Prescribed GCSE Physics Practicals

Question 1

How can you investigate and obtain readings on the relationship between current and voltage?

How can you prove Ohm’s Law? Draw a circuit diagram for doing so.

Question 2

What is the experimental method for investigating the Current through and the Voltage across a Metal Wire at a Constant Temperature?

Answer 2

1. Prepare a results table. Current, voltage, and resistance heading each column.
2. Adjust the Power Supply Unit (PSU) dial to 0 V and make sure it is switched off.
3. Set up the circuit as shown on the diagram.
4. Switch on the PSU and in a table of results record the voltage across the wire and the current flowing through it.
5. Switch the PSU off immediately after taking the results and allow about 30 seconds for the wire to cool down - this makes sure that it stays at a constant temperature and doesn’t overheat.
6. Turn the PSU on again and adjust it until there is a reading of 0.20 A on the ammeter. Again take the corresponding value for voltage, turn the PSU off and allow a short time for the wire to cool again.
7. Repeat step 6 for current values of 0.40 A, 0.50 A, 0.60 A, 0.80 A,

Question 3

What is the conclusion to the Current through and voltage across a metal wire investigation?

Answer 3

The graph produced is a straight line through the origin (0,0) so current is directly proportional to voltage.

Table shows V/I = constant value so this also means that current is directly proportional to voltage. Our evidence shows that it obeys Ohm’s Law.

Question 4

How can you investigate the effects of Length on on the resistance of a Metallic Conductor (metal wire)?

Draw a circuit diagram for doing so.

What is the independent, dependant and controlled variable in your investigation?

Answer 4

The independent variable is: the Length of the Wire.

The dependent variable is: the Resistance of the wire (via ammeter + voltmeter readings)

Controlled variables are: the Temperature of the wire, the material of the wire and the thickness of the wire (cross-sectional area).

Question 5

What is the experimental method for investigating the effects of Length on on the resistance of a Metallic Conductor (metal wire)?

Answer 5

1. Prepare a results table as below.
2. Use tape to stick a 1m length of constantan wire to a metre rule, making sure there are no kinks in it, and set up the circuit as drawn. Ensure that the PSU is initially turned off and set at 0V.
3. Connect the moveable leads to 1m of the wire.
4. Turn on the PSU and adjust the current, using the variable resistor, to about 0.60A. Record this current plus the voltage from the voltmeter in the results table. We are keeping the current low so that eire does not overheat.
5. Now reduce the length of wire to 90cm by moving the leads and repeat step 4.
6. Keep reducing the wire by 10cm and repeating step 4 until you reach a length of 10cm.
7. Record all results in the table.
8. Calculate the resistance for each length of wire by dividing the voltage value by the current value.
9. Finally plot a graph of Resistance on the y-axis against Length on the X axis.

Question 6

What is the conclusion to the investigation of the effects of Length on on the resistance of a Metallic Conductor (metal wire)?

Answer 6

The graph produced is a straight line that passes through the origin (0,0).

This tells us that the length of the wire (at a constant temperature) is directly proportional to its resistance.

Explanation:

As the length increases so too does the number of vibrating ions (that the electrons need to move past). Hence there are more collisions occurring between free electrons and the vibrating ions, in other words is a greater opposition to current flow i.e. a greater resistance.