GCSE AQA Physics P4

Describe the plum pudding model of the atom

A ball of positive charge with negative electrons embedded inside

What experiment disproved the plum pudding model?

Alpha particle scattering experiment

What three conclusions were drawn from the alpha particle scattering experiment?

Mass is concentrated in a tiny nucleus, the nucleus is positively charged, and most of the atom is empty space

How did Niels Bohr adapt the nuclear model?

Proposed that electrons orbit the nucleus at specific energy levels (shells)

Which subatomic particle did James Chadwick discover?

The neutron

What is radioactive decay?

A random process where unstable nuclei emit radiation to become stable

What is the activity of a radioactive source?

The rate at which a source of unstable nuclei decays, measured in Becquerels (Bq)

What is count-rate?

The number of radioactive decays recorded per second by a detector like a Geiger-Muller tube

What is an alpha particle?

Two protons and two neutrons, equivalent to a helium nucleus

What is a beta particle?

A high-speed electron emitted from the nucleus when a neutron turns into a proton

What is a gamma ray?

Electromagnetic radiation emitted from the nucleus

What is the penetration ability of an alpha particle?

Weakly penetrating

What is the penetration ability of a beta particle?

Moderately penetrating

What is the penetration ability of a gamma ray?

Highly penetrating

Which type of nuclear radiation is the most strongly ionising?

Alpha radiation

What is radioactive half-life?

The time taken for half the unstable nuclei in a sample to decay or for the activity to halve

What is radioactive contamination?

The unwanted presence of materials containing radioactive atoms on or inside other materials

What is irradiation?

Exposing an object to nuclear radiation without making the object radioactive

What is nuclear fission?

The splitting of a large, unstable nucleus into two smaller daughter nuclei, releasing neutrons and energy

What is a chain reaction in nuclear fission?

Neutrons released from one fission event trigger further fission events in surrounding nuclei

What is the purpose of control rods in a nuclear reactor?

To absorb excess neutrons and control the rate of the chain reaction

What is nuclear fusion?

The joining of two light nuclei to form a heavier nucleus, releasing energy

Where does nuclear fusion naturally occur?

In the core of stars like the Sun

Why is nuclear fusion difficult to achieve on Earth?

Requires extremely high temperatures and pressures to overcome electrostatic repulsion between positive nuclei