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AQA A-level Physics Resistors

Resistors

This page covers the following topics:

Ohmic conductors are conductors that obey Ohm's Law, therefore there is a linear relationship between current and potential difference. Examples of ohmic conductors are electrical wires and resistors.

Ohmic conductors

A filament lamp heats up as current flows through it in a circuit and lights up. As the temperature of the filament lamp increases, its resistance also increases and thus the current is reduced. Filament lamps do not obey Ohm's Law and thus the voltage across them are not directly proportional to the current through them.

Filament lamps

A diode is an electrical component used in circuits to allow current to only flow in one direction. This allows for the voltage in a circuit to be controlled and for equipment to be protected. The very high resistance of the diode in one direction means that current can only flow through it in the opposite direction, and thus the diode does not obey Ohm's Law. A small voltage is needed across a diode for it to be able to allow current to flow through it.

Diodes

Thermistors are elecrtical components used in circuits to detect temperature changes. The resistance of a thermistor changes with temperature. As the temperature increases, the resistance of a thermistor decreases. Low temperatures will cause a big resistance in the thermistor and thus little current will flow through it, whereas at higher temperatures, the reduced resistance will allow for more current to flow through it.

Thermistors

A light dependent resistors (LDR) is an electrical component whose resistance changes depending on the light intensity falling on it. The resistance of an LDR decreases as the light intensity increases. In low lighting, the resistance will be high and the amount of current flowing through it will be low, whereas in brighter places, the resistance will decrease, allownig for more current to flow through it. LDRs can be used in circuits to detect light changes.

LDRs

1

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Explain what will happen to the current through a fixed resistor if the potential difference is increased.

AQA A-level Physics Resistors Explain what will happen to the current through a fixed resistor if the potential difference is increased.
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2

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A resistor has a potential difference of 8 V across it and a current of 0.5 A through it. Calculate the resistance of the resistor.

AQA A-level Physics Resistors A resistor has a potential difference of 8 V across it and a current of 0.5 A through it. Calculate the resistance of the resistor.
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3

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Explain what is the function of a filament lamp in a circuit.

AQA A-level Physics Resistors Explain what is the function of a filament lamp in a circuit.
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4

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How does the temperature of a filament lamp affect it?

AQA A-level Physics Resistors How does the temperature of a filament lamp affect it?
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5

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Explain the shape of the current against voltage graph for a filament lamp.

AQA A-level Physics Resistors Explain the shape of the current against voltage graph for a filament lamp.
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6

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Explain how a diode only allows current to flow in one direction.

AQA A-level Physics Resistors Explain how a diode only allows current to flow in one direction.
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7

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Is the resistance of a diode constant? Explain.

AQA A-level Physics Resistors Is the resistance of a diode constant? Explain.
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8

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Explain why the graph of current against voltage for a diode does not go through the origin.

AQA A-level Physics Resistors Explain why the graph of current against voltage for a diode does not go through the origin.
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9

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What is the function of LDRs in circuits?

AQA A-level Physics Resistors What is the function of LDRs in circuits?
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10

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Will current flow through an LDR more easily at high or low light intensity?

AQA A-level Physics Resistors Will current flow through an LDR more easily at high or low light intensity?
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