GCSE Physics Required Practical: Investigating Electrical Components

Key Stage 4

Meaning

Investigate the I-V characteristics of electrical components.

Experiment 1a: Resistor

Variables

Independent Variable: The potential difference across the resistor.

Dependent Variable: The current through the resistor

Method

Connect an ammeter in series with the resistor to measure current through the resistor. Connect a voltmeter in parallel with the resistor to measure the potential difference across it. Use a variable resistor in series with the resistor to vary the potential difference across the resistor. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the readings on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current.

Improving Precision

Use the same component for each repeat. Do not just use the same value of component as they may be slightly different from one another.

Use a low current and turn the circuit off between readings. This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings.

Results

Description

The IV Graph for a resistor shows that:

• As potential difference increases, increases.
• The relationship between potential difference and current is linear (the gradient is constant).
• The current is directly proportional to potential difference.

Explanation

Resistors obey Ohm's Law so the "current through a resistor at constant temperature is directly proportional to the potential difference across the resistor."

Experiment 1b: Filament Bulb

Variables

Independent Variable: The potential difference across the bulb.

Dependent Variable: The current through the bulb

Method

Connect an ammeter in series with the bulb to measure current through the bulb. Connect a voltmeter in parallel with the bulb to measure the potential difference across it. Use a variable resistor in series with the bulb to vary the potential difference across the bulb. Start with a potential difference of zero and increase the potential difference by an interval of 1V up to 10V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current.

Improving Precision

Use the same component for each repeat. Do not just use the same value of component as they may be slightly different from one another.

Use a low current and turn the circuit off between readings. This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings.

Results

Conclusion

Description

The IV Graph for a bulb shows that:

• As potential difference increases, increases.
• At small potential differences] the the relationship between potential difference and current is linear (the gradient is constant).
• At large potential differences the gradient becomes more shallow as the resistance of the bulb increases.

Explanation

At small potential differences there is a small current so the heating effect of the current is small and the filament remains at a low temperature.

At large potential differences there is a large electrical current so the heating effect of the current is large which causes the filament to be a high temperature.

This is caused by electrons in the wire colliding with ions in the metal lattice causing them to vibrate.

Wires (like the filament) have a greater resistance at higher temperatures, causing the increase in current to be reduced.

This is because the more the ions in the metal lattice vibrate the more likely electrons are to collide with them and slow down.

Experiment 1c: Diode or LED

Variables

Independent Variable: The potential difference across the diode.

Dependent Variable: The current through the diode

Method

Connect an ammeter in series with the diode to measure current through the diode. Connect a voltmeter in parallel with the diode to measure the potential difference across it. Use a variable resistor in series with the diode to vary the potential difference across the diode. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current.

Improving Precision

Use the same component for each repeat. Do not just use the same value of component as they may be slightly different from one another.

Use a low current and turn the circuit off between readings. This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings.

Results

Conclusion

Description

The IV Graph for a diode shows that:

• For a positive potential difference the current increases rapidly with an increase in potential difference
• For a negative potential difference the current remains negligible and does not increase as the potential difference becomes larger.

Explanation

The resistance of a diode is very low for current in the forward direction and very high in the back direction.

Experiment 1d: 'NTC' Thermistor

Variables

Independent Variable: The potential difference across the thermistor.

Dependent Variable: The current through the thermistor

Method

Connect an ammeter in series with the thermistor to measure current through the thermistor. Connect a voltmeter in parallel with the thermistor to measure the potential difference across it. Use a variable resistor in series with the thermistor to vary the potential difference across the thermistor. Place the thermistor in a beaker of cold water around 5°C. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current. Repeat steps 5-7 with the thermistor in a beaker of hot water around 40°C.

Improving Precision

Use the same component for each repeat. Do not just use the same value of component as they may be slightly different from one another.

Use a low current and turn the circuit off between readings. This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings.

Results

Conclusion

Description

The IV Graph for an 'NTC' thermistor shows that:

• At a high temperature the current increases rapidly with the potential difference
• At a low temperature the current increases slowly with the potential difference.

Explanation

The resistance of an 'NTC' thermistor increases as the temperature decreases.

Experiment 1a: Resistor

Variables

Independent Variable: The potential difference across the light dependent resistor.

Dependent Variable: The current through the light dependent resistor

Method

Connect an ammeter in series with the LDR to measure current through the LDR. Connect a voltmeter in parallel with the LDR to measure the potential difference across it. Use a variable resistor in series with the LDR to vary the potential difference across the LDR. Cover the LDR so that very little light reaches its surface. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current. Repeat steps 5-7 while shining a constant bright light on the LDR

Improving Precision

Use the same component for each repeat. Do not just use the same value of component as they may be slightly different from one another.

Use a low current and turn the circuit off between readings. This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings.

Results

Conclusion

Description

The IV Graph for a light dependent resistor shows that:

• At a high light intensity the current increases rapidly with the potential difference
• At a low light intensity the current increases slowly with the potential difference.

Explanation

The resistance of an LDR increases as the light intensity decreases.