Photoelectric effect

The photoelectric effect is a phenomenon in physics. Because of the effect, electrons are emitted from matter after energy from electromagnetic radiation like x-rays or visible light is absorbed. The emitted electrons can be called photoelectrons when this happens. The effect is also called the Hertz Effect,^[2][3] because it was discovered by Heinrich Rudolf Hertz, but this name is not used much.
The photoelectric effect takes place when photons have a few eV of energy. If the photon has lots of energy, compton scattering(~keV of energy) or pair production(~MeV) may take place.
If something gives energy to the metal (e.g visible light) , some kind of energy (some colours) could make electrons emit from the metal, but others couldn't. It is because the energy depends upon the frequency(e.g. different colours). E=hf where h is the Planck constant. The smallest frequency which could make electrons emit from the metal is the cutoff frequency or threshold frequency. If you give the metal more energy than hf (if f is the cutoff frequency) electrons from the metal will have Kinetic energy.
The intensity of the light does not affect the electrons of the metal. Increasing the intensity of light will not display the photoelectric effect unless the frequency of light is greater than the threshold frequency.
The photoelectric effect has helped physicists understand the quantum nature of light and electrons. The concept of wave–particle duality was developed because of the photoelectric effect.

In physics, Compton scattering, or the Compton effect, is the name used for what happens to the energy (or frequency or wavelength) of an X-ray or gamma ray photon when it interacts with matter; the wavelength increases (or energy/frequency decreases) as it scatters off electrons. This scattering is one of the main things that happen when gamma rays meet matter. The Compton effect was studied by Arthur Holly Compton in 1923.

Wave-particle duality is a phenomenon in quantum mechanics describing the way photons and electrons act. Both photons and electrons have certain properties which allow them to behave like a wave at times, or a particle at other times. This idea is sometimes dificult to grasp because, although they behave more like a particle at times, and more like a wave at others, electrons and photons are always both waves and particles.