Why does a device carrying a larger current at the same potential difference transfer power faster?

More charge passes each second and each coulomb transfers the same energy, so more energy is transferred each second.

Why does a 230 V heater transfer power faster than a 12 V heater carrying the same current?

Each coulomb transfers more energy at the higher potential difference, so more energy is transferred each second.

Two lamps are connected across the same supply and one draws a larger current. Which lamp is brighter, and why?

The lamp drawing the larger current is brighter, because at the same potential difference its power is greater.

Explain why a high-power appliance connected to the mains needs a large current.

Power is current multiplied by potential difference, so with the mains potential difference fixed a large power requires a large current.

Which equation links electrical power, current and potential difference?

Power in watts equals current in amperes multiplied by potential difference in volts.

Edexcel GCSE Combined Science Physics 1SC0

Key Concepts of Physics

Topic overview SI units in physics Multiples and sub-multiples of units Converting units, significant figures and standard form

Motion and Forces

Topic overview Scalar and vector quantities Examples of vectors and scalars, and velocity Speed, distance, time and distance-time graphs Acceleration and the equation v squared minus u squared Velocity-time graphs and free fall Measuring speed in the laboratory, and typical everyday speeds Newton's first law, and investigating force, mass and acceleration Newton's second and third laws Weight, mass and gravitational field strength Reaction time, stopping distance and large decelerations Factors affecting stopping distance and reaction time

Conservation of Energy

Topic overview Gravitational potential and kinetic energy Energy transfer diagrams and conservation of energy Energy stores and closed systems Dissipation and wasteful energy transfer Reducing unwanted energy transfer Calculating efficiency Energy resources and trends in their use

Waves

Topic overview What waves transfer, and the evidence for it Frequency, wavelength, amplitude and period Longitudinal and transverse waves The wave equation Measuring wave speed, and what happens at a boundary Measuring waves in ripple tanks, strings and solids

Light and the Electromagnetic Spectrum

Topic overview Properties of electromagnetic waves Investigating refraction in glass blocks The groups of the electromagnetic spectrum The continuous spectrum, and what our eyes can detect How radiation is generated, and why danger rises with frequency Harmful effects of excessive exposure to radiation Uses of electromagnetic radiation

Radioactivity

Topic overview The atom and the size of atoms Isotopes, atomic number and mass number Relative masses and charges of subatomic particles Electron orbits and energy levels Forming ions, and how the atomic model changed Types of ionising radiation Background radiation and detecting radioactivity Alpha, beta and gamma, and their penetrating power Beta-minus and beta-plus decay Effects of decay on atomic number and mass number Balancing nuclear equations Activity and the becquerel Half-life and the randomness of decay Half-life calculations The dangers of ionising radiation Safety precautions, contamination and irradiation

Energy – Forces Doing Work

Topic overview Energy stores and energy transfer diagrams Changing a system's energy, and measuring work done Work done and the energy changes it causes Gravitational potential and kinetic energy calculations Dissipation and wasted energy Power as the rate of energy transfer The watt, and calculating efficiency

Forces and Their Effects

Topic overview Contact and non-contact forces Vectors and scalars, and reducing friction

Electricity and Circuits

Magnetism and the Motor Effect

Topic overview Magnetic poles, permanent and induced magnets Uses of magnetic materials The magnetic field around a bar magnet Plotting compasses and the Earth's magnetic field The magnetic effect of an electric current Solenoids and electromagnets

Electromagnetic Induction

Topic overview The national grid, and step-up and step-down transformers Transformer power calculations

Particle Model

Topic overview Kinetic theory and differences in density Calculating density, and investigating it Changes of state and internal energy Specific heat capacity Specific latent heat and thermal insulation Investigating the specific heat capacity of water Gas pressure and the motion of particles Absolute zero and the kelvin scale

Forces and Matter

Topic overview Elastic and inelastic distortion Spring constant, and linear and non-linear behaviour Work done in stretching a spring

Electricity and Circuits

Calculating electrical power

2 things to know
Paper 6

Overview

Power as current times potential difference, why larger currents or voltages transfer power faster, the current squared times resistance equation, and calculations from each.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how potential difference and current together decide the power of a heater or lamp, and state the equation for electrical power.

Key term

How is the power transferred by a circuit device related to the current in it and the potential difference across it?

Questions from this subtopic

Each one with the model answer underneath.

1
How is the power transferred by a circuit device related to the current in it and the potential difference across it?
Model answer
The power is the current multiplied by the potential difference.
2
Why does a device carrying a larger current at the same potential difference transfer power faster?
Model answer
More charge passes each second and each coulomb transfers the same energy, so more energy is transferred each second.
3
Why does a 230 V heater transfer power faster than a 12 V heater carrying the same current?
Model answer
Each coulomb transfers more energy at the higher potential difference, so more energy is transferred each second.
4
Two lamps are connected across the same supply and one draws a larger current. Which lamp is brighter, and why?
Model answer
The lamp drawing the larger current is brighter, because at the same potential difference its power is greater.
5
Explain why a high-power appliance connected to the mains needs a large current.
Model answer
Power is current multiplied by potential difference, so with the mains potential difference fixed a large power requires a large current.
6
Which equation links electrical power, current and potential difference?
Model answer
Power in watts equals current in amperes multiplied by potential difference in volts.

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Key Concepts of Physics

Motion and Forces

Conservation of Energy

Waves

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