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Question
What are the disadvantages of a potentiometer?
Solution
Disadvantages of a potentiometer over a voltmeter:
- A potentiometer is an indirect measurement instrument, whereas a voltmeter is a direct reading instrument.
- A potentiometer is unwieldy while a voltmeter is portable.
- Unlike a voltmeter, a potentiometer requires a standard source of emf and calibration to measure an unknown emf.
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RELATED QUESTIONS
Accuracy of potentiometer can be easily increased by ______.
Write two factors by which current sensitivity of a potentiometer can be increased.
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Figure shows a potentiometer with a cell of 2.0 V and internal resistance 0.40 Ω maintaining a potential drop across the resistor wire AB. A standard cell which maintains a constant emf of 1.02 V (for very moderate currents up to a few mA) gives a balance point at 67.3 cm length of the wire. To ensure very low currents drawn from the standard cell, very high resistance of 600 kΩ is put in series with it, which is shorted close to the balance point. The standard cell is then replaced by a cell of unknown emf ε and the balance point found similarly, turns out to be at 82.3 cm length of the wire.
(a) What is the value ε?
(b) What purpose does the high resistance of 600 kΩ have?
(c) Is the balance point affected by this high resistance?
(d) Is the balance point affected by the internal resistance of the driver cell?
(e) Would the method work in the above situation if the driver cell of the potentiometer had an emf of 1.0 V instead of 2.0 V?
(f) Would the circuit work well for determining an extremely small emf, say of the order of a few mV (such as the typical emf of a thermo-couple)? If not, how will you modify the circuit?
State the underlying principle of a potentiometer ?
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The net resistance of a voltmeter should be large to ensure that ______________ .
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A student uses the circuit diagram of a potentiometer as shown in the figure
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where 'i' is the current in the potentiometer
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stands for a variable resistance R′. R′ can vary from R0 to infinity. r is internal resistance of the battery (r << R << R0).
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