A cell of emf E and internal resistance r is connected across an external resistance R. Plot a graph showing the variation of P.D. across R, verses R.

AB is a potentiometer wire (Fig 3.4). If the value of R is increased, in which direction will the balance point J shift?

While doing an experiment with potentiometer (Fig 3.5) it was found that the deflection is one sided and (i) the deflection decreased while moving from one end A of the wire to the end B; (ii) the deflection increased. While the jockey was moved towards the end B.

(i) Which terminal +or –ve of the cell E₁, is connected at X in case (i) and how is E₁ related to E?

(ii) Which terminal of the cell E₁ is connected at X in case (ii)?

First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is ‘n’?

Let there be n resistors R₁ ............R_n with R_max = max (R₁......... R_n) and R_min = min {R₁ ..... R_n}. Show that when they are connected in parallel, the resultant resistance R_P< R_min and when they are connected in series, the resultant resistance R_S > R_max. Interpret the result physically.