Electricity, Energy and Waves

Section 1: ELECTRICITY

Electric Current and Charge

• Electric current is the flow of charge (electrons) around a circuit, measured in amperes (A).

• Charge (Q) is measured in coulombs (C).

• The formula to calculate charge is:

  Q=I×t

  Where:
  Q = charge (C),
  I = current (A),
  t = time (s)

Potential Difference and Resistance

• Potential difference (voltage) is the energy transferred per coulomb of charge, measured in volts (V).

• Resistance opposes the flow of current and is measured in ohms (Ω).

• Ohm’s Law:

  V=I×R

Series and Parallel Circuits

• Series: current is the same at every point; total resistance adds up; voltage is shared.

• Parallel: voltage is the same across each branch; total current is split; resistance decreases.

Electrical Power and Energy

• Power (P) is the rate of energy transfer.

  P=V×I and P = I² x R

• Energy transferred (E):

  E=P×t or E=V×Q

• Measured in joules (J) or kilowatt-hours (kWh).

Plug Safety and Wiring

• Live wire (brown): carries voltage to the appliance.

• Neutral wire (blue): completes the circuit.

• Earth wire (green/yellow): safety wire to prevent shocks.

• Fuses and circuit breakers protect users by breaking the circuit if too much current flows.

Section 2: ENERGY

Energy Stores

• Types of energy stores include:

  • Kinetic

  • Gravitational potential

  • Elastic potential

  • Thermal (internal)

  • Chemical

  • Nuclear

• Energy is transferred between stores via: mechanical work, electrical work, heating, and radiation.

Conservation of Energy

• Energy cannot be created or destroyed, only transferred or transformed.

• Some energy is always dissipated as heat (usually into the surroundings).

Calculating Energy Transfers

• Kinetic energy:

  KE=0.5mv²

• Gravitational potential energy:

  GPE=mgh

• Work done:

  W=F×d

• Power (already mentioned) relates to energy:

  P=E/t

Efficiency

• Efficiency is a measure of how well energy is converted into useful output:

  Efficiency = (Useful energy output/Total energy output) x 100

Heat Transfer

• Conduction: transfer through solids (vibrating particles).

• Convection: movement in fluids (liquids/gases) where warm fluid rises and cools.

• Radiation: transfer via electromagnetic waves (can happen in a vacuum).

Thermal Insulation

• Reduces energy transfer by conduction, convection, or radiation.

• Examples: cavity wall insulation, double glazing, loft insulation, reflective surfaces.

Section 3: WAVES

Types of Waves

• Transverse waves: oscillations are perpendicular to wave direction (e.g. light, water waves).

• Longitudinal waves: oscillations are parallel to wave direction (e.g. sound).

Wave Properties

• Key terms:

  • Amplitude: maximum displacement from rest position.

  • Wavelength (λ): distance between two corresponding points on a wave.

  • Frequency (f): number of waves per second (Hz).

  • Wave speed (v):

    v =f × λ

Reflection and Refraction

• Reflection: wave bounces off a surface.

  • Angle of incidence = angle of reflection.

• Refraction: wave changes direction as it enters a different medium.

  • Changes in wave speed cause bending.

  • Denser medium = slower speed = bends towards normal.

Sound Waves

• Longitudinal waves.

• Need a medium to travel – cannot travel through a vacuum.

• Speed varies by medium (faster in solids than air).

• Echoes are reflections of sound.

Electromagnetic (EM) Waves

• All EM waves are transverse, travel at the speed of light in a vacuum (~300,000,000 m/s).

• The EM spectrum (from longest to shortest wavelength):

  • Radio waves

  • Microwaves

  • Infrared

  • Visible light

  • Ultraviolet

  • X-rays

  • Gamma rays

Uses and Dangers of EM Waves

• Radio waves: communication.

• Microwaves: cooking, mobile phones.

• Infrared: heaters, night vision.

• Visible light: seeing, photography.

• Ultraviolet: sterilising, detecting forged banknotes (can cause skin cancer).

• X-rays: medical imaging (can damage cells).

• Gamma rays: cancer treatment (highly penetrating and dangerous in high doses).

Key Revision Tips

• Practice calculations (Ohm’s law, energy equations, wave speed).

• Be confident with circuit diagrams and understanding how current, voltage, and resistance behave in different setups.

• Memorise definitions and wave properties.

• Understand real-life applications (e.g. plug safety, uses of EM waves).

• Use past paper questions to get familiar with data analysis and interpreting graphs or diagrams.