Glossary
Electromagnetic radiation
A form of energy that propagates through space as waves and also exhibits particle-like properties, encompassing a wide spectrum from radio waves to gamma rays.
Example:
When you use a microwave oven, you're using electromagnetic radiation at a specific frequency to heat your food.
Frequency (of light)
The number of wave cycles (or photon oscillations) that pass a point per unit of time, determining the energy of individual photons.
Example:
A blue laser pointer emits light with a higher frequency than a red laser pointer, meaning each blue photon carries more energy.
Intensity (of light)
The power per unit area carried by light, related to the number of photons incident on a surface per unit time.
Example:
Turning up the dimmer switch on a light bulb increases its intensity, meaning more photons are being emitted per second, but their individual energy (frequency) remains the same.
Maximum kinetic energy ($$K_{\text{max}}$$)
The highest possible kinetic energy of an electron emitted from a photoactive material, determined by the incident light's frequency and the material's work function.
Example:
If very high-frequency UV light hits a metal, the emitted electrons will have a high maximum kinetic energy, allowing them to travel faster.
Particle nature of light
The concept that light can behave as discrete packets of energy called photons, rather than solely as a continuous wave.
Example:
The particle nature of light explains why a single photon can eject an electron, even if the overall light intensity is low, as long as its energy is sufficient.
Photoactive material
A substance, typically a metal or semiconductor, that readily emits electrons when exposed to electromagnetic radiation of sufficient frequency.
Example:
The thin film of cesium in a photodiode acts as a photoactive material, releasing electrons when light hits it to create a current.
Photoelectric effect
A phenomenon where light striking a material causes electrons to be emitted from its surface. It demonstrates the particle-like nature of light.
Example:
Solar panels utilize the photoelectric effect to convert sunlight into electrical energy, where photons knock electrons loose from semiconductor materials.
Photon
A quantum of light or other electromagnetic radiation, representing the smallest discrete packet of energy that can be transferred.
Example:
When you take a picture with your phone, millions of photons from the scene strike the camera's sensor, creating an image.
Planck's constant ($$h$$)
A fundamental physical constant that relates the energy of a photon to its frequency, appearing in the equation $$E = hf$$.
Example:
In the photoelectric effect equation, Planck's constant acts as the proportionality factor, converting the frequency of light into the energy of a single photon.
Quantized nature of light
The principle that light energy is not continuous but exists in discrete, indivisible packets called photons, each with a specific energy proportional to its frequency.
Example:
The fact that light energy comes in specific 'chunks' rather than a smooth flow is evidence of the quantized nature of light, much like stairs instead of a ramp.
Threshold frequency ($$f_0$$)
The minimum frequency of incident light required to eject electrons from the surface of a particular photoactive material. Below this frequency, no electrons are emitted.
Example:
If a metal's threshold frequency is in the ultraviolet range, visible light, no matter how bright, will not cause electrons to be emitted.
Work function ($$\phi$$)
The minimum amount of energy required to remove an electron from the surface of a specific photoactive material. It is a characteristic property of the material.
Example:
Gold has a higher work function than sodium, meaning it requires more energy (higher frequency light) to eject an electron from its surface.