# Suggested practical - Circuit components

There are different ways to investigate the relationship between and for different circuit elements. In this practical activity, it is important to:

• use appropriate apparatus and methods to measure current and potential difference
• measure and record current and potential difference for a , filament bulb and

## Resistor and filament bulb

### Aims

To investigate the relationship between current and potential difference for a resistor and a filament bulb.

### Method

1. connect the circuit as shown in the diagram
2. ensure that the power supply is set to zero at the start
3. record the reading on the and
4. use the to alter the potential difference
6. repeat steps 3 to 5, increasing the potential difference slightly each time
7. repeat steps 1 to 6, but with the power supply reversed
8. repeat the experiment, but replace the with a bulb

### Results

Record the results in a suitable table. This one shows some example results for a 10 fixed resistor.

Potential difference (V)Current (A)
0.50.05
1.00.10
1.50.15
2.00.20

### Analysis

Plot a graph of current against potential difference for each .

An I-V graph for a fixed resistor at a constant temperatureAn I-V graph for a filament bulb

### Evaluation

For a fixed resistor, the potential difference is directly proportional to the current, so doubling the amount of energy into the resistor results in a current twice as fast through the resistor.

This relationship is called and is true because the of the resistor is fixed and does not change. A resistor is an .

In a filament bulb, the current does not increase as fast as the potential difference. Doubling the amount of energy does not cause a current twice as fast. The more energy that is put into the bulb, the harder it is for the current to flow - the resistance of the bulb increases. As the potential difference increases, so does the temperature of the thin wire inside the bulb, the filament. This increases the resistance of the filament.

## Semiconductor diode

### Aims

To investigate the relationship between current and potential difference for a diode.

### Method

1. Connect the circuit as shown in the diagram. The diode must be protected with a suitable protective resistor (between 100 and 500 ).
2. Set the variable resistor to give the lowest potential difference. Record the readings on the voltmeter and milliammeter (an ammeter capable of reading to ±1 mA).
3. Alter the variable resistor to increase the potential difference by 0.2 V.
5. Repeat steps 3 and 4, increasing the current slightly each time.
6. Reverse the power supply connections and repeat steps 2 to 6.

### Results

Record the results in a suitable table. This one shows some example results.

Potential difference (V)Current (A)
0.20
0.40
0.60
0.80
1.00
1.20
1.41
1.63
1.88
2.020

## Analysis

Plot a graph of current against potential difference.

An I-V graph for a diode

### Evaluation

A diode only allows current to flow in one direction. In one direction, the diode's resistance is very large and no current will flow. In the other direction, the diode's resistance is smaller and current will flow. In this direction, the diode's resistance is very large at low potential differences. At higher potential differences, the resistance quickly drops and current begins to flow.

### Hazards and control measures

HazardConsequenceControl measures
Heating of the resistance wireBurns to the skinDo not touch the resistance wire whilse the circuit is connected, and allow time to cool