AP Physics 2 photoelectric effect cheat sheet

Photoelectric effect → Definition

The emission of electrons from a material when it absorbs light or electromagnetic radiation.

What is a photon?

A photon is a quantum of electromagnetic radiation, exhibiting both wave and particle properties.

True or False: All wavelengths can cause photoemission.

False. Only photons with energy greater than the material's work function can cause photoemission.

Work function → Definition

The minimum energy required to remove an electron from the surface of a material, typically measured in electron volts (eV).

Threshold frequency → Definition

The minimum frequency of light required to eject electrons from a material, related to the work function by $\displaystyle f_0 = \\frac{\phi}{h}$.

Cause → Effect of increasing light intensity

Increased number of photons leads to more emitted electrons, but does not affect their kinetic energy.

Kinetic energy of emitted electrons

Given by the equation $\displaystyle KE = hf - \phi$, where $\displaystyle hf$ is the energy of the incoming photon.

Comparison: Classical vs Quantum predictions

Classical physics predicts energy increase with intensity; quantum theory explains energy as quantized, dependent on frequency.

What happens below threshold frequency?

No electrons are emitted, regardless of light intensity or duration.

Photoelectric effect demonstration

Experiments show that light causes electron emission, confirming that light has particle-like behavior.

True or False: Photon energy is frequency dependent.

True. The energy of a photon is directly proportional to its frequency: $\displaystyle E = hf$.

Photons and electron emission

If a photon has energy greater than the work function, it can eject an electron.

Factors affecting photoemission

- Light frequency - Material type - Surface condition

Einstein’s photoelectric equation

$\displaystyle E_{max} = hf - \phi$, where $\displaystyle E_{max}$ is the maximum kinetic energy of emitted electrons.

Fill in the blank: Photoelectric effect confirms light's ______ nature.

particle

Role of the photoelectric effect in technology

Foundational for devices like solar cells, photodetectors, and vacuum tubes.

What is the equation for photon energy?

Photon energy is given by $\displaystyle E = hf$, where $\displaystyle E$ is energy in joules, $\displaystyle h$ is Planck's constant ($\displaystyle 6.626 imes 10^{-34} ext{ J s}$), and $\displaystyle f$ is the frequency in hertz.

Formula for kinetic energy of ejected electrons?

Kinetic energy of ejected electrons is: $\displaystyle KE = E_{photon} - ext{W}$, where $\displaystyle W$ is the work function in joules.

Fill in the blank: Work function (W) is measured in ____.

W is measured in joules (J).

True or False: Increasing light intensity increases photon energy.

False. Increasing intensity increases the number of photons, not their energy.

What is the relationship between frequency and wavelength?

Frequency and wavelength are related by $c = u imes \beta$\displaystyle , where$c$\displaystyle is the speed of light,$ u$\displaystyle is frequency, and$\beta$ is wavelength.

Calculate photon energy for $\displaystyle f = 5 imes 10^{14} ext{ Hz}$.

Using $\displaystyle E = hf$: $\displaystyle E = (6.626 imes 10^{-34} ext{ J s})(5 imes 10^{14} ext{ Hz}) = 3.313 imes 10^{-19} ext{ J}$.

Work function (W) for photoemission from silver?

W for silver is approximately $\displaystyle 4.7 ext{ eV} = 7.52 imes 10^{-19} ext{ J}$.

What happens when photon energy is less than work function?

Electrons are not ejected. $\displaystyle E_{photon} < W$ means no photoelectric effect.

E = hf: what do h and f represent?

$\displaystyle h$ is Planck's constant, $\displaystyle f$ is frequency of the incident light.

Identify the equation for stopping potential (V).

$\displaystyle eV = KE_{max}$, where $\displaystyle e$ is electron charge ($\displaystyle 1.6 imes 10^{-19} ext{ C}$) and $\displaystyle KE_{max}$ is maximum kinetic energy.

How does frequency affect kinetic energy of ejected electrons?

As frequency increases (above threshold), $\displaystyle KE_{max}$ increases linearly: $\displaystyle KE = hf - W$.

Threshold frequency ($\displaystyle f_0$) definition?

The minimum frequency required to eject electrons: $\displaystyle W = hf_0$.

Applications of the photoelectric effect?

- Solar panels - Photomultiplier tubes - Digital cameras - Light sensors

True or False: The photoelectric effect is used in night vision devices.

True. The photoelectric effect enables the conversion of low-level light into a visible image.

Fill in the blank: The photoelectric effect is critical in _______.

photovoltaic cells.

How do solar panels work?

Solar panels convert sunlight into electricity using the photoelectric effect, where photons dislodge electrons.

Comparison: Photovoltaic cells vs. Photomultiplier tubes.

PV cells convert sunlight to electricity; photomultiplier tubes amplify light signals.

What type of light triggers the photoelectric effect most efficiently?

Ultraviolet light. It has higher energy photons that can effectively dislodge electrons.

Cause → Effect: What happens when light hits a metal surface?

Electrons are ejected if the light frequency exceeds the work function.

Example: Photoelectric effect in everyday devices?

Digital cameras use the photoelectric effect to convert light into electrical signals, capturing images.