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CBSE Class 12-science Answered

(a) State the working principle of a potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primary cells. Obtain the required expression used forcomparing the emfs. (b) Write two possible causes for one sided deflection in a potentiometer experiment. Or (a) State Kirchhoff's rules for an electric network. Using Kirchhoff's rules, obtain the balance condition in terms of the resistances of four arms of Wheatstone bridge. (b) In the meterbridge experimental set up, shown in the figure, the null point 'D' is obtained at a distance of 40 cm from end A of the meterbridge write. If a resistance of 10 Ω is connected in series with R1, null point is obtained at AD = 60 cm. Calculate the values of R1 and R2.  
Asked by Topperlearning User | 28 Apr, 2015, 11:06: AM
answered-by-expert Expert Answer

(a)

 

 

(b)

 

 

Or

 

(a) Kirchhoff's First Law ? Junction Rule

The algebraic sum of the currents meeting at a point in an electrical circuit is always zero.

 

Let the currents be

Convention:

Current towards the junction ? positive

Current away from the junction ? negative

Wheatstone Bridge:

The Wheatstone Bridge is an arrangement of four resistances as shown in the following figure.

 

This is the required balanced condition of Wheatstone Bridge.

 

(b)

Answered by | 28 Apr, 2015, 01:06: PM
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