202/2 – Know the principles of

basic electrical circuits

Outcome 2.3 – Calculate power

in a basic electrical circuit

Unit 202 Principles of electrical

science

2.2 Apply Ohm’s law to electrical

circuits

Series, parallel.

Last session

2.3 Calculate power in a basic

electrical circuits

Series, parallel.

This session

Power measured in watts

A watt is an amount of work

done in a certain time. One

watt is equal to one Joule per

second.

Power measured in watts

When current flows through a resistor there is a voltage drop.

Due to friction between electrons, electrical energy is converted into

heat or light or both.

Write down three examples of this?

Power measured in watts

Kettle

toaster

Wall heater

GLS Light bulb (tungsten or halogen)

Soldering iron

Hair straighteners

Electric patio heater

Immersion heater

Power measured in watts

It is said that power is

dissipated from a resistor.

Or a resistor dissipates power.

Power measured in watts

Two electrical factors affect power?

__________ __________

Put these values in a formula.

Power measured in watts

Power Voltage

Power measured in watts

Power Voltage

Lets look at V

V=IxR

So….P

I V

V

I R

Power measured in watts

Power Voltage(I x I) = I²

SO

P=I²RP

I I x R

V

I x R

Power measured in watts

Power Voltage

Lets look at I

I=VR

So….P

I V

V

I R

Power measured in watts

Power Voltage(V x V) = V²

SO

P=V²R

P

VV

RIV

R

Choose the appropriate formula and calculate the power dissipated in each resistor?

230volts

Calculate the total power dissipated in the series circuit?

Calculate power

10Ω5Ω 20Ω

Calculate the total power dissipated

230volts

Calculate the power dissipated in each resistor.

Calculate power

5Ω

7Ω

13Ω

Current and power

Current decreases, power _________

Current increases, power _________

Voltage and power

Voltage decreases, power _________

Voltage increases, power _________

Voltage and power

In Barbados, supply voltage is 115V

How long would a UK kettle take to boil?

Voltage and power

Discuss in groups

What would be the difference in a UK

and Barbados kettle which both took

the same time to boil?

Kettles

UK Barbados

20Ω 10Ω

230v 115v

Calculate power dissipated in both countries

How does resistance

affect power dissipated?

How does resistance

affect power dissipated?

20Ω 10Ω

230v 230v

Calculate power dissipated in both circuits

Draw 5 resistors (1 to 100Ω) in a series/parallel configuration.

Give it a supply voltage.

Swap with a friend.

Calculate the total power dissipated.

Individual task

Consolidation

Power triangles

Formula transposed

How does voltage affect power dissipated?

How does resistance affect power dissipated?

2.3 Calculate power in a basic

electrical circuits

Series, parallel.

Consolidation

2.4 State how instruments are

connected into circuits in order to

measure electrical quantities.

Voltmeter, ammeter, wattmeter,

ohmmeter.

Next session