Ohm's Law

Objectives

• Understand the relationship between current, voltage and resistance.

• Be able to describe, qualitatively, how changes in the voltage or resistance will affect the amount of current flowing.

• Be able to select and use the equation voltage = current × resistance to solve numerical problems involving current flowing in a circuit.

Task 1

Discuss with a partner how you would finish these sentences:

• Voltage is .......................

• Current is........................

• Resistance is ..................

• Charge is ........................

Teacher note: an alternative starter task (matching key words to definitions) is available here.

Task 2

Watch and listen as your teacher explains how resistance affects the flow of current in a circuit, using this simulation.

Click to Run

n.b. there is also a local copy stored here.

Task 3

Your teacher will give you a copy of the table below.  Think carefully about what will happen to the current in the circuit in each case.

Discuss with the person next to you what you think will happen, if you are unsure, and write your answers in the table.

Task 4

We need to be able to perform calculations connecting voltage, current and resistance.  The three quantities are connected by an equation known as Ohm's Law.  Write the title "Ohm's Law" in your exercise book, and copy the formula, with the key to explain what each symbol means.

You may find it useful to show the formula in an equation triangle.  Your teacher will show you how to do this, and how to use the equation triangle to rearrange the formula.

Now, try to solve these problems using the formula you have been given.  Your teacher will show you how to do the first few as an example.  Make sure you lay out all your calculations correctly, and remember to give units with your final answers.

Homework/Extension

Using Ohm's Law, complete questions 1 to 3 on the reverse of the "Electrical resistance" sheet.  Make sure you draw a labelled circuit diagram for each one.