Figure 3.33 shows a potentiometer with a cell of 2.0 V and internalresistance 0.40 W maintaining a potential drop across the resistorwire AB. A standard cell which maintains a constant emf of 1.02 V(for very moderate currents upto a few mA) gives a balance point at67.3 cm length of the wire. To ensure very low currents drawn fromthe standard cell, a very high resistance of 600 kW is put in serieswith it, which is shorted close to the balance point. The standardcell is then replaced by a cell of unknown emf e and the balancepoint found similarly, turns out to be at 82.3 cm length of the wire. (a) What is the value e ? (b) What purpose does the high resistance of 600 kW have? (c) Is the balance point affected by this high resistance? (d) Would the method work in the above situation if the driver cellof the potentiometer had an emf of 1.0V instead of 2.0V?(e) Would the circuit work well for determining an extremely smallemf, say of the order of a few mV (such as the typical emf of athermo-couple)? If not, how will you modify the circuit?

Figure 3.33 shows a potentiometer with a cell of 2.0 V and internalres

1.	Figure 3.33 shows a potentiometer with a cell of 2.0 V and internalresistance 0.40 W maintaining a potential drop across the resistorwire AB. A standard cell which maintains a constant emf of 1.02 V(for very moderate currents upto a few mA) gives a balance point at67.3 cm length of the wire. To ensure very low currents drawn fromthe standard cell, a very high resistance of 600 kW is put in serieswith it, which is shorted close to the balance point. The standardcell is then replaced by a cell of unknown emf e and the balancepoint found similarly, turns out to be at 82.3 cm length of the wire. (a) What is the value e ? (b) What purpose does the high resistance of 600 kW have? (c) Is the balance point affected by this high resistance? (d) Would the method work in the above situation if the driver cellof the potentiometer had an emf of 1.0V instead of 2.0V?(e) Would the circuit work well for determining an extremely smallemf, say of the order of a few mV (such as the typical emf of athermo-couple)? If not, how will you modify the circuit?
Answer» Figure 3.33 shows a potentiometer with a cell of 2.0 V and internalresistance 0.40 W maintaining a potential drop across the resistorwire AB. A standard cell which maintains a constant emf of 1.02 V(for very moderate currents upto a few mA) gives a balance point at67.3 cm length of the wire. To ensure very low currents drawn fromthe standard cell, a very high resistance of 600 kW is put in serieswith it, which is shorted close to the balance point. The standardcell is then replaced by a cell of unknown emf e and the balancepoint found similarly, turns out to be at 82.3 cm length of the wire. (a) What is the value e ? (b) What purpose does the high resistance of 600 kW have? (c) Is the balance point affected by this high resistance? (d) Would the method work in the above situation if the driver cellof the potentiometer had an emf of 1.0V instead of 2.0V?(e) Would the circuit work well for determining an extremely smallemf, say of the order of a few mV (such as the typical emf of athermo-couple)? If not, how will you modify the circuit?

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