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KS3 Current Topic BookletElectrical Current

Big Picture

Current is a flow of electricity which results from electrically charged particles all moving in one direction. Is most cases, the electrically charged particles are negative electrons (as in electrons from the atom). The word current comes from the Latin word “currere” which means to run or flow. The electron can be imagined to be running around the circuit like the current of a river is the flowing.

Some facts about current: An electric current is a flow of negatively charged electrons. A circuit is a complete path along which current can flow. If a circuit is not complete, current will not flow. Cells and batteries give the electrons energy to flow around the circuit. Voltage is the amount of energy given to the electrons. High voltage – more energy is given

to the electrons.

A model for electricity involves water flowing around a closed pipe, see blow.

KS3 Current Topic Booklet 1

In this model, the water flows around the pipes and we can compare the water to electrons and the pipes to a circuit. So we can say the electrons flow around the circuit. The pump is pushing the water around the pipes, in the same way the battery (or cell) is pushing he electrons round the circuit. Also, the turbine is using some of the water’s energy, which is the same as the bulb is using some of the electron’s energy.

1. What is current?Current is a flow of negatively charged electrons

2. What is a circuit?A circuit is a complete path along which a current can flow

3. How does current flow?Cells and batteries give electrons energy to flow around the circuit

4. How is a pump like a battery?The pump pushes the water around the circuit like the cell/battery pushes electrons round a circuit

5. How is a pipe like a circuit?The pipes carry the water around like the circuit and wires carry the electrons around

6. How is a turbine like a bulb?A turbine is like a bulb as it transfers the energy of the flowing water into movement like a bulb transfers the electrical energy of the cell into light

7. What would happen if there was a hole in the pipe? Would the water still flow?If there was a hole in the pipe the water would leak out of the pipe, the water would still flow but not as quickly.

For the current to flow around the circuit it be complete and there must be a battery. Like in the model above, the water will not flow around the pipes if there is a hole in the pipe or no pump. When we draw circuits, we can use a line to represent the wire between the parts of the circuit such as the bulb and the battery. See the diagram below showing the complete and incomplete circuits.

KS3 Current Topic Booklet 2

Look at the circuits above. The first one is incomplete as there is a break in the wire next to the bulb. The second has no battery and therefore the electrons aren’t being pushed around. The third is a complete circuit and the bulb lights up.

Look at the diagrams on the next page and answer the questions underneath.

8. Will the bulb in circuit 1 light up? Why?Yes, the circuit is complete

9. Will the bulb in circuit 2 light up? Why? No, both the wires are connected to the same side of the cell so the electrons can’t flow

10. Will the bulb in circuit 3 light up? Why?No, there is a gap in the circuit between the bulbs so the electrons can’t flow

11. Will the bulb in circuit 4 light up? Why?Yes, all the components are connected correctly, with no gaps.

Drawing all the batteries out and bulbs out can take a long time, so physicists developed symbols to use to represent all the frequently used equipment. These are shown below

KS3 Current Topic Booklet 3

You need to learn and know these symbols as it help you answer questions all the way to A-Level physics!

Study the table, then cover and complete the table below.

Symbol Name Purpose 12 Cell Produces current

13 Voltmeter Measures the voltage or the difference in energy at 2 points in the circuit

14 Bulb or lamp Thin wire that heats up when current flows through it to transfer electrical energy into light

15 Battery A group of cells

KS3 Current Topic Booklet 4

16 Open Switch Causes a break in the circuit, stops current flowing.

17 Resistor Limits the flow of current through a circuit

18 Ammeter Measure amps or the flow of electrons per second

19 Closed switch A closed switch completes the circuit and allows current to flow

20. Draw a circuit below containing a bulb, cell and open switch. Will current flow around your circuit? Why?

No current will not flow as there is a gap in the circuit so the circuit is not complete

21. Draw a circuit below containing a bulb, cell and closed switch. Will current flow around your circuit? Why?

KS3 Current Topic Booklet 5

Yes, current will flow because the circuit is complete

22. Draw a circuit below containing a bulb, battery and open switch. Will current flow around your circuit? Why?

No current will not flow as there is a gap in the circuit so the circuit is not complete

23. Draw a circuit below containing a bulb, cell, resistor and closed switch. Will current flow around your circuit? Why

KS3 Current Topic Booklet 6

Yes, current will flow because the circuit is complete

Complete the sentences:24. In a complete circuit containing a battery and a bulb, the bulb lights up because there are no

gaps so the electrons can carry the charge around the circuit

25. In a complete circuit containing a battery and a bulb, the bulb lights up but the circuit needs to have no gaps.

Series and parallel circuits

Circuits can be set up in two ways, series and parallel. The way a circuit is set up has a big effect of the current or flow of electrons, which is measured in amps using an ammeter.

26. What is the symbol for an ammeter?

KS3 Current Topic Booklet 7

Series Parallel

The diagrams above show two circuits, the left is in series and the right is parallel. Both circuits contain a battery and 2 bulbs but are arranged differently.

The word series means to line up or put in order and is a Latin word. In a series circuit, all the bulbs are lined up, one after the other, and the current flows through each in turn.

The word parallel comes from the Greek parallelos and means side by side. The bulbs are not lined up, they are placed side by side and the current has to be shared between them.

When measuring current we use an ammeter, like the ones seen in this diagram (to the right). The ammeters measure the flow of electron (current) and therefore, they have to be in the circuit for the current to flow through them

In a series circuit, the current flows around the circuit and doesn’t need to be shared between parallel wires. This means that the current at any point in a series circuit is equal and the same. The diagram to the left is showing this.

27. What is an ammeter? A device used for measuring the current in the circuit

28. What does it measure and what units does it use?It measures current and the units used are Amperes or more commonly Amps (A)

29. When there is a break on the circuit what is the reading?0A

30. What is the connection between the reading and the brightness of the bulb?The higher the reading on the ammeter and therefore the higher the current the brighter the bulb

31. What happens to the current at different places in a series circuit?Current is the same everywhere in a series circuit

32. Complete the values in the circuit below

KS3 Current Topic Booklet 8

In a parallel circuit, this is not the case. The ammeters are still in the circuit but the bulb and ammeters are placed in parallel (side by side) wires. This means the current has to be split fairly between the parallel wires and so it is split in 2, assuming there are only 2 parallel wires.

For example, if 0.2 A is needed to light up each bulb, then 2 x 0.2 A must leave the battery. The current splits in two at the parallel part, and then joins up again (see diagram below).

33. Complete the values in the circuit below

KS3 Current Topic Booklet 9

0.5

0.2

0.5

0.2

0.2

34. Complete the values in the circuit below

35. Complete the values in the circuit below

36. What does it measure and what units does it use?IGNORE

37. When there is a break on the circuit what is the reading?IGNORE

38. What happens to the current at different places in a parallel circuit?

KS3 Current Topic Booklet 10

0.2 0.2

0.15

0.15

0.75 0.75

0.1

0.1

0.3 0.3

0.25

0.25

0.25

0.25

0.5

Current in a parallel circuit splits up down the branches of the circuit and then re-joins.

Summary Questions

39. Name the two types of circuitsSeries and Parallel

40. What is this and what does it do?Ammeter and measures the current in a circuit

41. What is an insulator? Name 2 materials that are insulatorsA material that does not conduct electricity e.g. plastic wood, rubber, polystyrene, air

42. Label the current through the other two ammeters

43. Label the current through the other two ammeters

KS3 Current Topic Booklet 11

3.7A 3.7A

2.5A

5.0A

44. Draw a series circuit with two bulbs, a switch and two cells.

45. Draw a parallel circuit with two bulbs, a switch and two cells The switch must turn the both bulbs on when closed

KS3 Current Topic Booklet 12