Current Electricity – Learning Outcomes

Test electrical conduction in a variety of materials, and classify each material as a conductor or insulator.

Set up a simple electric circuit.

Use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them.

Demonstrate simple series and parallel circuits containing a switch and two bulbs.

Perform simple calculations based on the relationship between current, potential difference (voltage), and resistance.

1

Test Electrical Conduction Recall the definitions of conductors and insulators:

A conductor allows charge to flow through it easily (e.g.

metals).

An insulator does not allow charge to flow through it

easily (e.g. plastic, glass).

To detect if a material is a conductor or an insulator, we

must know if charges can flow through it.

An electric current is a flow of electric charge.

2

Test Electrical Conduction Electrical diagrams use special symbols to mean certain

things:

3

Power Supply

/ Battery

Bulb

Switch Resistor

Test Electrical Conduction1. Set up a circuit with power supply, bulb, switch, and

open connection in series.

2. Place an object in the open connection and check if

the bulb lights.

3. Replace the object with other objects of different

materials and check if the bulb lights.

4

Set Up a Simple Electric Circuit To be a circuit, there must be at least one unbroken

connection between the two ends of the power supply.

All circuits have a power supply, which provides a

certain amount of potential difference / voltage / e.m.f.

which gives energy to the circuit.

The unit for potential difference is volt (V).

A voltmeter is used to measure the potential difference

between / across two points in a circuit.

5

Set up a Simple Electric Circuit An electric current is the flow of electric charges.

The unit for current is the amp (A).

An ammeter is used to measure current through a part

of a circuit.

6

Set up a Simple Electric Circuit Recall that conductors allow current to flow and

insulators do not.

In reality, insulators are just bad conductors – i.e. they

allow some current to flow, but not much.

The amount of current that flows is determined by

resistance.

Good conductors have low resistance and bad

conductors have high resistance.

The unit of resistance is the ohm (Ω).

Resistance can be measured with an ohmmeter.

7

Set up a Simple Electric Circuit Some devices can change their resistance to become

good or bad conductors.

These are called variable resistors or rheostats.

They are used in e.g. dimmer switches, oven

temperature scales, etc.

8

Measure Current Ammeters need to be wired in series with the object you

are measuring the current through.

9

Measure Potential Difference Voltmeters need to be wired in parallel with the object

you are measuring the potential difference across.

10

To Measure Resistance (Expt 30 part a)1. Attach an ohmmeter to both ends of a coil of wire.

2. Note the resistance.

11

To Measure Resistance (Expt 30 part b)1. Set up a coil of wire in series with an ammeter, power

supply and variable resistor (or variable power supply).

2. Wire a voltmeter in parallel with the coil of wire.

3. Measure the potential difference across and current

through the coil.

4. Vary the resistance of the variable resistor to get

additional measurements for potential difference and

current.

5. For each measurement, divide potential difference by

the corresponding current and find an average.

12

To Measure Resistance (Expt 30 part b)6. Plot a graph of potential difference vs current for the

coil of wire and for the bulb.

7. Find the slope of the graph.

13

Demonstrate Series Circuits1. Wire a power supply, switch, and two bulbs in series.

2. Note what happens to the bulbs when the switch is

closed.

3. Disconnect one bulb and note what happens to other

bulb.

14

Demonstrate Series Circuits Advantages:

Uses less electricity than parallel.

Disadvantages:

One faulty component will prevent the whole circuit

from working.

Used in e.g. Christmas lights.

15

Demonstrate Parallel Circuits1. Wire a pair of parallel bulbs in series with a power supply

and a switch.

2. Note what happens to the bulbs when the switch is

closed.

3. Disconnect one bulb and note what happens to the

other bulb.

16

Demonstrate Parallel Circuits Advantages:

If one component fails, the rest of the circuit still works.

Disadvantages:

Uses more power than series.

Used e.g. in car headlights.

17

Solve Problems About Resistance Fill in the blanks in the table below using the resistance

formula 𝑉 = 𝐼𝑅.

18

Potential Difference (V)

Current (I) Resistance (R)

10 5

2 200

120 30

100 2

0.5 20

120 10