Energy Types, Formulas, and Circuit Principles for Physics

What is energy?

The ability to do work or cause a change.

What is kinetic energy?

Energy an object has because of its motion.

Give the formula for kinetic energy.

KE = ½ × mass × velocity².

What is gravitational potential energy?

Energy stored in an object due to its height in a gravitational field.

Give the formula for gravitational potential energy.

GPE = mass × gravitational field strength × height.

What is elastic potential energy?

Energy stored when an object is stretched or compressed.

Give the formula for elastic potential energy.

E = ½ × spring constant × extension².

What is chemical energy?

Energy stored in chemical bonds of a substance.

Give examples of chemical energy transfer.

Food → kinetic energy in muscles; fuel → thermal energy in engine.

What is thermal energy?

The total kinetic energy of particles in a substance.

What is specific heat capacity?

Energy needed to raise 1 kg of a substance by 1°C.

What is latent heat?

Energy required to change the state of a substance without changing its temperature.

Differentiate between latent heat of fusion and vaporisation.

Fusion = solid ↔ liquid, vaporisation = liquid ↔ gas.

What is the law of conservation of energy?

Energy cannot be created or destroyed, only transferred.

What are some ways energy is transferred?

Mechanically, electrically, by heating, by radiation.

Give an example of useful energy transfer.

Kettle: electrical → thermal in water.

Give an example of wasted energy.

Light bulb: electrical → thermal (wasted).

What is power?

The rate at which energy is transferred.

What is the unit of energy?

Joule (J).

What is the unit of power?

Watt (W).

What is efficiency?

The proportion of input energy that is usefully transferred.

Give an equation for efficiency.

Efficiency = useful energy ÷ total energy × 100%.

What is conduction?

Energy transfer through solids by particle vibrations.

What is convection?

Energy transfer through fluids by particle movement.

What is radiation?

Energy transfer by electromagnetic waves.

Give an example of conduction.

Metal spoon in hot water heats up.

Give an example of convection.

Boiling water circulates.

Give an example of radiation.

Heat from the Sun or a radiator.

Common Misconception: Energy is "used up".

Correction: Energy is never destroyed, only transferred or dissipated.

Common Misconception: Heavier objects have more energy automatically.

Correction: Energy depends on mass, velocity, height, and other factors, not just weight.

Why are energy-efficient devices important?

They reduce wasted energy, save money, and lower environmental impact.

What is electric current?

The flow of electric charge around a circuit.

What particles carry charge in metals?

Electrons.

What is the unit of current?

Amperes (A).

What is potential difference (voltage)?

Energy transferred per unit charge.

What is the unit of potential difference?

Volt (V).

What is resistance?

A measure of how much a component opposes current flow.

Give Ohm's law.

V = I × R.

What is an ohmic conductor?

A component where current is directly proportional to voltage.

How does a filament lamp behave as voltage increases?

Resistance increases due to heating of the filament.

What is a diode?

A component that allows current to flow in only one direction.

What is a light-dependent resistor (LDR)?

Resistance decreases as light intensity increases.

What is a thermistor?

Resistance decreases as temperature increases.

Series circuit: how does current behave?

Same through all components.

Series circuit: how does voltage behave?

Voltage is shared among components.

Parallel circuit: how does current behave?

Current splits across branches.

Parallel circuit: how does voltage behave?

Voltage is the same across all branches.

What is the advantage of parallel circuits?

Each device can operate independently.

What is the disadvantage of series circuits?

If one component fails, the entire circuit stops.

What is direct current (DC)?

Current flows in one direction only.

What is alternating current (AC)?

Current repeatedly changes direction.

What type of current is supplied by mains electricity in the UK?

AC, 230 V, 50 Hz.

What is the function of a live wire?

Carries voltage from the supply.

What is the function of a neutral wire?

Completes the circuit, carries current away.

What is the function of the earth wire?

Safety wire to prevent electric shocks.

What colours are live, neutral, and earth wires?

Live = brown, Neutral = blue, Earth = green/yellow.

Why are plugs insulated?

Plastic prevents electric shock.

Why are wires made of copper?

Copper is a good conductor of electricity.

What is a fuse?

Safety device that melts and breaks the circuit if current is too high.

What is a circuit breaker?

Automatically switches off a circuit if too much current flows; can be reset.

What is the function of a step-up transformer?

Increase voltage, reduce current for efficient transmission.

What is the function of a step-down transformer?

Reduce voltage for safe domestic use.

Why do transformers only work with AC?

They rely on a changing magnetic field.

Why is electricity transmitted at high voltage?

Reduces current, minimizing energy loss as heat.

What is an RCD?

Residual Current Device; trips if current imbalance occurs to protect humans.

Give examples of energy transfer in circuits.

Electrical → thermal, kinetic, light, or sound.

Common Misconception: Current is "used up".

Correction: Current is the same throughout the circuit; energy is transferred.

Common Misconception: Voltage is the same as current.

Correction: Voltage = energy per charge; current = flow of charge.

Common Misconception: Adding batteries always makes bulbs brighter.

Correction: Only if voltage rises without increasing total resistance.

What is matter?

Anything that has mass and takes up space.

What are the three states of matter?

Solid, liquid, gas.

Describe particle arrangement in solids.

Closely packed, regular arrangement, vibrating in place.

Describe particle arrangement in liquids.

Close together, irregular, particles slide past each other.

Describe particle arrangement in gases.

Far apart, random arrangement, move freely at high speeds.

What is density?

Mass per unit volume.

What is the unit of density?

kg/m³.

Give the formula for density.

Density = mass ÷ volume.

What is internal energy?

The total kinetic and potential energy of particles.

What is temperature a measure of?

Average kinetic energy of particles.

What is specific heat capacity?

Energy needed to raise 1 kg of substance by 1°C.

What is specific latent heat?

Energy to change 1 kg of substance state without temperature change.

What is diffusion?

Movement of particles from high to low concentration.

What is Brownian motion?

Random motion of particles in fluids caused by collisions.

What is pressure in gases?

Force per unit area from particle collisions.

What happens to gas pressure if volume decreases?

Pressure increases; particles collide more often.

What happens to gas pressure if temperature increases?

Pressure increases; particles move faster.

What is absolute zero?

0 K; particles have minimum kinetic energy.

Common Misconception: Particles in liquids are stationary.

Correction: They move past each other.

Common Misconception: Heating always increases temperature.

Correction: During state change, temperature is constant.

What is an atom?

Smallest particle of an element retaining chemical properties.

What is a nucleus?

Central part containing protons and neutrons.

What is a proton?

+1 charge, relative mass 1.

What is a neutron?

0 charge, relative mass 1.

What is an electron?

−1 charge, negligible mass.

Define atomic number.

Number of protons in an atom.

Define mass number.

Protons + neutrons.

How to calculate neutrons?

Mass number − atomic number.

Define isotope.

Atoms with same protons, different neutrons.

Give examples of isotopes.

Carbon-12 and Carbon-14.

Why do isotopes have similar chemical properties?

Same electron configuration.