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# Resistors

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GCSE    Resistors    Questions 0 to 27   -->  View All
• Resistors oppose the free flow of current in a circuit. The current is reduced.
• Resistance is measured in Ohms.

Nick Reeder's Resistor Challenge

## A Simple Circuit

In this simple circuit, the resistor limits the current to a small steady safe level. The switch also has resistance; either zero (on) or infinity (off).

## What Resistors Do

• Resistors limit the current flowing to a smaller safe level.
• Two or more resistors can be used as a voltage divider.
• Voltage dividers can use fixed resistors.
• Voltage dividers can use thermistors or LDRs to make temperature or light sensors.
• Voltage dividers can use potentiometers to make angle sensors.
• Voltage dividers can use potentiometers to make volume controls, dimmers, speed controllers and radio control inputs.
• A timing resistor is used in conjunction with a capacitor to make a timing circuit.
• A pull-up resistor increases the voltage, usually close to the positive power supply voltage.
• A pull-down resistor drops the voltage close to zero or perhaps to the negative power supply voltage.

## A Short Circuit

Without a current limiting resistor, the current is very large and possibly dangerous. There is a fire risk. This is called a short circuit.

## Don't Try This at Home

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