CBSE Class 12 Physics — MCQs

In an unbiased p-n junction, at equilibrium, which of the following statements is true?

In a region, the electric potential varies as $V = 10 - 50x$, where V is in volts and x in meters. The electric field in the region is:

A conducting wire connects two charged metallic spheres A and B of radii $r_1$ and $r_2$ respectively. The distance between the spheres is very large compared to their radii. The ratio of electric fields, ($E_A/E_B$) at the surfaces of spheres A and B will be

A long straight wire of circular cross-section (radius a) carries a steady current I. The current is uniformly distributed across this cross-section. The magnitude of the magnetic field produced at a point at a distance $(a/2)$ from the axis of the wire will be

An electromagnetic wave passes from vacuum into a dielectric medium with relative electrical permittivity $(3/2)$ and relative magnetic permeability $(8/3)$. Then, its

In a series LCR circuit, the voltage across the resistor, capacitor and inductor is 10 V each. If the capacitor is short circuited, the voltage across the inductor will be

Electromagnetic waves used in a diagnostic tool in medicine have a wavelength range

The 'distance of closest approach' of an alpha-particle is 'd' when it moves with a velocity v head-on towards the target nucleus. If the velocity of alpha particle is halved, the new 'distance of closest approach' will be −

A concave lens of focal length 10 cm is cut into two identical plano-concave lenses. The focal length of each lens will be

Four independent waves are expressed as (i) $y_1 = A_1 \sin \omega t$ (ii) $y_2 = A_2 \sin 2\omega t$ (iii) $y_3 = A_3 \cos \omega t$ (iv) $y_4 = A_4 \sin (\omega t + \pi/3)$. The interference between two of these waves is possible in

Two heaters rated as $(P_1, V)$ and $(P_2, V)$ are connected in series across a dc source of $V/2$ volt. The power consumed by the combination will be −

The torque on the coil remains constant irrespective of the coil's orientation during rotation due to

The best way to increase current sensitivity of a galvanometer is by

A moving coil galvanometer has a coil with area of cross-section $4.0 \times 10^{-3} \text{ m}^2$ and number of turns 50. The coil is rotating in a magnetic field of 0.25 T. The torque acting on the coil when a current of 5 A passes through it is OR A galvanometer coil has a resistance of 15 Ω and the meter shows full scale deflection for a current of 3 mA. The value of resistance required to convert it into a voltmeter of range (0 – 12 V) is (A) 4015 Ω (B) 3985 Ω (C) 415 Ω (D) 385 Ω

A galvanometer with coil of resistance 20 Ω shows full scale deflection for a current of 5 mA. To convert it into an ammeter of range (0 – 10 A), a resistance of

From the graph, the work functions of A and B are (h is Planck's constant and e value of charge on an electron)

For radiation of frequency $\nu > \nu_2$ incident on the surfaces of A and B, the maximum kinetic energy of ejected electron is

If the intensity of the incident radiation for both metals A and B, is doubled keeping its frequency constant, then

The shape of the interference fringes in Young's double-slit experiment, when the distance between the slit and the screen is very large as compared to the slit-separation, is nearly

The threshold frequency for a metal surface is $\nu_0$. If the radiation of frequency $3\nu_0$ illuminates the surface, the maximum kinetic energy (KE) of photoelectrons is $E_1$. If the frequency were increased to $6\nu_0$, the maximum KE of the photoelectrons becomes $E_2$. Then $(E_1/E_2)$ equals OR Let m be the slope of the graph line for metal B. If e is the value of electron charge, then Planck's constant 'h' is given by (A) $me$ (B) $1/(me)$ (C) $m/e$ (D) $e/m$