202/2 – Know the principles of

basic electrical circuits

Outcome 2.2 – Apply Ohm’s law

to electrical circuits

Unit 202 Principles of electrical

science

Last session

2.1 Calculate resistance of a conductor in a basic electrical circuit

Copper conductor, aluminium conductor, silver conductor, gold conductor, brass conductor.

2.2 Apply Ohm’s law to electrical

circuits.

Series and parallel.

This session

Draw three resistors in series?

Series resisters

If these three resistors are 5Ω, 10Ω and 20Ω

what would be the total resistance?

Series resistors

RT = R1 + R2 + R3

Series resistors

RT = 5Ω + 10 Ω + 20Ω

= 35 Ω

Series resistors

What if there were 5 resistors

connected in series?

Series resistors

RT = R1 + R2 + R3 + R4 + R5

And so on.

Series resistors

Draw three resistors connected in parallel?

Parallel resistors

If these three resistors are 5Ω, 7Ω and 13Ω

what would be the total resistance?

Parallel resistors

1 1 1 1

RT = R1 + R2 + R3

Parallel resistors

1 1 1 1

RT = 5Ω + 7Ω + 13Ω

1

RT = 0.2 + 0.14 + 0.07

1

RT = 0.41Transpose and solve…….

Parallel resistors

What if there were 5 resistors?

Parallel resistors

What if there were 5 resistors?

1 1 1 1 1 1

RT = R1 + R2+ R3+ R4+ R5

and so on

Parallel resistors

Parallel rule?

Parallel resistors

In parallel, the total

resistance is always less

than the smallest resistor.

Parallel rule

Series resistors connect in a line.

More resistors more resistance.

Parallel resistors connect together at each end.

More resistors less resistance.

Formulae?

Parallel rule?

Resistors in series or parallel

There is only one path for current to flow through

a series circuit.

230volts

Current must be the same throughout the circuit.

Using Ohms law calculate current.

Current in a series circuit

10Ω5Ω 20Ω

100 volts is across all three resistors, this voltage is shared across them.

V1 V2 V3

230volts

If we know the resistance and the current through each resistor we can calculate voltage.

Calculate V1, V2 and V3 then add together

Voltage in a series circuit

10Ω5Ω 20Ω

There are numerous paths for current to flow through in a parallel circuit.

230volts

Current will split through the parallel circuit.

Using Ohm’s law calculate current.

Current in a parallel circuit

5Ω

7Ω

13Ω

The voltage will be the same across all three resistors.

230volts

1. Calculate current through each resistor then add them.

2. Calculate total resistance then total current, compare.

Voltage in a parallel circuit

5Ω

7Ω

13Ω

2.2 Apply Ohm’s law to electrical

circuits

Series, parallel.

Consolidation

2.3 Calculate power in a basic

electrical circuits

Series, parallel.

Next session