Question: Q. 21. A cell of and internal resistance is connected to two external resistances and and a perfect ammeter. The current in the circuit is measured in four different situations :
(i) without any external resistance in the circuit
(ii) with resistance only
(iii) with and in series combination
(iv) with and in parallel combination.
The currents measured in the four cases are , 1.05 A, 1.4 A and 4.2 A, but not necessarily in that order. Identify the currents corresponding to the four cases mentioned above. A[Delhi I, II, III 2012]
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Solution:
Ans. Use the formulae and values come as follows :
(i)
(ii)
(iii)
(iv)
(i)
(ii)
(iii)
(iv)
AI Q. 22. In the circuit shown in the figure, find the current through each resistor.
A [Delhi I, II, III 2015]
Ans. Total emf in the circuit
Total resistance of the circuit
Hence current flowing in the circuit
Current flowing through the resistors :
Current through and is
Current through is
Current through is
[AI Q. 1. Derive the expression for the current density of a conductor in terms of the conductivity and applied electric field. Explain, with reason how the mobility of electrons in a conductor changes when the potential difference applied is doubled, keeping the temperature of the conductor constant. A [Delhi Comptt. I, II, III 2017]
Ans. Derivation of current density
Explanation with reason the change in mobility of electrons
Using Ohm’s law,
Potential difference , across the ends of a conductor of length ’ ‘, where field ’ ’ is applied is given by
But current density,
As potential is doubled, drift velocity also gets doubled, therefore, no change in mobility.
[CBSE Marking Scheme 2017]
