Potentiometer

A potentiometer wire of length 1 m is connected to a driver cell of emf 3 V as shown in the figure. When a cell of 1×5 V emf is used in the secondary circuit, the balance point is found to be 60 cm. On replacing this cell and using a cell of unknown emf, the balance point shifts to 80 cm.Calculate unknown emf of the cell.

• 1 V

• 1.5 V

• 3 V

• 2 V

• 2.2 V

The following graph shows the variation of terminal potential difference V, across a combination of three cells in series to a resistor, versus the current. Calculate the emf and internal resistance of each cell

• E = 6 V & r = 3 ohm

• E = 2 V & r = 1 ohm

• E = 6 V & r = 1 ohm

• E = 2 V & r = 3 ohm

• E = 1 V & r = 1 ohm

A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable resistor ‘R’. Plot a graph showing the variation of terminal potential ‘V’ with resistance R.

• 1

• 2

• 3

• 4

• 

Name the instrument used to measure the emf of a cell

• Voltmeter

• Ammeter

• Potentiometer

• Galvanometer

• Multimeter

Why potentiometer is preferred to Voltmeter for measurement of emf?

• long wire is used

• null method

• no special advantage

• Alloys are used in potentiometer wire

Name the material used for making potentiometer wire

• Copper

• Aluminium

• Brass

• Manganin

• silver

Essential condition for working of potentiometer circuit

• Positive terminal cells in the primary circuit and secondary circuit are connected to same point

• Emf of cell in the primary circuit has to be greater than that of a cell in the secondary circuit

• Connections must be neat and tight

• Current flowing through the wire must be constant

How to increase the sensitivity of a potentiometer?

• 1. Connect a resistance series to the primary circuit of the potentiometer

• 2. Use a cell of low emf in the primary circuit

• 3. Increase the length of the potentiometer wire

• only 1 & 2

• 1, 2 & 3

Copper wires are not used in the construction of potentiometer because

• low resistance

• high temperature coefficient

• low resistance & high temperature coefficient

• expensive

• non availability

What is the use of a potentiometer?

• 1. comparison of emf's of two primary cells

• 2. finding internal resistance of a cell

• 3. can be used as a variable resistor

• 1 & 2

• 1,2 & 3