AQA GCSE FOUNDATION PHYSICS - Calculating Resistance in Circuits

Calculating Resistance in Circuits: A Foundation Physics Guide

This tutorial will guide you through calculating resistance in electrical circuits, focusing on Ohm's Law and practical applications.

Understanding Resistance

Resistance is a property of a material that opposes the flow of electric current. The higher the resistance, the harder it is for current to flow. We measure resistance in ohms (?).

Ohm's Law

Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage applied across its ends, provided the temperature remains constant. This is expressed as:

• V = I * R

Where:

• V is the voltage (measured in volts, V)
• I is the current (measured in amperes, A)
• R is the resistance (measured in ohms, ?)

We can rearrange this formula to find the resistance:

• R = V / I

Practical Calculations of Resistance

Let's look at some examples of calculating resistance in circuits:

Example 1:

A light bulb has a voltage of 12V across it and a current of 0.5A flowing through it. What is the resistance of the light bulb?

Using the formula:

R = V / I
R = 12V / 0.5A
R = 24?

Therefore, the resistance of the light bulb is 24 ohms.

Example 2:

A resistor has a current of 2A flowing through it when a voltage of 6V is applied. What is the resistance of the resistor?

Using the formula:

R = V / I
R = 6V / 2A
R = 3?

Therefore, the resistance of the resistor is 3 ohms.

Key Points:

• Ohm's Law is a fundamental principle in electricity and is essential for understanding and calculating resistance.
• Remember to use the correct units for voltage, current, and resistance when performing calculations.
• By rearranging the formula, you can solve for any of the variables if you know the other two.

Practice:

Try solving these problems using Ohm's Law:

1. A circuit has a 9V battery connected to a resistor. If the current flowing through the resistor is 0.3A, what is the resistance of the resistor?
2. A device has a resistance of 10?. If a voltage of 5V is applied, what is the current flowing through the device?

Remember, practice makes perfect! The more you work with these calculations, the more comfortable you'll become with using Ohm's Law to understand resistance in circuits.