Electricity 2 Thomas Edison 1847-1931. Lesson Objectives I know some circuit symbols for common components. I know what is meant by resistance I know.

Thomas Edison 1847-1931

Task:

Draw some circuit symbols for common components found in an electrical circuit.

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Cell – push electrons around the circuit

Battery – consists of 2 or more cells Switch – enables

current to be switched on or off

Lamp – emits light

Ammeter – measures current.A

Voltmeter – measures voltageV

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The ones you should know already

Other Components and their symbols:

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Diode – only allows current in ONE DIRECTION ONLY.

Fixed resistor – limits current flowing in a circuit

Variable resistor – varies current flowing in a circuit

Other Components and their symbols:

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Fuse – a wire that melt when current is TOO high.

Heater – converts electrical energy into thermal.

Circuit 1 Circuit 2 Circuit 3

1 cell, 1 bulb 1 cell, 2 bulbs 1 cell, 3 bulbs

A1 A1 A1

A2 A2 A2

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Conclusion – current is the same in all places in a SERIES circuit.

N

N = normal brightness B = bright D = dim

Circuit 1 Circuit 2 Circuit 3

Circuit 5Circuit 4 Circuit 6

1 cell 1 bulb 2 cells 2 bulbs 3 cells 3 bulbs

3 cells 1 bulb1 cell 2 bulbs2 cells 1 bulb

N N N N N

B BD D

Conclusion – voltage is the shared between

components in a SERIES circuit.

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Voltage in a series circuit

The battery provides energy to the circuit. The energy in the battery is stored as chemical energy and is transformed into electrical energy. This energy is carried by the electrons around the circuit.

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Potential Difference (PD)

Potential Difference (PD) is a measure of the energy flowing through a part of the circuit and is measured in Volts (V) using a voltmeter

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Potential Difference (PD) in a series circuit.

A voltmeter is places in parallel to measure the Potential Difference (PD) across a component.

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?V

3V

3V

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3V

1.5V1.5V

All of the bulbs are now dimmer as the Potential Difference (PD) is shared between the two bulbs

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3V

1V1V1V

All of the bulbs are now dimmer as the Potential Difference (PD) is shared between the three bulbs

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Conclusion:

Current is the same at all points in a series circuit.

Potential Difference (PD) is shared between the components in a series circuit.

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Resistance:

When electrons pass through a component, they will experience a different amount of resistance.

This is caused by the vibrating atoms getting in the way of the electrons trying to get through.

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Resistance:

This is measured by:

Potential difference (volts) = Resistance (Ohms) Current (amps)

Short hand:

R = V I

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The current through a wire is 2.0A when the potential

difference across it is 12V. Calculate the resistance of the

wire. 12/2 = 6 Ohms ()

Resistance:

When current passes through a wire it gets hot. These are results from a set of students who investigated if resistance changes when current is changed.

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Current (A) 0.05 0.10 0.15 0.20 0.25

Potential difference (V)

0.50 1.00 1.50 2.00 2.50

Draw a graph of results and write a conclusion.

Conclusion:

Current is directly proportional to potential difference in this wire.

Therefore, resistance remains constant.

This is known as Ohm’s law – “The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor”. (Known as an Ohmic conductor).

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A filament lamp

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• Curve – therefore not directly proportional, so not an ohmic resistor.

• Resistance increases as current increases

• Caused by increase in temperature as current increases.

• Reversing the current has not effect – they are a mirror image.

Diode

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• Only works in ONE direction

• No a straight line – so not an ohmic conductor.

• Reverse direction, the current is negliable.

Thermistor

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High Temp

Low Temp

Cur

rent

Potential Difference

• Straight line – therefore directly proportional, so an ohmic resistor at constant temperature.

• Resistance decreases as temperature increases

Light dependent resistor (LDR)

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High Light

Dim light

Cur

rent

Potential Difference

• Straight line – therefore directly proportional, so an ohmic resistor at constant temperature.

• Resistance decreases as light increases

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.