Resistors: Understanding Resistance and Its Role in A-Level Science

What Is a Resistor?

A resistor is a component that restricts the flow of electrical current in a circuit.

Resistance and Its Formula

Resistance (R)

Resistance is defined by Ohm’s Law:

\[ R = \frac{V}{I} \]

Where:

• \( R \): Resistance (Ω, Ohms)
• \( V \): Voltage (V, Volts)
• \( I \): Current (A, Amperes)

Types of Resistors

Fixed Resistors

Provide a constant resistance value.

Variable Resistors (Potentiometers)

Allow adjustment of resistance in a circuit.

Applications of Resistors

Current Limitation

Used to control the amount of current flowing through a circuit.

Voltage Division

Divide voltage across components in a circuit.

Heating Devices

Resistors convert electrical energy into heat in devices like toasters and heaters.

Example Problem

A \( 9 \, \text{V} \) battery powers a circuit with a \( 3 \, \Omega \) resistor. Find the current.

1. Formula:
   \[ I = \frac{V}{R} \]
2. Substitute Values:
   \[ I = \frac{9}{3} = 3 \, \text{A} \]

Common Mistakes in Resistor Calculations

1. Mixing up voltage and current in Ohm’s Law
2. Forgetting to account for total resistance in series and parallel circuits
3. Ignoring power dissipation in resistors

Practice Questions

1. A \( 12 \, \text{V} \) battery powers a circuit with \( R = 6 \, \Omega \). Calculate the current.
2. Explain the role of resistors in protecting LEDs.
3. Describe how variable resistors are used in volume controls.