Prac 1 - Length and Resistance of a wire

What is the aim?

To investigate the relationship between current and thickness of a wire.

What is the hypothesis?

As the length of the wire increases, the resistance of the wire increases.

This is because…

• There is an increasing number of metal ions so the chance of more collisions between the eletrons and metal ions increase.

• These collisions will slow the current flow, increasing the resistance.

What are the variables?

Independent variable = Thickness of the wire/number of wires.

Dependent variables = Current (A), Voltage (V)

Control variables = Components, e.g. Battery (1.5v)

• Wire used

• Temperature in room

What are the Risks, Precautions & Emergency Procedures of the Hot wires? (H&S)

Hazard: Hot wires

Risks: Burns

Precaution:

• Use tongs or similar to move recently used wires.

• wear goggles/lab coat,

• Leave the equipment for a few minutes to cool down before preparing the next set.

Emergency Procedures: Run the burnt area under cold water for 20 minutes/ Contact first aid.

What are the Risks, Precautions & Emergency Procedures of Electric Current? (H&S)

Hazard: Electric current

Risk:

• Electric shock

• Risk of toxic and corrosive chemicals if batteries are used.

Precautions:

• Use the lowest voltage possible

• Avoid water or liquids coming into contact with the circuit.

• Avoid overloading circuits.

Emergency Procedures:

• Break contact by switching off the circuit or plug

• Use a wooden item such as a broom handle to pull the casualty clear.

• Contact first aid immediately.

What are the Risks, Precautions & Emergency Procedures of Sockets? (H&S)

Hazard: Sockets

Risks: Electric shock

Precaution:

• Avoid water or liquids coming into contact with the sockets/plugs

• Check that the plugs are correctly wired and that primary & secondary insulation is in good condition.

Emergency procedures:

• Break contact by switching off the circuit or plug

• Use a wooden item such as a broom handle to pull the casualty clear.

• Contact first aid immediately.

What are the Risks, Precautions & Emergency Procedures of Resistance Wires (H&S)

Hazard: Resistance wire

Risks: Cuts/piercing skin

Precautions:

• Wear gloves/goggles/lab coat

• Handle with care

• Avoid touching the ends of the wire

Emergency Procedure: Any cuts, apply pressure and contact first aid.

What are the Risks, Precautions & Emergency Procedures of Metere Rule (H&S)

Hazard: Metere Rule

Risks: Splinters

Precautions: Avoid running hands along rule, especially any exposed splinter areas

Emergency Procedures:

• Any splinters that can be removed should be

• Deep splinters - seek first aid.

What was the equipment used?

Switch: Turns on and off the current

1.5v cell: to push the electrons around the circuit.

Ammeter (digital): to measure the current (Amps)

Length of wire attached to the metre rule: to show the exact length of the wire

Crocodile clip: to keep the wire attached to metre rule

Jockey: as a movable contact or small flathered screwdriver and additional crocodile clip connecting leads.

Voltmeter (digital): to measure the potential difference (voltages)

What was the method?

1) Using equipment provided, set up the circuit shown below.

2) Close the switch. Place the movable contact on the wire so that the length L is 10cm.

3) Measure and record the potential difference V and the current I.

4) Repeat the steps above and change the value of L, increasing 10cm each time.

5) Work out the resistance R using the equation R = V / I

6) Plot a graph of R (y-axis) against L (x-axis) and draw the best straight line through the points

7) Determine the gradient of the line.

What was the conclusion?

In conclusion, the results show that the length of the wire is directly proportional to resistance (ohms)

This is shown: use two points of the graph

e.g. at 20cm the resistance was at 2.59 (ohms) and by 40cm the resistance basically doubled at 5.04 (ohms).

As the length of the wire increases, the metal ions increase,d leading to more collisons between the metal ions and electrons.

This will increase the resistance as the collisions slow the current flow.

Furthermore, there are also systematic errors in the equipment:

• The wire may have been bent

• The temperature was not controlled.