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Rogue Physicist.  Free resources for physics education © 2006-2016 Dorian Pascoe.  Email: dorian.pascoe@hotmail.co.uk

Most resources are available under a Creative Commons Licence.  Visit our mirror at www.physicsweb.altervista.org

 

 

 

Measuring Voltage & Current

 

 

 

Objectives:

 

  
 

 

A multimeter.

  

 

• Know that current is measured using an ammeter, which is connected in series.

 

 

• Know that voltage is measured using a voltmeter, which is connected in parallel.

 

 

• Be able to measure voltage and current in simple circuits.

 

 

  

 

 

 

 

 

 

 

Task 1 - Starter

 

  
 

 

 

 

Think hard!

 

  

 

Find someone who knows:

 

 

1) What voltage means.

 

2) What current means.

 

3) What resistance means.

 

4) How increasing the voltage would affect the current flowing in a circuit.

 

5) How increasing the resistance would affect the current flowing in a circuit.

 

 

 

Your teacher will ask you to share your ideas with the class, and may write some of your ideas, suggestions, and comments on the board.

 

  

 

 

 

 

 

 

 

 

Task 2 - Connecting ammeters and voltmeters

 

  
 

 

Hands up!

 

 

  

 

Your teacher will show you how to connect an ammeter and a voltmeter, to measure the voltage across a component and the current flowing in a circuit.

 

 

 

Watch carefully - you will be building your own circuits next!

 

  

 

 

 

 

 

 

 

 

Task 3 - Building circuits, measuring voltage & current

 

  
 

 

 

A simple circuit.

 

 

  

 

Collect three cells, two bulbs, two 10Ω resistors, an ammeter, a voltmeter, 3 short leads and 5 long leads.

 

 

 

• Build the circuits.

 

• Draw the circuit diagrams.

 

• Measure the current at each of the points specified.

 

• Measure the voltage across the components specified.

 

 

  

 

 

 

 

Build each of these:

 

  
   

 

 

1) One cell connected to one bulb.

    Measure the current in the circuit.

 

2) Two cells connected to one bulb.

    Measure the current in the circuit.

 

3) Two cells connected to two bulbs.

    Measure the current at 3 different points in the circuit.

 

4) Two cells connected to one bulb.

    Measure the voltage across the cells and across the bulb.

 

5) Two cells connected to one bulb and a 10 Ohm resistor.

    Measure the voltage across cells, bulb and resistor.

 

6) Three cells connected to two 10Ω resistors.

    Measure the voltage across the cells, and across each resistor.

  

 

 

 

 

Building circuits worksheet

 

  
 

 

 

A simple circuit.

 

 

  

 

There is a worksheet for this task here:

 

 

Click here to download the worksheet for this task.

 

  

 

 

 

 

 

 

 

Task 4 - Concluding

 

  
 

 

 

 

 

 

  

 

Think about your results from the last experiment...

 

 

 

• What do you notice about the current in all parts of the circuit?

 

 

• How does changing the voltage affect the current?

 

 

• How does changing the resistance affect the current?

 

 

• Is there a connection between the total voltage from the cells and the voltage used by the components?

 

  

 

 

 

 

 

 

 

Task 5 - Thinking about resistance (demonstration)

 

  
 

 

Discuss!

  

 

Think about:

 

 

 

• Are the leads/wires conductors or insulators?

 

 

• Do the wires have any resistance?

 

 

• Will they use any of the voltage?

 

 

 

 

Your teacher will show you a demonstration to illustrate these ideas.

 

 

 

Teacher note:

Use a voltmeter to look at whether voltage is used by the wires/leads; explain ideas of conductivity / resistivity of wires. Model this using the circuit construction kit - wire resistivity can be changed using the slider in the advanced options.

  

 

 

 

 

Explaining ideas - Circuit Construction Kit simulation

 

  
 

This simulation shows us what is happening inside the circuit.

 

  

 

 

Click the image to load the simulation.

 

 

Thanks to PhET for this awesome simulation :)

 

 

 

Java technology!