A2 Physics

Spontaneous Decay

Decay occurs without external influence

Random Decay

It is impossible to predict which individual nucleus will decay or when it decay

Half life

Mean time taken for half of the active nuclei in a radioactive sample to decay

Decay Constant

The probability that an individual nucleus will decay per unit time

Half Life Formula

T_1/2 = ln(2)/lambda

Photon

A quantum of electromagnetic energy

Quantum

Discrete amount of energy

Photoelectric effect

Emission of electrons from a metal surface when electromagnetic radiation is incident/absorbed on the surface

Photoelectron

An electron emitted from a metal surface as a result of the photoelectric effect

Threshold Frequency

The minimum frequency of electromagnetic radiation required to cause photoelectric emission from a metal surface

Threshold Wavelength

The maximum wavelength of electromagnetic radiation that can cause photoelectric emission from a metal surface.

Work function

Minimum energy required to release a photoelectron from the surface of the metal

Electronvolt

Energy transferred when an electron moves through a potential difference of 1 volt

eV → J

x 1.6×10^-19

J → eV

/ 1.6×10^-19

Wave Particle Duality: Electromagnetic radiation

Photoelectric effect is evidence of particle-like behaviour, Diffraction is evidence of wave-like behaviour

Wave Particle Duality: Particles

Electron diffraction is evidence for wave-like behaviour

De Broglie Wavelength

Wavelength associated with a moving particle. lambda = h/p

Emission Line Spectrum

Consists of discrete wavelengths produced when electrons transition from higher energy levels to lower energy levels, emitting photons.

Absorption Line Spectrum

Consists of discrete wavelengths missing from a continuous spectrum because photons of those wavelengths have been absorbed by electrons transitioning from lower to higher energy levels.

Hardness of X-Ray beam

The penetration of the beam

Internal Energy

Sum of the random distribution of kinetic and potential energies within a system of molecules

First Law of Thermodynamics

Increase in internal energy of a system is equal to the sum of the thermal energy added to the system and the work done on it.

When a gas expands

Work is done by the gas, work is negative

When a gas is compressed

Work is done on the gas, positive work done

Electric Charge

A property of an object that gives rise to a force on the body when the body is in an electric field