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 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

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Energy – Forces Doing Work

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Electricity and Circuits

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Forces and Matter

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Electricity and Circuits

Current-potential difference graphs for components

2 things to know
Paper 6

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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Waves

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