Advertisements
Advertisements
Question
Write the principle of working of a potentiometer. Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a given cell.
Solution
The working principle of a potentiometer is based on Kirchhoff’s voltage law. According to this rule, the algebraic sum of changes in voltage around any closed loop involving resistors and cells in the loop is zero.
Let Φ be the potential drop per unit length in the potentiometer wire.
When only a cell is connected, the balance point is N1.
Appling Kirchhoff’s voltage law,
ε = Φ l1 [l1 = Length at which the balance point is achieved]
When some current is drawn using the resistance box, the balance point is achieved at N2.
V = Φl2
This gives,
`epsi/V = l_1 / l_2`
ε = I (r + R) [R = Resistance of the resistance box]
V = IR
This gives,
`epsi /V = (r+R)/R`
`r = R (l_1/l_2 - 1)`
The internal resistance of the cell can be determined by plugging-in the measured values of l1 and l2.
APPEARS IN
RELATED QUESTIONS
Figure shows a 2.0 V potentiometer used for the determination of internal resistance of a 1.5 V cell. The balance point of the cell in open circuit is 76.3 cm. When a resistor of 9.5 Ω is used in the external circuit of the cell, the balance point shifts to 64.8 cm length of the potentiometer wire. Determine the internal resistance of the cell.
The net resistance of a voltmeter should be large to ensure that ______________ .
A battery of emf 4 volt and internal resistance 1 Ω is connected in parallel with another battery of emf 1 V and internal resistance 1 Ω (with their like poles connected together). The combination is used to send current through an external resistance of 2 Ω. Calculate the current through the external resistance.
Find the equivalent resistance between the terminals of A and B in the network shown in the figure below given that the resistance of each resistor is 10 ohm.
A potentiometer wire is 4m long and potential difference of 3V is maintained between the ends. The emf of the cell, which balances against a length of 100 cm of the potentiometer wire is ____________.
The length of a wire of a potentiometer is 100 cm, and the e.m.f of its standard cell is E volt. It is employed to measure the e.m.f of a battery whose internal resistance is 0.5 `Omega` If the balance point is obtained at `l`= 30 cm from the positive end, the e.m.f of the battery is ____________.
where 'i' is the current in the potentiometer
AB is a wire of potentiometer with the increase in value of resistance R, the shift in the balance point J will be:
The instrument among the following which measures the e.m.f of a cell most accurately is ______
AB is a potentiometer wire (Figure). If the value of R is increased, in which direction will the balance point J shift?
Two cells of same emf but different internal resistances r1 and r2 are connected in series with a resistance R. The value of resistance R, for which the potential difference across second cell is zero, is ______.
