Physics NCERT Exemplar Solutions Class 12th Chapter Three

Consider a simple circuit shown in figure stands for a variable resistance R'. R' can vary from R₀to infinity, r is internal resistance of the battery (r <(a) Potential drop across AB is nearly constant as R' is varied.
(b) Current through R' is nearly a constant as R' is varied.
(c) Current I depends sensitively on R'
(d) I ≥ V/r + R always;

Kirchhoff's junction rule is a reflection of
(a) Conservation of current density vector.
(b) Conservation of charge.
(c) The fact that the momentum with which a charged particle approaches a junction is unchanged (as a vector) as the charged particle leaves the junction.
(d) The fact that there is no accumulation of charges at a junction.

Which of the following characteristics of electrons determines the current in a conductor?
(a) Drift velocity alone
(b) Thermal velocity alone
(c) Both drift velocity and thermal velocity
(d) Neither drift nor thermal velocity

A metal rod of length 10 cm and a rectangular cross-section of 1 cm x 1/2 cm is connected to a battery across opposite faces. The resistance will be
(a) Maximum when the battery is connected across 1 cm x 1/2 cm faces
(b) Maximum when the battery is connected across 10 cm x 1 cm faces
(c) Maximum when the battery is connected across 10 cm x 1/2 cm faces
(d) Same irrespective of the three faces

Two cells of emfs approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm.4. 
(a) The battery that runs the potentiometer should have voltage of 8 V.
(b) The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.

(c) The first portion of 50 cm of wire itself should have a potential drop of 10 V.
(d) Potentiometer is usually used for comparing resistances and not voltages.

A resistance R is to be measured using a meter bridge, a student chooses the standard resistance S to be 100 Ω He finds the null point at l₁= 2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way?
(a) He should measure l₁, more accurately
(b) He should change S to 1000 ? and repeat the experiment
(c) He should change S to 3 ? and repeat the experiment
(d) He should have given up hope of a more accurate measurement with a meter bridge.

Two batteries of emf e1 and e2 (e2>e1) and internal resistance r1 and r2 respectively are connected in parallel as shown in fig

(a) Two equivalent emf e_eq of the cells is between e1 and e2 i.e. e1eq

(b) The equivalent emf e_eq is samller than e₁

(c) The e_eq is given by e_eq=e₁+e₂ always

(d) E_eq is independent of internal resistance r₁ and r₂

Consider a current carrying wire (current 7) in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remain unaffected. The agent that is essentially responsible for is
(a) Source of emf
(b) Electric field produced by charges accumulated on the surface of wire
(c) The charges just behind a given segment of wire which push them just the right way by repulsion
(d) The charges ahead.

Suppose there is a circuit consisting of only resistances and batteries. Suppose one is to double (or increase it to n-times) all voltages and all. resistances. Show that currents are unaltered. Do this for circuit of Examples 3, 7 in the NCERT Text Book for Class XII.

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 mm. Conductor B is a hollow tube of outer diameter 2 mm and inner diameter 1 mm. Find the ratio of resistance RA to RB