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 = E₀ sin(kz − 2π×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.]

An ac voltage V=220 sin(2×10³t) Volt is applied to a series LCR circuit. Then the current amplitude in this circuit is : (Given : L=10 mH, C=25μF, R=100 Ω)

Consider a fixed uniformly charged insulating sphere with radius R and total charge +Q. A point charge -q (q<<Q) with mass m is released from rest at a distance of 3R from the centre of the charged sphere. When the point charge reaches the surface of the sphere, its speed is : (ε₀ is the permittivity of vacuum, neglect gravitational forces).

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 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 E_A, 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 ray of light with wavelength λ is incident on three different photo-electric cells namely 1, 2 and 3. The threshold wavelength of these photo-electric cells are λ₁, λ₂, and λ₃, respectively and the magnitude of stopping potentials of these cells are V₁, V₂ and V₃, respectively. The relation between λ and threshold wavelengths are λ₁ < λ, λ₂ > λ and λ₃ >> λ. 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 through these circuits are denoted by 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 the following nuclear reaction: ²³⁸U → ²³⁴Th + ⁴He. Take masses of ²³⁸U, ²³⁴Th and ⁴He as 238.050 u, 234.043 u and 4.003 u, respectively. The Q value for the reaction, in keV, is: [Given: 1 u = 931.5 MeV c⁻²]

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'?

A photon and an electron, each of 20 eV energy, move in free space. The ratio of linear momentum of electron pₑ to that of photon p_ph is: (Take speed of light = 3×10⁸ ms⁻¹, charge of electron = -1.6×10⁻¹⁹ C and mass of electron = 9×10⁻³¹ kg)

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 E_P and that for configuration Q is E_Q. The ratio E_P/E_Q is : [Neglect the effect of mutual inductance.]

The magnetic potential energy, when a magnetic bar of magnetic moment $\vec{m}$ is placed perpendicular to the magnetic field $\vec{B}$ is

A metal cube of side 5 cm is charged with 6 µC. The surface charge density on the cube is

The incorrect relation for a diamagnetic material (all the symbols carry their usual meaning and $\varepsilon$ is a small positive number) is:

Q

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 12 pF capacitor is connected to a 50 V battery, the electrostatic energy stored in the capacitor in nJ 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:

The capacitance of a capacitor with charge q and a potential difference V depends on:

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

When the output of an OR gate is applied as input to a NOT gate, then the combination acts as a

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.

If ϕ is the work function of photosensitive material in eV and light of wavelength of numerical value λ = $\frac{hc}{e}$ metre, is incident on it with energy above its threshold value at an instant then the maximum kinetic energy of the photo-electron ejected by it at that instant (Take h-Planck’s constant, c-velocity of light in free space) is (in SI units):

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

The value of electric potential at a distance of 9 cm from the point charge 4 × 10⁻⁷ C 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:

Select the correct statements among the following:

A. Slow neutrons can cause fission in ²³⁵U than fast neutrons.

B. α-rays are Helium nuclei.

C. β-rays are fast moving electrons or positrons.

D. γ-rays are electromagnetic radiations of wavelengths larger than X⁻rays. Choose the most appropriate answer from the options given below:

The magnetic moment of an iron bar is M. It is now bent in such a way that it forms an arc section of a circle subtending an angle of 60° at the centre. The magnetic moment of this arc section 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 output Y for the inputs A and B of the given logic circuit is:

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]