Request a call back

Write Kirchhoff's laws and establish the necessary balance condition for Wheatstone's bridge
Asked by divyabharti14042004 | 18 Jan, 2022, 02:52: PM Expert Answer
(a) Junction rule: At any junction, the sum of the currents entering the junction is equal to the
sum of currents leaving the junction

(b) Loop rule: The algebraic sum of changes in potential around any closed loop involving
resistors and cells in the loop is zero As an application of Kirchhoff’s rules consider the circuit shown in above figure, which is called the Wheatstone bridge.
The bridge has four resistors R1, R2, R3 and R4. Across one pair of diagonally opposite
points (A and C in the figure) a source is connected. This (i.e., AC) is called the battery arm.
Between the other two vertices, B and D, a galvanometer G (which is a device to detect currents) is connected.
This line, shown as BD in the figure, is called the galvanometer arm.

For simplicity, we assume that the cell has no internal resistance. In general there will be currents flowing across
all the resistors as well as a current Ig through G. Of special interest, is the case of a balanced bridge
where the resistors are such that Ig = 0. We can easily get the balance condition, such that there is no current through G.

In this case, the Kirchhoff’s junction rule applied to junctions D and B (see the figure) immediately gives us the
relations I1 = I3 and I2 = I4.

Next, we apply Kirchhoff’s loop rule to closed loops ADBA and CBDC. The first loop gives

–I1 R1 + 0 + I2 R2 = 0....................................(1)

Current through galavanometer is zero, Hence middle term zero in above eqn.(1)

Second loop gives, upon using I3 = I1, I4 = I2

I2 R4 + 0 – I1 R3 = 0  .....................................(2)

From Eqn. (1), we obtain, whereas from Eqn. (2), we obtain, Hence, we obtain the condition This last expression relating the four resistors is called the balance condition for the
galvanometer to give zero or null deflection
Answered by Thiyagarajan K | 18 Jan, 2022, 05:47: PM

## Concept Videos

CBSE 12-science - Physics
Find the potential at point J. Asked by nudratnigar | 10 May, 2022, 12:02: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by divyabharti14042004 | 18 Jan, 2022, 02:52: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
find the voltage across each resistor using kirchhoff rules Asked by carthi66 | 11 Nov, 2021, 02:49: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by umeshts142 | 13 Oct, 2021, 08:14: AM ANSWERED BY EXPERT
CBSE 12-science - Physics
Find the current in each resistor Asked by najeeb.razvi | 09 Aug, 2021, 06:45: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
Find the current in each branch of the circuit. Asked by hitanshu92 | 09 Jul, 2021, 10:22: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
i want full explanation of example 157 pls help me Asked by niveshpritmani | 02 Aug, 2020, 11:50: AM ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by sakshisharma23498 | 12 Jul, 2020, 09:55: PM ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by pranavhv99 | 12 Dec, 2019, 10:57: AM ANSWERED BY EXPERT
CBSE 12-science - Physics
Can anyone tell me the answer for this question Asked by tomarparikshit85 | 05 Mar, 2019, 06:50: PM ANSWERED BY EXPERT