In β⁻ decay, which type of quark transforms, and what does it become?

A down quark changes into an up quark.

In β⁺ decay, which quark transformation occurs?

An up quark changes into a down quark.

Explain why the quark change in β⁻ decay results in the emission of an electron.

When a down quark (charge −⅓e) changes to an up quark (charge +⅔e), the charge difference of +1e must be balanced by emitting an electron (charge −1e) to conserve charge.

Why does β⁺ decay result in the emission of a positron rather than an electron?

When an up quark (charge +⅔e) changes to a down quark (charge −⅓e), the charge decreases by 1e, so a positron (charge +1e) must be emitted to conserve charge.

State the conservation law for electric charge in particle interactions.

Charge is conserved in all particle interactions; the total charge before equals the total charge after.

What happens to the total charge when particles interact or decay?

The total charge remains constant; it is neither created nor destroyed.

AQA A-Level Physics 7408

Measurements and Their Errors

Topic overview Use of SI units and their prefixes Limitation of physical measurements Estimation of physical quantities

Particles and Radiation

Topic overview Constituents of the atom Stable and unstable nuclei Particles, antiparticles and photons Particle interactions Classification of particles Quarks and antiquarks Applications of conservation laws The photoelectric effect Collisions of electrons with atoms Energy levels and photon emission Wave-particle duality

Waves

Topic overview Progressive waves Longitudinal and transverse waves Principle of superposition of waves and formation of stationary waves Interference Diffraction Refraction at a plane surface

Mechanics and Materials

Topic overview Scalars and vectors Moments Motion along a straight line Projectile motion Newton's laws of motion Momentum Work, energy and power Conservation of energy Bulk properties of solids The Young modulus

Electricity

Topic overview Basics of electricity Current–voltage characteristics Resistivity Circuits Potential divider Electromotive force and internal resistance

Further Mechanics and Thermal Physics

Topic overview Circular motion Simple harmonic motion (SHM)Simple harmonic systems Forced vibrations and resonance Thermal energy transfer Ideal gases Molecular kinetic theory model

Fields and Their Consequences

Topic overview Fields Newton's law Gravitational field strength Gravitational potential Orbits of planets and satellites Coulomb's law Electric field strength Electric potential Capacitance Parallel plate capacitor Energy stored by a capacitor Capacitor charge and discharge Magnetic flux density Moving charges in a magnetic field Magnetic flux and flux linkage Electromagnetic induction Alternating currents Transformers

Nuclear Physics

Topic overview Rutherford scattering α, β and γ radiation Radioactive decay Nuclear instability Nuclear radius Mass and energy Induced fission Safety aspects

AstrophysicsOptional topic

Topic overview Astronomical telescope consisting of two converging lenses Reflecting telescopes Single dish radio telescopes, I-R, U-V and X-ray telescopes Advantages of large diameter telescopes Classification by luminosity Absolute magnitude, M Classification by temperature, black-body radiation Principles of the use of stellar spectral classes The Hertzsprung-Russell (HR) diagram Supernovae, neutron stars and black holes Doppler effect Hubble's law Quasars Detection of exoplanets

Medical PhysicsOptional topic

Engineering PhysicsOptional topic

Topic overview Concept of moment of inertia Rotational kinetic energy Rotational motion Torque and angular acceleration Angular momentum Work and power First law of thermodynamics Non-flow processes The p–V diagram Engine cycles Second Law and engines Reversed heat engines

Turning Points in PhysicsOptional topic

Topic overview Cathode rays Thermionic emission of electrons Specific charge of the electron Principle of Millikan's determination of the electronic charge, e Newton's corpuscular theory of light Significance of Young's double slits experiment Electromagnetic waves The discovery of photoelectricity Wave–particle duality Electron microscopes The Michelson-Morley experiment Einstein's theory of special relativity Time dilation Length contraction Relativistic mass and energy

ElectronicsOptional topic

Topic overview MOSFET (metal-oxide semiconducting field-effect transistor)Zener diode Photodiode Hall effect sensor Difference between analogue and digital signals LC resonance filters The ideal operational amplifier Inverting amplifier configuration Non-inverting amplifier configuration Summing amplifier configuration Real operational amplifiers Combinational logic Sequential logic Astables Principles of communication systems Transmission media Time-division multiplexing Amplitude (AM) and frequency modulation (FM) techniques

Particles and Radiation

Applications of conservation laws

4 things to know
Papers 1 and 3

Overview

Checking charge, baryon number, lepton number and strangeness to decide whether an interaction can happen.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How do you verify that baryon number and charge are conserved in a proposed interaction?

Numbers

How do you check lepton number, strangeness and baryon number in an interaction?

Key term

A kaon decays into pions. Explain why this decay must occur via the weak interaction

Key term

In which type of interaction is strangeness conserved?

Questions from this subtopic

Each one with the model answer underneath.

1
In β⁻ decay, which type of quark transforms, and what does it become?
Model answer
A down quark changes into an up quark.
2
In β⁺ decay, which quark transformation occurs?
Model answer
An up quark changes into a down quark.
3
Explain why the quark change in β⁻ decay results in the emission of an electron.
Model answer
When a down quark (charge −⅓e) changes to an up quark (charge +⅔e), the charge difference of +1e must be balanced by emitting an electron (charge −1e) to conserve charge.
4
Why does β⁺ decay result in the emission of a positron rather than an electron?
Model answer
When an up quark (charge +⅔e) changes to a down quark (charge −⅓e), the charge decreases by 1e, so a positron (charge +1e) must be emitted to conserve charge.
5
State the conservation law for electric charge in particle interactions.
Model answer
Charge is conserved in all particle interactions; the total charge before equals the total charge after.
6
What happens to the total charge when particles interact or decay?
Model answer
The total charge remains constant; it is neither created nor destroyed.

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