2010 WAEC Physics Practical You are provided with a voltmeter V, a chemical cell/ battery E; two standard resistors...

WAEC 2010

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You are provided with a voltmeter V, a chemical cell/ battery E; two standard resistors R, and R a potentiometer a key K a jockey, and other necessary materials.

Set up a circuit as shown in the diagram above.
Close the key K.
Make contact with the potentiometer wire AB using the jockey at a point C such that AC = x = 20cm
Read and record the voltmeter reading
Evaluate x\(^{-1}\) and v\(^{-1}\)
Repeat the procedure for other values of x= 30, 40, 50, 60 and 80cm.
Tabulate your readings.
Plot a graph with V\(^{-1}\) on the vertical axis and x\(^{-1}\) on the horizontal axis, starting both axes from the origin (0, 0).
Determine the:
(a) slope, s, of the graph;
(b) intercept, c, on the vertical axis.
State two precautions taken to ensure accurate results.

(b)i. State the two devices in which ohm's law does not apply.

ii. A current of 1 A is supplied to two resistors of resistance 2\(\Omega\) and 3\(\Omega\) connected in parallel. Calculate the current in each resistor.

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Explanation

x/cm	v/volt	x\(^{1}\)/cm\(^{-1}\)	v\(^{1}\)/volts\(^{-1}\)
20	0.15	0.050	6.667
30	0.20	0.033	5.000
40	0.30	0.025	3.333
50	0.40	0.020	2.500
60	0.50	0.016	2.000
80	0.60	0.013	1.667

Slope = \(\frac{6.667-1.667}{0.050-0.013} = \frac{5}{0.037}\)

= 135.135cm/volt
intercept = 0

Precautions;

- Tight connections /clean terminals was ensured
- Key removed when readings are not being taken.
- Parallex error avoided in reading voltmeter/ rule.
- Zero error noted and corrected for in the voltmeter/rule
- Dragging jockey along the wire avoided

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