2011 WAEC Physics Practical You are provided with cells, a potentiometer, an ammeter, a voltmeter, a bulb, a key,...

WAEC 2011

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You are provided with cells, a potentiometer, an ammeter, a voltmeter, a bulb, a key, a jockey, and other necessary materials.

Measure and record the emf E of the battery.
Set up a circuit as shown in the diagram above.
Close the key K and use the jockey to make a firm contact at J on the potentiometer wire such that PJ = x = 10cm.
Take the record of the voltmeter reading V and the corresponding ammeter reading I.
Evaluate log V and log I.
Repeat the procedure for other values of x =20, 30. 40, 50, and 60cm.
Tabulate your readings.
Plot a graph with the log I on the vertical axis and log V on the horizontal axis.
Determine the slope, s, of the graph.
Determine the intercept, c, on the vertical axis.
State two precautions taken to ensure accurate results.

(b)i. How is the brightness of the bulb affected as x increases? Give a reason for your answer.

ii. List two electrical devices whose actions do not obey ohm's law

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Explanation

Observation/table of values

S/N	V(volts)	I(Amps)	Log V	Log I
1	0.790	0.030	-0.100	-0.520
2	0.690	0.240	-0.160	-0.620
3	0.600	0.180	-0.220	-0.740
4	0.600	0.120	-0.220	-0.920
5	0.500	0.060	-0.300	-0.220
6	0.300	0.060	-0.520	-0.220

Slope (s) = \(\frac{\bigtriangleup \text{log I}}{\bigtriangleup \text{log V}} = \frac{y_{2}-y_{1}}{x_{2}-x_{1}}\)

(s) = \(\frac{-0.4-(-1.4)}{-0.04-(-0.62)} = \frac{-0.4+1.4}{-0.04+0.62}\)

= \(\frac{1}{0.58}\)

s = 1.72

Graph Log I against Log V

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PRECAUTIONS; i

- Ensured clean/tight terminals
- Opened key when reading was not taken
- Avoided parallax error in ammeter/ voltmeter.
- Avoided sliding or jockey on the potentiometer wire M Zero error of voltmeter/ammeter were noted.

(b)i. The brightness of the bulb increases. Voltage/current through the bulb increases.

ii. The devices that do not obey ohm's law;