grade 9 electricty, resistance, power and energy

Electrical Circuits G9

K Warne

V

V1 V2

V1 = 1.5 V V2 = 1.5 V

Vsupply= 3 v

1.5 + 1.5 = 3

V1 + V2 = Vcircuit = Vcell

V

R1 R2

VC = 3 V

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SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY

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Electrical cells

1.5V

One cell Battery (more than one cell)

3 cells connected in SERIES - (+)

side connected to (-) of next cell –

GIVES HIGHER VOLTAGE

+ -

Battery – cells connected in

parallel – (+) to (+) – SAME

VOLTAGE LASTS LONGER

4.5V

(1.5+1.5+1.5)

1.5V

http://www.sciencecafe.org.za/







Measuring Current

The Ammeter: • is connected in ………………… in the circuit (the current

flows through it) • has a …………………… resistance • Is connected positive to ……………. - negative to ……………..

Circuit Symbol:

An ………………. measures the ………….. flowing through the circuit.

+

_ Ammeter

…. 0.0001

The current is the ……………… of ……………….. passing a point in one ………………………. The symbol for current is “…” the unit is ……. (…).










Measuring Current. When measuring the current through a ……………….,

the ammeter is always ………………………….. with

that component (in the …………………… as it).

A










Measuring Potential

The Voltmeter:

• is connected in ……………..to another component in the circuit (the current does NOT flow through it)

• has a …………………resistance • Is connected positive to …………………- negative to

…………………………….

A Voltmeter measures the POTENTIAL (…………..) of the current flowing through the circuit.

+ _

Voltmeter

V 1.50

Resistor

V










Measuring Voltage.

When measuring the voltage across a component, the voltmeter is always

connected in parallel with (or across) the component.

We measure the voltage using a device called an voltmeter. In a circuit

this is given the symbol

The voltage supplied by the battery is shared between all the

components in a series circuit

This is still

a SERIES

circuit.

V3

V2

V1










A

V

component

here

R

Measuring Voltage - across a resistance or a bulb

Voltage is measured by connecting the voltmeter across

(or in parallel) with the component.

Voltage is measured in volts and the symbol for this is V.

V

Components










1. Set up the circuit as shown above.

2. Connect the voltmeter across the power supply and measure the supply

voltage.

3. Then connect the voltmeter across the resistance (R) and measure this voltage.

4. Write down what you have observed:……………………………

……………………………………………………………………….

Experiment: Measuring Voltage

R

V

V

Circuit 1

Voltage cell:………..

Voltage circuit:…………………..










Vsupply = Vcircuit

The supply voltage is equal to the voltage drop across the whole circuit.

NO ELECTRIC POTENTIAL IS LOST IN THE CONDUCTING WIRE.

Experiment: Circuit & cell Voltage

R

V

V

Circuit 1

Voltage cell: Vsupply

Voltage circuit: Vcircuit

Voltage circuit: = Voltage of supply

Vsupply = Vcircuit










1. Set up the circuit as shown above in circuit 1.

2. Measure the voltage of the cell and circiut and current as shown.

3. Now close the switch as in circiut 2. Repeat your measurements.

4. Write down what you have observed:……………………………

……………………………………………………………………….

Open & Closed Circuit

R

V

V

Circuit 1 Voltage

cell:

Voltage circuit

R

V

V

Circuit 1 Voltage

cell:

Voltage circuit

A A










Open & Closed Circuit

R

V

V

Circuit 1 Voltage

cell:

Voltage circuit

R

V

V

Circuit 1 Voltage

cell:

Voltage circuit

A A

Results

Circuit 1: OPEN CIRCUIT Circuit 2: CLOSED CIRCUIT

Supply Voltage

Voltage R1

Current

Supply Voltage

Voltage R1

Current










V1

V2

V3

Voltmeter Voltage

(V)

V1

V2

V3

Experiment: Voltages in parallel

1. Set up the circuit as shown.

2. Measure all the voltages and record them

in the table.

3. Write down what you have

observed:………………………………….

………………………………………………

………………………………………………










Circuit2

R1

V

V1 V2

Circuit2

R2

Measure the voltages indicated in the diagram and note what you

observe: …………………………………………………………………………

……………………………………………………………………………………

……………………………………………………………………………………

……………………………………………………………………………………

V1:……………… V2:………………

Vsupply: ………………

V1 + V2 = ……………

Experiment: Voltages in series










Experiment: Current in a series circuit

1. Set up the circuit as shown

above in circuit 1.

2. Measure the current using the

ammeter at positions 1 and 2.

3. Note down what you observe:

………………………………………..

………………………………………..

………………………………………..

R1

1

2

A

Circuit 1

A

R1 R2 3

4

5 A

A A

Circuit 2

1. Add another resistor into the

circuit as in circuit 2.

2. Now measure the current

using the ammeter at

positions 3, 4 and 5.

3. Note down what you

observe.

……………………………………..

………………………………………

……………………………………..

……………………………………..













X X

X

A1 A2








WIRE

THICKNES

S LENGTHS

CURRENT

(mA)

BRIGHTNESS

NICHROME 0.2 1 180 BRIGHT

2 140 DIMMER

3 120 NO LIGHT

4 100 NO LIGHT

0.4 1 200 BRIGHT

2 180 DIM

3 180 DIM

4 180 NO LIGHT

Length vs Resistance










Energy in Circuits

This section deals with the energy transfers in electric

circuits.

The most important thing to understand about energy is

that it cannot be created or destroyed.

In all devices and machines, energy is transferred from

one type to another.










lamps

When this circuit is connected, chemical energy

stored in the battery is transferred via electrical

energy to heat and light energy in the bulbs.

The total amount of heat and light energy is the

same as the amount chemical energy lost from

the battery.

Energy Transfer in Electrical Circuits










Energy Efficiency

We can work out the efficiency of an energy

transfer:

%Efficiency = x 100

For the bulb

efficiency =......................................

.............. energy input

..............energy output













Hi -

This is a SAMPLE presentation only.

My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as

other resources, are freely available on my resource sharing website:

www.sciencecafe.org.za

(paste into your browser if link above does not work)

Have a look and enjoy!

Keith Warne










grade 9 electricty, resistance, power and energy

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