RE-NEET Physics Class 12 Questions

Three identical p-n junction diodes D₁, D₂ and D₃ are connected across a battery as shown in the figure. If the width of the depletion regions of D₁, D₂ and D₃ are W₁, W₂ and W₃, respectively, then the correct option is:

An electromagnetic wave travelling in a lossless dielectric medium having a dielectric constant, εᵣ=9, has the electric field, Eₓ=E₀sin (kz^{-2}π×10⁶t) Vm⁻¹ where E₀ is the amplitude and k is the wave vector. Among the following options, the incorrect choice is:

Consider three media P, Q and R with refractive indices 1, 1.25, and 1.5, respectively. The medium Q having a thickness of 5 cm is placed between extended media P and R as shown in the figure. An object O is placed at the center of medium Q. If viewed from medium P near the normal direction, the apparent depth of O is h₁. For similar observation from medium R, the apparent depth is h₂. The value of |h₁−h₂|, in cm, is:

Two infinitely long parallel conducting wires A and B carry currents I and 2I, respectively, in the same direction. The wire A has uniform mass per unit length λ and lies on an insulated floor. The wire B is kept fixed at a height h above the floor. The minimum magnitude of h so that the wire A does not rise from the floor is : [g is the acceleration due to gravity and μ₀ is the permeability of free space.]

A beam of light falls on a metal surface such that photo-electrons are generated. If power of the light source starts to decrease linearly with time t, then variation of the photocurrent I and magnitude of the stopping potential |V| with time is best represented by :

A unit positive point charge is taken slowly through an infinitesimally thin tube that is inside a charged dielectric tube that is inside a charged dielectric sphere of radius R, having uniform positive charge density ρ, as shown in the figure. The initial and final positions of the charge are marked by A and B at distances 2R and 3R respectively, from the centre of the sphere. In this process, the magnitude of the total work done on the point charge is \( \frac{\rho R^2}{n \varepsilon_0} \). The value of n is (\( \varepsilon_0 \) is the permittivity of vacuum).

The following table presents the parts of the electromagnetic spectrum and their corresponding major applications.

A point charge Q is placed inside a cavity within a solid isolated conducting sphere. Consider points A, B and C as shown in the figure, where the magnitudes of the electric fields are Eₐ, E_b and E_c respectively. The points B and C are at the same distance from the center of the solid sphere. The correct option is:

A current I₀ flows through a metallic circular loop of radius r as shown in the figure. Resistance of the segment ABC is half that of ADC. Magnitude of magnetic field at the center O of the loop is:

The lens combination as shown in the figure, consists of two lenses, L₁ and L₂, of the focal lengths +10 cm and^{-10} cm, respectively. The position of the image formed is:

An ideal Zener diode with breakdown voltage of^{-3} V is reverse biased with a negative input voltage Vᵢ = -5 V. The magnitude of voltage difference between points B and A is:

Three identical capacitors P, Q and S, each of the capacitance C, are connected to a battery of voltage V, as shown in the figure. If the energy stored in the capacitor P and total energy stored in the system are Uₚ and Uₜ, respectively, then the ratio Uₚ/Uₜ is:

A conducting loop of finite resistance lies on the x-y plane. There is a constant magnetic field in the z direction. The area of the loop varies with time t, as A = A₀(¹⁺ sin t) in appropriate units. The figure that correctly indicates the qualitative behaviour of the power P dissipated in the loop as a function of time is:

Consider two circuits, (A) and (B), each having two resistors. One of them has a positive temperature coefficient of resistance, +α, while the other one has a negative temperature coefficient, -α, as shown in the figure. The current I_A and I_B. At initial temperature, the resistance of the two resistors is R₀. As the temperature is increased, the correct option that describes the variation of current in these circuits is:

Consider a long solenoid of length l and radius r. If n is the number of turns per unit length and μ₀ is the permeability of free space, the inductance of the solenoid is:

Which of the following measurements require 'index correction'?

Two identical inductors are connected in two different configurations P and Q, where a time varying current I(t) is flowing, as shown in the figure. The induced emf between points a and b for configuration P is Eₚ and that for configuration Q is Eₚ. The ratio Eₚ/Eₚ is : [Neglect the effect of mutual inductance.]

In the circuit shown below, the inductance L is connected to an ac source. The current flowing in the circuit is I = I₀sinωt. The voltage drop (Vₗ) across L is

A uniform wire of diameter d carries a current of 100 mA when the mean drift velocity of electrons in the wire is v. For a wire of diameter d/2 of the same material to carry a current of 200 mA, the mean drift velocity of electrons in the wire is

In an electrical circuit, the voltage is measured as V = (200 ± 4) volt and the current is measured as I = (20 ± 0.2) A. The value of the resistance is:

A step up transformer is connected to an ac mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer, is

The I⁻V characteristics shown above are exhibited by a:

The magnetic moment and moment of inertia of a magnetic needle as shown are, respectively, 1.0 × 10⁻² A m² and 10⁻⁶/π² kg m². If it completes 10 oscillations in 10 s, the magnitude of the magnetic field is:

Given below are two statements: Statement I: Image formation needs regular reflection and/or refraction. Statement II: The variety in colour of objects we see around us is due to the constituent colours of the light incident on them. In the light of the above statements, choose the most appropriate answer from the options given below:

A uniform metal wire of length l has 10 Ω resistance. Now this wire is stretched to a length 2l and then bent to form a perfect circle. The equivalent resistance across any arbitrary diameter of that circle is:

Two slits in Young’s double slit experiment are 1.5 mm apart and the screen is placed at a distance of 1 m from the slits. If the wavelength of light used is 600 × 10⁻⁹ m then the fringe separation is

Let us consider two solenoids A and B, made from same magnetic material of relative permeability μᵣ and equal area of cross-section. Length of A is twice that of B and the number of turns per unit length in A is half that of B. The ratio of self inductances of the two solenoids, Lₐ : Lᵦ is

Interference pattern can be observed due to superposition of the following waves: A. y = a sinωt B. y = a sin2ωt C. y = a sin(ωt − ϕ) D. y = a sin3ωt Choose the correct answer from the options given below.

The electromagnetic radiation which has the smallest wavelength are

If the ratio of relative permeability and relative permittivity of a uniform medium is 1 : 4. The ratio of the magnitudes of electric field intensity (E) to the magnetic field intensity (H) of an EM wave propagating in that medium is

A beam of unpolarized light of intensity I₀ is passed through a polaroid A, then through another polaroid B, oriented at 60° and finally through another polaroid C, oriented at 45° relative to B as shown. The intensity of emergent light is:

The given circuit shows a uniform straight wire AB of 40 cm length fixed at both ends. In order to get zero reading in the galvanometer G, the free end of J is to be placed from B at:

The amplitude of the charge oscillating in a circuit decreases exponentially as Q = Q₀e⁻ᴿᵗ/²ᴸ, where Q₀ is the charge at t = 0s. The time at which charge amplitude decreases to 0.50 Q₀ is nearly: [Given that R = 1.5 Ω, L = 12 mH, ln(2) = 0.693]

The steady state current in the circuit shown below is: