Physics
WAEC 2008
You are provided with two resistance wires labeled and B, a1\(\Omega\) standard resistor Rx, and other necessary apparatus.
- Connect R\(_{x}\) in the left hand gap of the metre bridge, a length L= 100cm of wire A in the right hand gap, and the other apparatus as shown in the diagram above.
- Determine and record the balance point P on the bridge wire NQ.
- Measure and record l\(_{x}\) = NP and l\(_{y}\) = PQ.
- Evaluate R\(_{1}\) = \(\frac{I_{y}}{L_{x}}\) = R\(_{x}\)
- Repeat the procedure for four other values of L= 95, 85, 75 and 65cm. In each case, determine and record the balance point P and the length l\(_{x}\) and l\(_{y}\). Also, evaluate R\(_{1}\).
- Repeat the experiment with the second wire B. Obtain the balance points P and the values of and l\(_{x}\) and l\(_{y}\).
- Evaluate R\(_{1}\) = \(\frac{I_{y}}{L_{x}}\) = R\(_{x}\) in each case. Tabulate your readings.
- Plot a graph of R\(_{2}\) on the vertical axis against R\(_{1}\) on the horizontal axis.
- Determine the slope, s, of the graph.
- Evaluate k = \(\sqrt s \).
- State two precautions taken to obtain accurate results.
(b)i. State two advantages of using a potentiometer over a voltmeter for measuring the potential difference.
ii. Define the internal resistance of a cell.
Explanation
L(cm) |
Lx(cm) |
Ly(cm) |
R\(_{1}\)=Ly. L x R |
Lx\(_{1}\) |
Ly\(_{1}\) |
R\(_{2}\),(Ly/Lx)Rx |
100 |
5.2 |
95.0 |
18.3 |
21.5 |
78.3 |
3.64 |
95 |
6.0 |
94.0 |
15.7 |
22.6 |
77.8 |
3.44 |
85 |
6.5 |
94.0 |
14.5 |
22.8 |
76.4 |
3.35 |
75 |
7.8 |
93.1 |
12.0 |
23.4 |
75.6 |
3.23 |
65 |
8.5 |
95.5 |
11.2 |
24.3 |
75.2 |
3.10 |
k = s
s = 0.0903
k = 0.0903 = 0.3005
Precautions: I
- ensured keys were removed when not taking readings.
- ensured tight connections/clean terminals.
- avoided parallax errors in reading meter rule.
- ensured jockey did not scratch the resistance wire.
- avoided zero error of meter rule noted and corrected.
(b)i. Advantages of the potentiometer over the voltmeter
- High accuracy
- Null deflection (does not draw current at balance point).
- Range can be increased as required.
- No friction in moving parts.
ii. The internal resistance of a cell is the opposition to the current flow through (the electrolyte of) the cell.
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