Q.No.13.9: - What is Wheatstone bridge? How it be used to determine an unknown resistance?

Q.No.13.9: - What is Wheatstone bridge? How it be used to determine an unknown resistance?

Ans: - Wheatstone bridge is used to determine unknown resistance of a wire. The circuit is consists of four resistances R₁, R₂, R₃, R₄ connected in such a way as to form a loop or mesh ABCDA. A battery of emf E is connected between points A and C. A galvanometer of resistance R_g is connected between the points B and D.

          When the bridge is balanced, it satisfied the following relation

                                        R₁/R₂      =       R₃/R₄

Or,                                   R₄           =        R₂.R₃/R₁

If the value of R₁, R₂, and R₃ are known then R₄ can be calculated. The galvanometer should not show any deflection by adjusting the potential between terminals B and D. (Sorry for Diagram. Pleas concert with Text Book for diagram.)

Q.No.13.7: - Describe a circuit which will give a continuously varying potential?

Q.No.13.7: - Describe a circuit which will give a continuously varying potential?

Ans: - A potential divider or potentiometer is a circuit which can give a continuously varying potential. Consider a resistance R in the form of a wire on which a terminal C can slide. The resistance between A and C can be varied from 0 to R, as C slides from A to B.

          If we connect a battery of emf E across a resistance R. The current flowing thought it is

                                                  I        =        E/R

If we represent the resistance between A and C by r, the potential drop between these points will be

                                                  V        =        rI

Now,

                                                  V        =        r x E/R

Thus as C slides from A to B, r varies from 0 to R, and the potential drop between A and C changes from zero to E. This arrangement by which potential can be varied continuously from 0 to E is known as a potential divider.   (Sorry for Diagram. Pleas concert with Text Book for diagram.)