Electric Current

Remember: Copper atoms are much bigger than electrons and are packed together in the wire.

+

April 19, 2023

In an electric c____, current is the flow of e_______. The bigger the current, the m___ electrons are flowing around the circuit. The w___ carry the electrons from one terminal

around the circuit to the other t______.

Current

lamps

ircuitlectrons ore

ireserminal

5.2 Resistance

• Resistance is measured using an ammeter and a voltmeter.

• Resistance = Voltage Current• This is called Ohm’s Law• Resistance is measured in Ohm’s

(Ω)

April 19, 2023

ΩOmega

How many different words can you spell from the word resistance?

Measuring Current

A

AA

Current is measured using an ammeter connected in series.

What will the 3 ammeters read in this circuit?

1

2

3

Ammeter 1 = 0.15A, Ammeter 2 = ____, Ammeter 3 = ____

Measuring Current

A

AA

Current is measured using an ammeter connected in series.

What will the 3 ammeters read in this circuit?

1

2

3

Ammeter 1 = 0.15A, Ammeter 2 = 0.15A, Ammeter 3 = 0.15A

In a series circuit the current is always the same.

Current in parallel

A1

A2

A3

A4

In a parallel circuit the current can split depending on how difficult each route is.

The total current into and out of the supply is always the same.

What are the missing currents?

A1 = 0.6A

A2 = _____?

A3 = 0.2A

A4 = _____?

April 19, 2023

Current in parallel

A1

A2

A3

A4

In a parallel circuit the current can split depending on how difficult each route is.

The total current into and out of the supply is always the same.

What are the missing currents?

A1 = 0.6A

A2 = 0.4A (A1-A3 = 0.6A-0.2A)

A3 = 0.2A

A4 = 0.6A (A1 = A4)

Measuring Voltage

V2 V3

V1

NB Voltmeters are connected in parallel

Voltmeter Voltage

(V)

V1 1.5

V2 0.6

V3 0.9

Voltage measures how energy changes around the circuit. It compares the energy in one part with another and shows the difference.

In series V1 = V2 +V3

Voltage in Parallel

V1

V2

V3

Voltage only changes when energy changes. In this circuit energy changes happen at the cell and the bulbs.

V1 = V2 = V3

Voltmeter Voltage

(V)

V1 1.5

V2 1.5

V3 1.5

Measuring Resistance

V

A

Resistance = Voltage

Current

Set up the circuit as shown below:

Slowly move the variable resistor and for each setting record the current in amps and the voltage in volts.

Plot a graph of your results.

Voltage

(V)

Current

(A)

Resistance

(Ω)

0

2

4

6

8

12

Graphs

Voltage against current through a resistor

0.00

0.100.20

0.30

0.40

0.500.60

0.70

0.80

0 0.5 1 1.5 2 2.5 3 3.5 4

Voltage (Volts)

Cu

rren

t (A

mp

s)

Suitable labels – Quantity (Units)

Scale uniform

Correct type of graph

Bar chart for categoric data

Line graph for continuous data

Points plotted correctly

ISA Answers

1. I was trying to find out if the current flowing through a resistor depends on the voltage across it.

2. Independent variable = Voltage

Dependent variable = Current

3. Voltmeter or Ammeter

4. The smallest scale division was 0.01V or 0.01A

5. Smaller scale division means more precise measurements

6. Use the same resistor

Different resistance values change the current

8. As the Voltage increases the current increases

Section 2

10.As temperature increases the resistance falls

11.Range 0º C to 150ºC

No. 150ºC too high for room temperatures.

12.At these temperatures resistance only changes very slightly.

13.50ºC circled.

Not anomalous. More likely to be 25ºC

14.Thermistor tested might not be typical

between 50 and 200 (5 to 20%)

15.Results would be more reliable

16.Have smaller intervals between readings

17.Company was changing the results.Avoiding bad publicity.Would damage the companies reputation.

18. Improves the reliability19.They have had a scale marked on them

A range either side of the expected value that is considered acceptable5%

Testing the effect of current on a wire

A Test Wire

Voltage (V)

Current (A)

Resistance (Ohms)

2

4

6

8

12

Circuit Results

5.2 Resistance

• Resistance is measured using an ammeter and a voltmeter.

• Resistance = Voltage Current• This is called Ohm’s Law• Resistance is measured in Ohm’s

(Ω)

April 19, 2023

ΩOmega

How many different words can you spell from the word resistance?

Resistance of a wire (ISA)• To investigate which factors

change the resistance of a wire.

April 19, 2023

Apparatus: Resistance wire, Voltmeter, Ammeter, Power supply, Leads, Crocodile clips, metre ruler, Variable resistor.

V

A Test Wire