In this experiment, you will connect a 1.00 m length of nichrome resistance wire along a metre rule. One crocodile clip is fixed at the 0.0 cm mark. You con...
Question 1 Report
In this experiment, you will connect a 1.00 m length of nichrome resistance wire along a metre rule. One crocodile clip is fixed at the 0.0 cm mark. You connects the wire in series with a 3.0 V battery, a switch and an ammeter. You uses a voltmeter to measure the potential difference between the fixed clip and a sliding contact placed at 20.0 cm, 40.0 cm and 60.0 cm along the wire. The ammeter reads 0.24 A throughout.
| Length / cm | V / V |
|---|---|
| 20.0 | 0.59 |
| 40.0 | 1.18 |
| 60.0 | 1.77 |
(a) Record the voltmeter reading when the contact is at 40.0 cm. [1]
(b) Record the ammeter reading during the experiment. [1]
(c) Calculate the resistance of 20.0 cm of wire using R = V / I. [1]
(d) Describe the relationship between the length of wire and the voltage across it. [1]
(e) Predict the voltmeter reading when the contact is at 80.0 cm. [1]
(f) State one precaution to keep the current constant during the experiment. [1]
(g) State why the wire should be kept straight along the ruler. [1]
Answer Details
(a) From the table, when the contact is at 40.0 cm, the voltmeter reading is \( V = 1.18 \) V. [1]
(b) The ammeter reading throughout the experiment is \( I = 0.24 \) A. [1]
(c) Resistance of 20.0 cm of wire:
\[ R = \frac{V}{I} = \frac{0.59}{0.24} = 2.46 \text{ }\Omega \approx 2.5 \text{ }\Omega \] [1]
The voltage across 20.0 cm (V = 0.59 V) is used with the constant current to find the resistance of that length of wire.
(d) The voltage is directly proportional to the length of wire. [1]
This can be seen from the data: at 20.0 cm, V = 0.59 V; at 40.0 cm (double the length), V = 1.18 V (double the voltage); at 60.0 cm (triple), V = 1.77 V (triple). The ratio V/L is constant.
(e) Predicted voltmeter reading at 80.0 cm:
Since voltage is proportional to length: \( V_{80} = \frac{80.0}{20.0} \times 0.59 = 4 \times 0.59 = \)2.36 V. [1]
(f) Take readings quickly and switch off between readings to prevent the wire from heating up, which would change its resistance and thus the current. [1]
(g) The wire should be kept straight to ensure the length measured on the ruler is the actual length of wire carrying current. If the wire is slack or curved, the effective length differs from the ruler reading, introducing a systematic error. [1]
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