Physics 3.5

Physics 3.5 - Modern Physics

Electron volt (eV)

The amount of energy required to move one electron across one volt

Intensity

Quantity of photons; how many photons in a stream

Photoelectric effect

Emission of electrons due to incident light

Photons

Packets (quanta) of electromagnetic radiation

Saturation current

The maximum possible current possible by the photoelectric effect. All emitted electrons travel to the collector

Stopping voltage

The voltage that prevents all electrons from travelling to the collector

Threshold frequency

Frequency of photon that allows an electron to leave the surface

Work function

Amount of energy required to remove an electron from the surface of a solid. Varies between different materials

Planck’s constant

6.67×10^{-34}Js

Rydberg constant

1.097×10^7m^{-1}

Speed of light

3.00×10^8ms^{-1}

Charge on electron

-1.6×10^{-19}C

Mass of proton

1.6726×10^{-27}kg

Mass of neutron

1.6749×10^{-27}kg

Alpha particle (\alpha)

Electromagnetic radiation emitted in the form of a helium-4 nucleus; containing two protons and two neutrons

Beta particle (\beta)

Electromagnetic radiation emitted in the form of a high-speed ionising electron.

Positron

A beta particle that is positively charged

Gamma ray (\gamma)

Emission of electromagnetic radiation

Energy of a photon is proportional to…

Frequency

Wave equation

v=f\lambda

Absorption spectrum

Spectrum formed when electrons absorb photons of specific wavelengths

Emission spectrum

Spectrum formed when electrons emit photons of specific wavelengths

Ground state

The lowest energy level

Excited state

When an electron gains energy from a photon and ‘jumps’ up energy levels

Lyman series

Ultraviolet light. n=1

Balmer series

Visible light. n=2

Paschen series

Infrared light. n=3

Brackett series

Infrared light. n=4

Pfund series

Infrared light. n=5

Isotope

Atoms with different amounts of neutrons

Binding energy

Amount of energy required to split a nucleus into individual nucleons

Binding energy per nucleon

Amount of energy required to remove one nucleon from the nucleus

Most stable nucleus

Iron-56

Mass defect

Difference in mass between whole nucleus and the nucleons that make up that nucleus.

Mass-energy equivalence

Mass and energy are equivalent and must be conserved in nuclear reactions according to E=mc²

Strong nuclear force

Force between quarks that holds nucleons together

Quarks

Subnucleonic particles that make up protons and neutrons

Nuclear fission

A large, unstable nucleus splits into smaller, more stable nuclei

Nuclear fusion

Small, unstable nuclei fuse to form larger, more stable nuclei

Fusion and fission both emit energy because…

The binding energy per nucleon increases as the nuclei become more stable. This means that each nucleon has less energy that it had previously, so some energy it emitted