Physics Revision: Radioactivity and Refraction of Light

Vocabulary flashcards covering key terms and concepts from Physics Lesson 1 on Radioactivity and Lesson 2 on the Refraction of Light.

Radioactive decay

The process where unstable nuclei release radiation to become more stable.

Background radiation

Radiation that is always present in the environment, originating from sources like rocks, buildings, Radon gas, food, drinks, and cosmic rays.

Geiger-Muller tube

A device used as a detector and counter to measure radiation.

Alpha ($\alpha$)

A helium nucleus consisting of $2$ protons and $2$ neutrons; it is strongly ionising, has weak penetration, and is stopped by paper or skin.

Beta minus ($\beta^-$)

A fast electron with medium ionising ability and medium penetration; it is stopped by thin aluminium.

Gamma ($\gamma$)

An electromagnetic wave that is weakly ionising but very penetrating; it is stopped by thick lead or concrete.

Half-life

The time taken for half the radioactive nuclei in a sample to decay.

Alpha emission

A nuclear process where the mass number decreases by $4$ and the atomic number decreases by $2$.

Refraction

The change in direction of light caused by its speed changing when moving between different materials.

Normal line

An imaginary line drawn at $90^\circ$ to a surface, used to measure angles of incidence and refraction.

Angle of incidence ($i$)

The angle between the incoming ray and the normal line.

Angle of refraction ($r$)

The angle between the refracted ray and the normal line.

Refractive index ($n$)

A measure of how much light bends, calculated using the equation $n = \frac{\sin(i)}{\sin(r)}$.

Critical angle

The angle of incidence at which the refracted ray travels exactly along the boundary between two materials.

Total Internal Reflection

An effect occurring when light travels from a denser medium to a less dense medium and the angle of incidence is greater than the critical angle, reflecting the light back inside.