List of top Physics Questions on Magnetic Effects of Current and Magnetism

Three long straight wires carrying current are arranged mutually parallel as shown in the figure. The force experienced by $15$ cm length of wire $Q$ is ________. ($ \mu_0 = 4\pi \times 10^{-7}\,\text{T m A}^{-1} $)

The energy of an electron in an orbit of the Bohr's atom is $-0.04 E_g$ where $E_g$ is the ground state energy. If $L$ is the angular momentum of the electron in this orbit and $h$ is the Planck's constant, then $\frac{2 \pi L{h}$ is _________} :}

The current passing through a conducting loop in the form of equilateral triangle of side $4\sqrt{3}$ cm is 2 A. The magnetic field at its centroid is $\alpha \times 10^{-5}$ T. The value of $\alpha$ is ___. (Given : $\mu_0 = 4\pi \times 10^{-7}$ SI units)

Two small balls with masses m and 2m are attached to both ends of a rigid rod of length d and negligible mass. If angular momentum of this system is L about an axis (A) passing through its centre of mass and perpendicular to the rod then angular velocity of the system about A is:

There are three long parallel wires in a plane as shown. Find the force on $15$ cm of length of the middle wire.

A current-carrying straight conductor produces a magnetic field. The direction of the field is given by:

(I) Write Ampere’s circuital law in mathematical form and explain the terms used.
(II) As the current-carrying solenoid is made longer, the magnetic field produced outside it approaches zero. Why?
(III) A flexible loop of irregular shape carrying current, when located in an external magnetic field, changes to a circular shape. Give reason.

A 1 cm segment of a wire lying along the x-axis carries a current of 0.5 A along the $ +x $-direction. A magnetic field $ \mathbf{B} = (0.4 \, \text{mT}) \hat{j} + (0.6 \, \text{mT}) \hat{k} $ is switched on in the region. The force acting on the segment is:

A rectangular loop carries a current of 1 A. A straight long wire carrying 2 A current is kept near the loop in the same plane as shown in the figure.

Find:
(i) the torque acting on the loop, and
(ii) the magnitude and direction of the net force on the loop.

Write vector form of Biot–Savart law.

The value of magnetic field at point $ O $ in the given figure is:

The least count of a screw gauge is 0.01 mm. If the pitch is increased by 75% and the number of divisions on the circular scale is reduced by 50%, the new least count will be:

A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of $ f_1 $ in air. Another plano-convex lens with first surface radius of curvature 3 cm has focal length of $ f_2 $ when it is immersed in a liquid of refractive index 1.2. If both the lenses are made of the same glass of refractive index 1.5, the ratio of $ f_1 $ and $ f_2 $ will be:

A thin plano-convex lens made of glass of refractive index 1.5 is immersed in a liquid of refractive index 1.2. When the plane side of the lens is silver coated for complete reflection, the lens immersed in the liquid behaves like a concave mirror of focal length 0.2 m. The radius of curvature of the curved surface of the lens is:

A car of mass $ m $ moves on a banked road having radius $ r $ and banking angle $ \theta $. To avoid slipping from the banked road, the maximum permissible speed of the car is $ v_0 $. The coefficient of friction $ \mu $ between the wheels of the car and the banked road is:

Consider the following statements:
A. The junction area of a solar cell is made very narrow compared to a photodiode.
B. Solar cells are not connected with any external bias.
C. LED is made of lightly doped p-n junction.
D. Increase of forward current results in a continuous increase in LED light intensity.
E. LEDs have to be connected in forward bias for emission of light.