What does a straight line through the origin on a graph of current against potential difference show about a component?

It shows that the resistance of the component is constant.

Explain why the resistance of a filament lamp increases as the potential difference across it increases.

A larger current heats the filament, and the hotter lattice ions vibrate more and obstruct the electrons more.

How does the current in a diode depend on the direction of the potential difference across it?

A diode conducts when it is connected one way round and allows almost no current when it is connected the other way round.

What is the resistance of a diode like when it is connected the wrong way round in a circuit?

Its resistance is extremely high, so the current is almost zero.

Edexcel GCSE Physics 1PH0

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 Braking distance, speed and work done

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 Reflection, refraction, transmission and absorption at a boundary

Light and the Electromagnetic Spectrum

Topic overview Reflection, refraction and total internal reflection Why objects appear coloured Lenses, ray diagrams and images Properties of electromagnetic waves Investigating refraction in glass blocks The groups of the electromagnetic spectrum The continuous spectrum, and what our eyes can detect Emitting and absorbing thermal radiation 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 Uses of radioactivity, and how danger depends on half-life The dangers of ionising radiation Safety precautions, contamination and irradiation Radiotherapy, medical tracers and PET scanners Nuclear power and where nuclear energy comes from Fission of uranium-235 and the chain reaction Controlling a reactor and generating electricity Nuclear fusion and how it differs from fission Why fusion needs extreme conditions

Astronomy

Topic overview Weight and gravitational field strength on other bodies The Solar System and the order of the planets How ideas about the Solar System and ways of observing it have changed Orbits of moons, planets, comets and satellites Gravity, orbital speed and stable orbits The Steady State and Big Bang theories Evidence for an expanding Universe The Doppler effect and red-shift in galaxies The life cycle of a star like the Sun The life cycle of stars more massive than the Sun

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 Turning forces and the moment of a force The principle of moments, levers and gears

Electricity and Circuits

Static Electricity

Topic overview Charging by friction, and attraction and repulsion Electrostatic phenomena and earthing Uses and dangers of static electricity Electric fields

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

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Forces and Matter

Topic overview Elastic and inelastic distortion Spring constant, and linear and non-linear behaviour Work done in stretching a spring Atmospheric pressure and pressure in a fluid Force, area and pressure Calculating pressure, and how pressure varies with depth

Electricity and Circuits

Current-potential difference graphs for components

2 things to know
Paper 2

Overview

The straight line for a fixed resistor, the flattening curve for a filament lamp as it heats, and the one-way conduction of a diode.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does the current in a fixed resistor vary with the potential difference across it at constant temperature?

Key term

How does the current in a filament lamp change as the potential difference across it is increased?

Questions from this subtopic

Each one with the model answer underneath.

1
How does the current in a fixed resistor vary with the potential difference across it at constant temperature?
Model answer
The current is directly proportional to the potential difference, so doubling the potential difference doubles the current.
2
What does a straight line through the origin on a graph of current against potential difference show about a component?
Model answer
It shows that the resistance of the component is constant.
3
How does the current in a filament lamp change as the potential difference across it is increased?
Model answer
The current increases, but by smaller and smaller steps as the potential difference rises.
4
Explain why the resistance of a filament lamp increases as the potential difference across it increases.
Model answer
A larger current heats the filament, and the hotter lattice ions vibrate more and obstruct the electrons more.
5
How does the current in a diode depend on the direction of the potential difference across it?
Model answer
A diode conducts when it is connected one way round and allows almost no current when it is connected the other way round.
6
What is the resistance of a diode like when it is connected the wrong way round in a circuit?
Model answer
Its resistance is extremely high, so the current is almost zero.

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Key Concepts of Physics

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Waves

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