(a) You are provided with two resistance wires labelled: A and B, standard resistor, R\(_x\) = 1 \(\Omega\), metre bridge, cell of emf,E, Rheostat R\(_h\), galvanometer and apparatus as shown.
Use the circuit diagram above as a guide to perform the experiment.
(i) Connect R\(_x\) in the left-hand gap of the metre bridge, a length L = 100 cm of the wire in the right-hand gap and the other apparatus shown.
(ii) Determine and record the balance point P on the metre bridge wire NQ
(iii) Measure and record L\(_x\) = NP and L\(_y\) = PQ
(iv) Evaluate R\(_1\) = \(\frac{L_y}{L_x}R_x\)
(v) Repeat the procedure for four other values of L = 90cm, 80cm, 70cm, and 60cm. In each case, determine and record the balance point, P and evaluate R\(_1\)
(vi) Repeat the experiment with the second wire B. Obtain the balance point P and evaluate R\(_2\) in each case
(vii) Tabulate the readings
(viii) Plot a graph of R\(_2\) on the vertical axis and R\(_1\) on the horizontal axis
(ix) Determine the slope, s, of the graph
(x) Evaluate K = \(\sqrt{s}\)
(xi) State two precautions taken to ensure accurate results.
b(i) State two advantages of potentiometer over voltmeter for measuring potential difference
(ii) Define internal resistance of a cell.
Attached Figure / Diagram
Verified Correct Answer: .
Physical Principles & Numerical Solution
(vii)
L(cm)
L\(_x\)(cm)
L\(_y\)(cm)
R\(_1\) = (\(\frac{L_y}{L_x})R_x\)\(\Omega\)
L\(_{x2}\)
L\(_{y2}\)
R\(_2\) = \(\frac{L_{y2}}{L_{x2}}R_x\)\(\Omega\)
100.0
5.2
94.8
18.2
21.5
78.5
3.6
90.0
6.0
94.0
15.7
22.5
77.5
3.4
80.0
6.8
93.2
13.7
23.4
76.6
3.3
70.0
7.6
92.4
12.2
24.5
75.5
3.1
60.0
8.4
91.6
10.9
25.6
74.4
2.9
(viii) SEE THE GRAPH ABOVE
(ix) Slope = \(\frac{\Delta R_2}{\Delta R_1}\) = \(\frac{3.5 - 3.3}{17.0 - 14.6}\) = \(\frac{0.2}{2.4}\) = 0.083
(x) K = \(\sqrt{0.083}\) = 0.2881
(xi) I Tight connection/clean terminal was ensured II. Key removed when readings were not being taken.
b(i) I. A potentiometer can be used for measuring the internal resistance of a cell and also to compare the e.m.f. of two cells. II. A potentiometer gives the exact value of potential difference across any two points in a circuit.
(ii) It refers to the opposition to the flow of current offered by the cells and batteries themselves resulting in the generation of heat.
Source: Myschool Past Questions Archive (Record #72108)