Physics Class 12 NCERT Solutions: Chapter 3 Current Electricity Part 5

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Meter bridge circuit

Meter Bridge Circuit

Q: 10. (A) In a meter bridge , the balance point is found to be at from the end A, when the resistor is of . Determine the resistance of. Why are the connections between resistors in a Wheatstone or meter bridge made of thick copper strips?

(B) Determine the balance point of the bridge above if X and Y are interchanged.

(C) What happens if the galvanometer and cell are interchanged at the balance point of the bridge? Would the galvanometer show any current?

Answer:

A meter bridge with resistors X and Y is represented in the given figure.

Q 10 Image of Metre Bridge and Resistors

Q 10 Image of Metre Bridge and Resistors

(A) Balance point form end

Resistance of the resistor

Condition for the balance is given as,

Therefore, the resistance of resistor X is .

The connection between resistors in a Wheatstone or metre bridge is made of thick copper strips to minimize the resistance, which is not taken into consideration in the bridge formula.

(B) If X and Y are interchanged, then get interchanged.

The balance point of the bridge will be from A.

Therefore, the balance point is from A.

(C) When the galvanometer and cell are interchanged at the balance point of the bridge, the galvanometer will show no deflection. Hence, no current would flow through the galvanometer.

Q: 11. A storage battery of emf and internal resistance is being charged by a dc supply using a series resistor of . What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?

Answer:

Emf of the storage battery,

Internal resistance of the battery,

DC supply voltage,

Resistance of the resistor,

Effective voltage in the circuit

R is connected to the storage battery in series. Hence, it can be written as

Current flowing in the circuit, which is given by the relation,

Voltage across resistor R is given by the product,

DC supply voltage Terminal voltage of battery Voltage drop across

Terminal voltage of battery

A series resistor in a charging circuit limits the current drawn from the external source. The current will be extremely high in its absence. This is very dangerous.

Q: 12. In a potentiometer arrangement, a cell of emf gives a balance point at length of the wire. If the cell is replaced by another cell and the balance point shifts to , what is the emf of the second cell?

Answer:

Emf of the cell,

Balance point of the potentiometer,

The cell is replaced by another cell of emf

New balance point of the potentiometer,

The balance condition id given by the relation,

Therefore, emf of the second cell is .

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