Class 12 Physics 2024 Board Exam

A thin plastic rod is bent into a circular ring of radius R. It is uniformly charged with charge density $\lambda$. The magnitude of the electric field at its centre is :
(A) $\frac{\lambda }{2{ϵ}_{0}R}$
(B) Zero
(C) $\frac{\lambda }{4\pi {ϵ}_{0}R}$
(D) $\frac{\lambda }{4{ϵ}_{0}R}$

Two charged particles P and Q, having the same charge but different masses m${}_P$ and m${}_Q$, start from rest and travel equal distances in a uniform electric field $\vec{E}$ in time t${}_P$ and t${}_Q$ respectively. Neglecting the effect of gravity, the ratio $\frac{t_P}{t_Q}$ is :
(A) $\sqrt{\frac{m_P}{m_Q}}$
(B) $\sqrt{\frac{m_Q}{m_P}}$
(C) $\frac{m_P}{m_Q}$
(D) $\frac{m_Q}{m_P}$

The capacitance of a parallel plate capacitor having a medium of dielectric constant K = 4 in between the plates is C. If this medium is removed, then the capacitance of the capacitor becomes :
(A) 4C
(B) C
(C) C/4
(D) 2C

Electrons drift with speed v${}_d$ in a conductor with potential difference V across its ends. If V is reduced to V/2, their drift speed will become :
(A) v${}_d$/2
(B) v${}_d$
(C) 2 v${}_d$
(D) 4 v${}_d$

Three small charged spheres X, Y and Z carrying charges + q, – q and + q respectively are placed equidistant from each other, as shown in the figure. The spheres Y and Z are held in place. Initially X is also held in place, but is otherwise free to move. When X is released, the path followed by it will be :
(A) A
(B) B
(C) C
(D) D

Ten capacitors, each of capacitance 1 $\mu$F, are connected in parallel to a source of 100 V. The total energy stored in the system is equal to :
(A) 10${}^{-2}$ J
(B) 10${}^{-3}$ J
(C) 0.5 × 10${}^{-3}$ J
(D) 5.0 × 10${}^{-2}$ J

Consider the circuit shown in the figure. The potential difference between points A and B is :
(A) 6 V
(B) 8 V
(C) 9 V
(D) 12 V

In a uniform straight wire, conduction electrons move along + x direction. Let $\vec{E}$ and $\vec{j}$ be the electric field and current density in the wire, respectively. Then :
(A) $\vec{E}$ and $\vec{j}$ both are along + x direction.
(B) $\vec{E}$ and $\vec{j}$ both are along – x direction.
(C) $\vec{E}$ is along + x direction, but $\vec{j}$ is along – x direction.
(D) $\vec{E}$ is along – x direction, but $\vec{j}$ is along + x direction.

A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A. The magnetic moment of the loop will be :
(A) 0.7 Am${}^2$
(B) 1.54 Am${}^2$
(C) 2.10 Am${}^2$
(D) 3.5 Am${}^2$

The emf induced in a coil rotating in a magnetic field does not depend upon the following :
(A) Area of the coil
(B) Resistance of the coil
(C) Number of turns in the coil
(D) Angular speed of rotation of the coil