Measuring Current

Learning Objectives:

• Describe current as a flow of electrons.

• Link amount of cells in a circuit to the size of the current.

Measuring electric currentWe can measure the amount of electric current flowing through a circuit using a device called an “ammeter”.

Current is measured in Amperes.

A

What is the trend here?

2 electrons per second = 1A

8 electrons per second = 4A

4 electrons per second = 2A

12 electrons per second = 6A

Rich questions:

• Which way do electrons flow?

• Do electrons always flow the same way around a circuit?

Measuring Current

• How much the current is flowing is the number of electrons passing a point every second.

• Therefore current depends on how many electrons are moving and how fast they are moving.

• Current & Voltage in a circuit

The unit of measure for current is the amp, which has the symbol A.

A

Measuring current

AA

Current is measured using a device called an ammeter. In a circuit diagram, an ammeter is shown by the symbol .

When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component.

1

2

1. Set up the circuit as shown above.

R1

A

A

Experiment 1: Current in series circuitCircuit 1

2. Measure the current using the ammeter at positions 1 and 2.

3

1. Add another lamp into the circuit (R2) and another ammeter after it.

R1

A

A

A

R2

Experiment 1: Current in a series circuitCircuit 2

1

2

2. Now measure the current using the ammeter at positions 1, 2 and 3.

Circuit 2 results:

Current at position 1 =

Current at position 2 =

Current at position 3 =

Circuit 1 results:

Current at position 1 =

Current at position 2 =

Experiment 1: Current in a series circuit – results

R1A

A

Circuit 1 Circuit 2

R1 R2A

AA1

2

1

2

3

Draw each circuit and trace the path of the electrons through the circuit

Experiment 1: Current in a series circuit – summary

Circuit 1The current at different positions in the circuit, before and after the lamps, was the _______.

Current is _____ used up by the components in the circuit.

Circuit 2Increasing the number of components in the circuit ________ the current.

The current at all points in a series circuit is the _______.

same / same / decreased / not

Circuit 1 Circuit 2

R1A

A R1 R2A

AA

Current in a series circuit

If the current here is 2 amps…

The current here will be…

The current here will be…

And the current here will be…

In other words, the current in a series circuit is THE SAME at any

point

Compare and contrast

• Do not attempt to answer the question initially• Discuss with neighbour which of two questions

do you think is highest level and why?Level• Current is a flow of electrons• Would there be more or less electrons flowing if

the current was large?Level • Current is a flow of electrons• Which of the three currents (2A, 5A or 10A)

would have the largest flow of electrons?

Next lesson

• What do you think we should be learning next lesson?

Measuring Current

Learning Objectives:

• Describe current as a flow of electrons.

• Link amount of cells in a circuit to the size of the current.