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An experiment was set up to find the resistivity of the material of a wire - Leaving Cert Physics - Question 4 - 2018
Question 4
An experiment was set up to find the resistivity of the material of a wire. (i) Draw a labelled diagram of the apparatus used in this experiment. (ii) What measure... show full transcript
Worked Solution & Example Answer:An experiment was set up to find the resistivity of the material of a wire - Leaving Cert Physics - Question 4 - 2018
Step 1
Draw a labelled diagram of the apparatus used in this experiment.
Answer
To draw the apparatus, one should include the following components:
- Power Supply: A source of current.
- Ammeter: To measure the current flowing through the wire.
- Voltmeter: To measure the voltage across the wire.
- Wire: The wire material whose resistivity is being tested, marked with its length and diameter.
- Rheostat: To adjust the current.
Label each component clearly and indicate connections with lines.
Step 2
What measurements were taken during this experiment?
Answer
During this experiment, the following measurements were recorded:
- Current (I): Measured using the ammeter, which provides the flow of charge in the wire.
- Voltage (V): Measured across the wire using the voltmeter to find the potential difference.
- Length of the wire (L): The length of the wire from one end to the other, using a ruler or measuring tape.
- Diameter (d): To find the cross-sectional area, the diameter can be measured using a micrometer or caliper.
Step 3
How were these measurements used to calculate the resistivity?
Answer
The resistivity ( ho) of the wire can be calculated using the formula:
ho = R \cdot \frac{A}{L}$$ where: - **R** is the resistance of the wire, calculated using Ohm's law, where $R = \frac{V}{I}$. - **A** is the cross-sectional area of the wire, calculated using the diameter: $$A = \pi \left( \frac{d}{2} \right)^2$$ - **L** is the length of the wire. This involves substituting the measurements into the formula after calculating R from the voltage and current.Step 4
State two precautions which the student might have taken to improve the accuracy of this experiment.
Answer
To enhance accuracy, the following precautions could be taken:
- Remove Kinks in the Wire: Ensure the wire is straight and free of bends, which could affect measurements by altering the length encountered by the current.
- Take Multiple Readings: Conduct several trials to minimize errors, recording voltage and current multiple times and averaging the results for improved precision.
- Check Calibration of Instruments: Regularly check that the ammeter and voltmeter are correctly calibrated to ensure accurate readings.