Lesson 4: Measuring Circuits

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Why do we need to measure?

Knowing how to measure electricity may seem useful, but why? 

With your table, discuss why measurement may be useful?

New Information

Measuring Electricity

When we measure electricity you don’t often hear people referring to Ohm’s or volts or amps. 

• This is because no one unit can summarise the information need. 

Watts 

• This is the standard unit of power, most devices are measured in it. 

• 1 Watt uses 1 Joule of energy per second. 

• You can calculate Watts using the formula: Watt = Ampere x Volt

Why should we measure electricity?

1. Due to differences in resistance of materials some substances cannot handle lots of current or voltage 

   • We need to limit the amount of watts on devices to prevent electrical fires and destroying devices.

2. Sometimes our devices lose their voltage over time, it is useful to ensure they are operating at optimal capacity. 

3. Sometimes we experience voltage drop 

   • Voltage drop is the reduction in the voltage of a circuit. 

     • As a result of passing through difference devices or the length of a cable. It is dependent on the resistance of the device.

In the figure on the top right, you can see a computer has a 19-volt limit but the voltage from the power point is 240 (over ten times) so we use a transformer to reduce the voltage.

In the figure on the bottom right, due to the length of the wire the voltage is reduced.
You can think of this like blowing in a straw the longer the straw the harder it is to maintain the pressure.

How do we meaure electricity?

We use 3 main devices to measure a circuit 

1. An ammeter 

   • Measures current 

2. A voltmeter 

   • Measures voltage 

3. A multimeter 

   • Measures multiple units at once.