Physics & Astronomy Lecture Review

100 question-and-answer style flashcards covering key topics from states of matter, heat, waves, optics, electromagnetism, electricity, nuclear physics, and astronomy to support exam revision.

What are the three classical states of matter?

Solids, liquids, and gases.

Which two properties are definite for a solid?

Definite shape and definite volume.

Why do liquids have no fixed shape?

Because their molecules can slide past one another, allowing them to flow and take the shape of their container.

What are two key properties of gases?

No definite shape and no fixed volume; they expand to fill their container and are highly compressible.

In the kinetic particle model, how are molecules arranged in a solid?

Very close together in a regular lattice; they vibrate about fixed positions.

How does Brownian motion provide evidence for the kinetic model?

The random zig-zag motion of suspended particles shows that gas/liquid molecules collide with them, indicating molecular motion.

What is absolute zero in °C?

−273 °C.

State Boyle’s Law in words.

For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume (PV = constant).

Give the Kelvin/Celsius conversion formulas.

T(K) = °C + 273; °C = T(K) − 273.

Define thermal expansion.

The increase in length, area, or volume of a substance when it is heated.

Which state of matter expands the most when heated?

Gases.

Why are metals good thermal conductors?

They contain free (delocalised) electrons that transfer kinetic energy rapidly through the lattice.

Name three everyday applications of thermal expansion.

Mercury thermometers, removing tight jar lids with hot water, expansion gaps in bridges/railways.

Define internal energy.

The total of the kinetic and potential energies of all particles in a substance.

What is specific heat capacity?

The energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K).

During melting or boiling, why does temperature remain constant?

Thermal energy supplied is used to break intermolecular bonds (latent heat) rather than raise kinetic energy.

State the latent heat terms for melting and boiling.

Latent heat of fusion (melting) and latent heat of vaporisation (boiling).

Give two differences between boiling and evaporation.

Boiling occurs at a fixed temperature throughout the liquid; evaporation occurs at any temperature only at the surface.

List three factors that increase the rate of evaporation.

Higher temperature, larger surface area, and greater air movement.

Define thermal conduction.

Transfer of heat through a material without the bulk movement of the material itself.

What is convection?

Heat transfer in fluids by the movement of warmer, less dense regions rising and cooler, denser regions sinking, forming convection currents.

Which surface is the best emitter and absorber of infrared radiation?

A dull (matt) black surface.

How does surface area affect radiation rate?

Larger surface area increases the rate of emission or absorption of thermal radiation.

State the wave equation.

Wave speed v = f λ (frequency × wavelength).

Differentiate transverse and longitudinal waves.

In transverse waves particles vibrate perpendicular to wave direction; in longitudinal waves they vibrate parallel.

Define diffraction.

The spreading of waves when they pass through a gap or around an obstacle.

State the law of reflection.

Angle of incidence equals angle of reflection (i = r).

What happens to light when it passes from a less-dense to a more-dense medium?

It slows down and bends toward the normal (refraction).

What is the critical angle?

The angle of incidence in the denser medium for which the angle of refraction is 90°.

Explain total internal reflection and give one application.

When incidence exceeds the critical angle, all light is reflected back inside; used in optical fibres and periscopes.

What type of lens corrects short-sightedness?

A concave (diverging) lens.

What is dispersion of light?

Separation of white light into its constituent colours due to wavelength-dependent refractive indices.

List the electromagnetic spectrum from longest to shortest wavelength.

Radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.

Give one use and one hazard of microwaves.

Use: mobile phones or satellite TV. Hazard: internal heating of body tissues.

Why are optical fibres suitable for data transmission?

Glass is transparent to visible/infrared light and total internal reflection keeps signals inside the fibre with high bandwidth.

What frequency range is audible to humans?

20 Hz – 20 kHz.

Define ultrasound.

Sound with frequencies above 20 kHz.

Give one industrial or medical use of ultrasound.

Medical imaging of soft tissue, or non-destructive testing of materials, or SONAR depth measurement.

State Coulomb’s law qualitatively.

Like charges repel, unlike charges attract; force depends on the product of charges and inversely on square of separation.

What is an electric field?

A region in which an electric charge experiences a force.

Define electric current.

Rate of flow of charge; charge per second passing a point (I = Q / t).

What is the unit of current?

Ampere (A).

Explain the difference between direct and alternating current.

DC flows in one direction only; AC reverses direction periodically (e.g., 50 Hz mains).

Define electromotive force (e.m.f.).

The energy supplied per unit charge by a power source; the electrical work done on each coulomb.

What is electrical resistance and its unit?

Opposition to current flow; measured in ohms (Ω).

Write Ohm’s Law.

V = I R; current through a conductor is directly proportional to voltage across it at constant temperature.

How does wire length affect resistance?

Resistance is directly proportional to length (R ∝ L).

State the power equation for electrical devices.

Power P = I V (also P = I²R or V²/R).

In a series circuit, how does current behave?

Same current flows through every component.

In a parallel circuit, what is common across all branches?

The potential difference (voltage) is the same across each branch.

State Kirchhoff’s current law at a junction.

Sum of currents entering a junction equals sum leaving it.

Why are household appliances fused?

A fuse melts and breaks the circuit if current exceeds a safe value, preventing overheating and fires.

What is double insulation?

Appliance design where all live parts are covered by two layers of insulating material, eliminating need for an earth wire.

Explain earthing as a safety measure.

Provides a low-resistance path for fault current to flow to ground, causing fuse or breaker to disconnect supply.

State Fleming’s left-hand rule.

For a current-carrying conductor in a magnetic field: Thumb = Force, First finger = Field (N→S), Second finger = Current (+→−).

What three factors increase the size of an induced e.m.f.?

Faster motion, stronger magnetic field, greater number of coil turns.

Describe the function of a split-ring commutator in a DC motor.

Reverses current every half-turn to maintain continuous rotation in the same direction.

What is a transformer?

Device that changes AC voltage using electromagnetic induction between primary and secondary coils.

Give the transformer turns ratio equation.

Vp / Vs = Np / Ns (voltage ratio equals turns ratio).

Why is electrical power transmitted at high voltage?

High voltage means low current for same power, reducing I²R losses in transmission lines.

State the composition and charge of an alpha particle.

2 protons and 2 neutrons; charge +2e (same as a helium-4 nucleus).

What is beta minus (β⁻) decay?

A neutron in the nucleus converts to a proton and an electron; the electron is emitted as a beta particle (charge −1).

How does gamma radiation differ from alpha and beta?

It is an electromagnetic wave with no mass or charge; very penetrating and weakly ionising.

Define half-life.

Time taken for half the nuclei in a radioactive sample to decay (or for activity to fall to half).

Name two common sources of natural background radiation.

Radon gas from rocks/soil and cosmic rays from the Sun.

Give one industrial use of beta radiation.

Monitoring and controlling thickness of materials such as paper or aluminium foil.

Why is lead used for storing radioactive sources?

Lead’s high density and atomic number provide effective shielding against ionising radiation.

What are the two products of nuclear fusion in stars like the Sun?

Helium nuclei and energy (plus neutrinos).

State Newton’s approximate value for the speed of light.

3.0 × 10⁸ m s⁻¹.

What causes the seasons on Earth?

Tilt of Earth’s rotational axis relative to its orbital plane around the Sun.

How long is one complete rotation of Earth?

Approximately 24 hours.

Define a light-year.

Distance light travels in vacuum in one year (~9.5 × 10¹⁵ m).

List the phases of the Moon starting at new moon.

New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent.

Which four planets are terrestrial (rocky)?

Mercury, Venus, Earth, Mars.

What is redshift and what does it indicate?

Increase in observed wavelength of light from distant galaxies, indicating they are moving away (expanding universe).

State Hubble’s Law.

Recessional velocity of a galaxy is proportional to its distance from Earth (v = H₀ d).

What is the current approximate value of Hubble’s constant?

About 2.2 × 10⁻¹⁸ s⁻¹.

What is cosmic microwave background radiation (CMBR)?

Uniform microwave radiation detected from all directions, remnant of the early universe supporting the Big Bang theory.

Describe the life cycle stage after a red giant for a Sun-like star.

It sheds outer layers forming a planetary nebula, leaving behind a white dwarf.

What stellar remnant can result from a supernova of a massive star?

Either a neutron star or a black hole.

Define gravitational field strength dependence on distance.

Field strength decreases with increasing distance from the mass (inverse-square law).

Why do comets move faster when near the Sun?

Conservation of energy: gravitational potential energy converts to kinetic energy at perihelion.

State three factors that increase resistance heating in a wire.

High current, high resistance, long duration (since heat ∝ I²R t).

What is meant by ‘specific latent heat’?

Energy required to change the state of 1 kg of substance without temperature change (fusion or vaporisation).

Give the ideal-gas qualitative relation between temperature and molecular speed.

Average molecular speed is proportional to the square root of temperature and inversely to the square root of molar mass.

Explain the greenhouse effect in simple terms.

Short-wave solar radiation reaches Earth, is absorbed and re-emitted as long-wave infrared, which is partially trapped by greenhouse gases, warming the planet.

Name three greenhouse gases.

Carbon dioxide (CO₂), methane (CH₄), water vapour (H₂O).

State the audible threshold and pain threshold in decibels roughly.

0 dB (threshold of hearing) and about 120–130 dB (threshold of pain).

What does the amplitude of a sound wave determine?

Its loudness (volume).

How is current direction defined in conventional circuit diagrams?

From positive terminal to negative terminal.

Give the formula linking charge, current, and time.

Q = I t.

What is the purpose of a relay?

To allow a low-current circuit to switch on/off a separate high-current or high-voltage circuit using an electromagnet.

Describe electromagnetic induction briefly.

An e.m.f. is induced in a conductor when it experiences a changing magnetic flux or cuts across magnetic field lines.

What is meant by ‘step-up transformer’?

A transformer with more turns on the secondary coil than the primary, increasing the output voltage.

Why are soft-iron cores used in transformers?

They magnetise and demagnetise easily, improving magnetic flux linkage between coils.

Define momentary power loss formula in transmission lines.

Power lost = I² R (due to resistance of the wires).

Give the nucleus symbol for an alpha particle.

⁴₂He or α.

What detector is commonly used for measuring nuclear count rate?

Geiger–Müller tube.

Explain why gamma rays are used to sterilise medical equipment.

Their high penetration kills microorganisms throughout the object without damaging the material.

What safety principle reduces radiation exposure related to time?

Minimise the time spent near the source.