release more electrons, but each photon has the same energy.

What does classical wave theory predict about releasing electrons at any radiation frequency?

A sufficiently intense wave or sufficiently long exposure should supply enough energy to release electrons.

What is the energy of a photon of frequency $f$?

$E = hf$

In Einstein’s explanation of the photoelectric effect, how is photon energy transferred to electrons?

One photon transfers its energy to one electron.

What is the work function of a material?

The minimum energy needed to release an electron from the material.

What is Einstein’s photoelectric equation for maximum electron kinetic energy?

$E_{\mathrm{k,max}} = hf - \phi$

How is the threshold frequency $f_0$ related to the work function $\phi$?

$hf_0 = \phi$

What does the photoelectric effect reveal about the nature of electromagnetic radiation?

It provides evidence of its particle-like nature, alongside its wave behaviour.