TEST OF PRACTICAL KNOWLEDGE QUESTION You are provided with a potentiometer XY, a voltmeter, V, a standard resistor R, an accumulator, E a plug key, K, a joc...

Answer Details

Principle: This is a potentiometer experiment. The voltmeter reading V is taken for several balance lengths l along the wire XY, and both \( V^{-1} \) and \( l^{-1} \) are evaluated. A graph of \( V^{-1} \) against \( l^{-1} \) is a straight line of slope s, and \( k = \dfrac{1}{s} \) is evaluated from it.

Method (as instructed): Connect the circuit as shown, close the key, and touch the jockey at N so that l = XN = 15 cm; read V. Evaluate \( l^{-1} \) and \( V^{-1} \). Repeat for l = 25, 35, 45, 55, 65 cm, tabulate l, V, \( l^{-1} \), \( V^{-1} \), plot \( V^{-1} \) against \( l^{-1} \) from the origin, find the slope s, and evaluate \( k = 1/s \).

Two precautions:

• Press the jockey gently and briefly on the wire (do not drag it) to avoid altering or damaging the wire.
• Ensure all connections are clean and tight, and read the voltmeter avoiding parallax.

(b)(i) Four factors on which the resistance of a wire depends:

• The length of the wire (\( R \propto l \)).
• The cross-sectional area of the wire (\( R \propto 1/A \)).
• The nature (material/resistivity) of the wire.
• The temperature of the wire.

(b)(ii) Heat produced. Resistance: \( R = 0.02 \times 100 = 2\,\Omega \). Current: \( I = \dfrac{V}{R} = \dfrac{1.5}{2} = 0.75\,\text{A} \). Time: \( t = 1\,\text{minute} = 60\,\text{s} \). Heat produced: \[ H = VIt = 1.5 \times 0.75 \times 60 = 67.5\,\text{J}. \]