Define the photoelectric effect .

The photoelectric effect is the emission of electrons from the surface of a metal upon the absorption of electromagnetic radiation .

Define photoelectron .

A photoelectron is an electron removed from a metal by the photoelectric effect .

What does the photoelectric effect provide evidence for?

That light is quantised — transferred in discrete packets of energy, or photons.

True or False? Photoelectrons are created by the incoming light rays.

False. The electrons are already present in the metal; the incoming light does not produce them, it only provides the energy needed to release them.

Define threshold frequency .

The threshold frequency is the minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal.

Define threshold wavelength .

The threshold wavelength is the longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal.

Define the work function .

The work function is the minimum energy required to release a photoelectron from the surface of a material.

Define stopping potential .

The stopping potential is the potential difference required to stop photoelectron emission from occurring.

What happens to the stopping potential when the intensity of the incident radiation is increased, at constant frequency?

The stopping potential stays the same — intensity does not affect the maximum kinetic energy of the photoelectrons.

Why do alkali metals, such as sodium and potassium, have threshold frequencies in the visible light region?

The attractive forces between the surface electrons and the positive metal ions are relatively weak , so less energy is needed to release an electron.

True or False? Increasing the intensity of incident radiation increases the maximum kinetic energy of the emitted photoelectrons.

False. Intensity affects the number of photoelectrons emitted (photoelectric current), not their maximum kinetic energy , which depends only on frequency and the work function.

On a graph of maximum photoelectron kinetic energy E kmax against frequency f , what does the gradient represent, and what is the y-intercept?

Gradient = Planck's constant , h Y-intercept = −Φ (the negative of the work function)

What does the x-intercept represent on a graph of E kmax against frequency f ?

The threshold frequency , f 0 .

Why is the maximum kinetic energy of photoelectrons independent of the intensity of the incident radiation?

Each electron can only absorb one photon , so kinetic energy depends only on the frequency of the incident radiation, not the number of photons.

What is the photoelectric current proportional to?

The intensity of the incident radiation.

Increasing the number of photons striking the metal increases the .......... of photoelectrons emitted, not their kinetic energy.

Increasing the number of photons striking the metal increases the number of photoelectrons emitted, not their kinetic energy.

True or False? Increasing the frequency of incident light while keeping the intensity constant increases the photoelectric current.

False. At constant intensity, increasing the frequency means each photon has more energy , so fewer photons are needed, reducing the number of photoelectrons emitted and hence the current.

A LevelPhysicsCambridge (CIE)Flashcards22. Quantum PhysicsPhotoelectric Effect

Photoelectric Effect (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontThe Photoelectric Effect: Basics
Define the photoelectric effect.

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Cards in this collection (20)

Define the photoelectric effect.
The photoelectric effect is the emission of electrons from the surface of a metal upon the absorption of electromagnetic radiation.
Define photoelectron.
A photoelectron is an electron removed from a metal by the photoelectric effect.
What does the photoelectric effect provide evidence for?
That light is quantised — transferred in discrete packets of energy, or photons.
How many photons can a single electron absorb in the photoelectric effect?
Only one photon.
True or False?
Photoelectrons are created by the incoming light rays.
False.
The electrons are already present in the metal; the incoming light does not produce them, it only provides the energy needed to release them.
Define threshold frequency.
The threshold frequency is the minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal.
Define threshold wavelength.
The threshold wavelength is the longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal.
Define the work function.
The work function is the minimum energy required to release a photoelectron from the surface of a material.
Define stopping potential.
The stopping potential is the potential difference required to stop photoelectron emission from occurring.
State the equation for the maximum kinetic energy of photoelectrons in terms of stopping potential.
$E_{k m a x} = e V_{s}$
What happens to the stopping potential when the intensity of the incident radiation is increased, at constant frequency?
The stopping potential stays the same — intensity does not affect the maximum kinetic energy of the photoelectrons.
Why do alkali metals, such as sodium and potassium, have threshold frequencies in the visible light region?
The attractive forces between the surface electrons and the positive metal ions are relatively weak, so less energy is needed to release an electron.
True or False?
Increasing the intensity of incident radiation increases the maximum kinetic energy of the emitted photoelectrons.
False.
Intensity affects the number of photoelectrons emitted (photoelectric current), not their maximum kinetic energy, which depends only on frequency and the work function.
State the photoelectric equation.
$h f = Φ + \frac{1}{2} m v_{m a x}^{2}$
On a graph of maximum photoelectron kinetic energy E_kmax against frequency f, what does the gradient represent, and what is the y-intercept?
- Gradient = Planck's constant, h
- Y-intercept = −Φ (the negative of the work function)
What does the x-intercept represent on a graph of E_kmax against frequency f?
The threshold frequency, f₀.
Why is the maximum kinetic energy of photoelectrons independent of the intensity of the incident radiation?
Each electron can only absorb one photon, so kinetic energy depends only on the frequency of the incident radiation, not the number of photons.
What is the photoelectric current proportional to?
The intensity of the incident radiation.
Increasing the number of photons striking the metal increases the .......... of photoelectrons emitted, not their kinetic energy.
Increasing the number of photons striking the metal increases the number of photoelectrons emitted, not their kinetic energy.
True or False?
Increasing the frequency of incident light while keeping the intensity constant increases the photoelectric current.
False.
At constant intensity, increasing the frequency means each photon has more energy, so fewer photons are needed, reducing the number of photoelectrons emitted and hence the current.

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