What is the photoelectric effect?

The generation of light when electrons flow through a wire The emission of electrons from a metal surface when light above a threshold frequency shines on it The absorption of light by an electron, causing it to jump to a higher energy level The reflection of light by a shiny metal surface

What is the threshold frequency in the photoelectric effect?

The frequency at which light becomes visible to the human eye The minimum frequency of light needed to eject an electron from a particular metal — below this frequency, no electrons are emitted regardless of light intensity The maximum frequency of light the metal can emit The frequency above which light damages metal by heating it

Why did the photoelectric effect puzzle classical physicists?

Classical theory correctly predicted the effect — there was nothing puzzling about it Physicists were puzzled because electrons were not yet known to exist Classical wave theory predicted that bright enough light of any frequency should eventually eject electrons — but experiment showed frequency (not frequency) determined whether emission occurred Classical wave theory predicted that bright enough light of any frequency should eventually eject electrons — but experiment showed frequency (not intensity) determined whether emission occurred

How did Einstein explain the photoelectric effect?

Light is a wave, and the frequency determines how hard the waves hit the metal Light consists of photons — discrete packets each with energy E = hf. Each photon can eject one electron if its energy exceeds the work function φ of the metal Electrons inside the metal vibrate in resonance with light of the right frequency High-frequency light heats the metal more efficiently, boiling off electrons

What is the work function (φ) of a metal?

The minimum light intensity needed to produce a photoelectric current The minimum energy required to remove one electron from the metal's surface — the energy that must be overcome by a single photon The amount of work done by the metal in absorbing light The electrical resistance of the metal to electron flow

If you double the intensity of light above the threshold frequency, what happens to the photoelectric current?

The current stays the same — intensity doesn't affect photoelectric emission The current doubles — twice as many photons eject twice as many electrons, but each electron's maximum kinetic energy is unchanged The current doubles and each electron has twice the kinetic energy The current halves — more light overwhelms the metal's ability to emit electrons

Light of frequency 8 × 10¹⁴ Hz shines on a metal with work function 3.0 × 10⁻¹⁹ J. What is the maximum kinetic energy of ejected electrons? (h = 6.6 × 10⁻³⁴ J·s)

5.28 × 10⁻¹⁹ J 3.0 × 10⁻¹⁹ J 2.28 × 10⁻¹⁹ J 8.28 × 10⁻¹⁹ J

For which achievement did Einstein receive the Nobel Prize in Physics in 1921?

His discovery of the theory of special relativity His explanation of the photoelectric effect — not for relativity, as is commonly assumed His derivation of E = mc² His invention of the laser

The photoelectric effect demonstrates light has particle properties. Does this mean light is not a wave?

Yes — the photoelectric effect proves once and for all that light is particles, not waves No — light is both. It shows wave behaviour (interference, diffraction) and particle behaviour (photoelectric effect, Compton scattering). This is wave-particle duality. Light is neither wave nor particle — these are just rough approximations Light is a wave, and the photoelectric effect is actually explained by classical wave theory

How do solar cells use the photoelectric effect to generate electricity?

Sunlight heats the semiconductor, which thermally expands and drives a turbine Photons with energy above the semiconductor's band gap eject electrons, which flow as an electrical current through an external circuit Light is reflected off the solar panel into a battery, charging it by electromagnetic induction Gamma rays from sunlight ionise the semiconductor, freeing massive numbers of electrons