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Quick Practice - Class 12 Physics (NCERT Core) Select any chapter below to test your conceptual understanding, electrodynamics, optics, and modern physics skills with 5 high-yield multiple-choice questions, instant scoring, and verified step-by-step solutions. Q1.When a glass rod is rubbed with silk, it acquires a positive charge because: Answer: (c) electrons are removed from it. Charging by friction involves the transfer of electrons only. The glass rod loses electrons to the silk, leaving it with a net positive charge.
Q2.The electrostatic force between two point charges separated by a distance r is F. If the distance between them is halved, the force becomes: Answer: (b) 4F. According to Coulomb's Law, F is inversely proportional to r2. If r becomes r / 2, the force becomes F / (1/2)2 = 4F.
Q3.Which of the following properties is not valid for electric field lines? Answer: (d) Field lines can pass through a conductor. Inside a static conductor, the electric field is zero, so electric field lines cannot penetrate or exist inside conductors.
Q4.The electric flux through a closed surface enclosing an electric dipole is: Answer: (c) Zero. An electric dipole consists of equal and opposite charges (+q and -q). The net charge enclosed by the surface is +q + (-q) = 0. By Gauss's Law, the total electric flux is zero.
Q5.Dimensional formula for permittivity of free space (ε0) is: Answer: (a) [M-1 L-3 T4 A2]. From Coulomb's Law F = (1 / (4πε0)) × (q1q2 / r2), rearranging for ε0 gives dimensions of (Charge)2 / (Force × Length2).
Q1.The electric potential at any point inside a charged spherical shell is: Answer: (b) Equal to that on its surface. Since the electric field inside a hollow charged conductor is zero, the potential remains constant throughout the interior and is equal to the surface potential V = q / (4πε0R).
Q2.If a dielectric slab is inserted between the plates of an isolated parallel plate capacitor, its capacitance: Answer: (a) Increases. Capacitance becomes C' = K × C, where K (>1) is the dielectric constant of the medium.
Q3.Equipotential surfaces corresponding to a uniform electric field in the x-direction are: Answer: (c) Planes parallel to the yz-plane. For a uniform field along x, the potential only varies with x. Thus, planes perpendicular to the x-axis (i.e., parallel to the yz-plane) are equipotential surfaces.
Q4.Energy stored in a capacitor of capacitance C charged to a potential V is given by: Answer: (b) (1/2)CV2. The electrostatic potential energy stored in a charged capacitor is U = (1/2)CV2 = Q2/(2C) = (1/2)QV.
Q5.Three capacitors each of capacitance C are connected in series. Their equivalent capacitance is: Answer: (d) C / 3. For n identical capacitors in series, the equivalent capacitance is Ceq = C / n. Here n = 3, so Ceq = C / 3.
Q1.Drift velocity vd of electrons in a metallic conductor is related to the electric field E as: Answer: (a) vd ∝ E. Since vd = (τe/m)E, the drift velocity is directly proportional to the applied electric field.
Q2.Kirchhoff's First Law (junction rule) is based on the conservation of: Answer: (c) Charge. Kirchhoff's Current Law states that the algebraic sum of currents meeting at a junction is zero, reflecting the conservation of electric charge.
Q3.Specific resistance (resistivity) of a metallic wire depends upon: Answer: (d) Nature of material and temperature. Resistivity is an intrinsic property of the material and does not depend on the dimensions (length or area) of the wire.
Q4.The temperature coefficient of resistance for a semiconductor is: Answer: (b) Negative. In semiconductors, resistance decreases as temperature increases due to a greater release of charge carriers, resulting in a negative temperature coefficient.
Q5.A potentiometer is preferred over a voltmeter for measuring EMF because: Answer: (a) It draws no current from the source at balance point. At the null point, no current flows through the galvanometer branch, making it act as an ideal voltmeter with infinite resistance.
Q1.The magnetic force F on a charge q moving with velocity v in a magnetic field B is given by: Answer: (b) F = q (v × B). The Lorentz magnetic force vector is given by the cross product of velocity and magnetic field multiplied by the charge: F = q(v × B).
Q2.A moving coil galvanometer can be converted into an ammeter by connecting a: Answer: (a) Low resistance (shunt) in parallel. To measure large currents without damaging the galvanometer, a small shunt resistance is connected in parallel so most current bypasses the meter.
Q3.The magnetic field at the center of a circular coil of radius R carrying current I is: Answer: (c) μ0I / (2R). Derived directly from Biot-Savart's Law for a complete circular loop at its center: B = (μ0I) / (2R).
Q4.Two parallel conductors carrying currents in opposite directions will: Answer: (b) Repel each other. Currents flowing in opposite directions in parallel wires generate repulsive magnetic forces between them.
Q5.The radius of the circular path of a charged particle in a uniform magnetic field is proportional to: Answer: (a) Momentum of the particle. From r = mv / (qB), the radius is directly proportional to linear momentum p = mv.
Q1.The magnetic dipole moment of a current loop is independent of: Answer: (d) Magnetic field in which it is placed. Magnetic dipole moment is M = NIA, which depends on current, area, and turns, but is an intrinsic property independent of external magnetic fields.
Q2.The magnetic susceptibility of a diamagnetic substance is: Answer: (c) Small and negative. Diamagnetic materials are repelled by magnets, and their susceptibility is a small negative value, independent of temperature.
Q3.Curie's Law states that magnetic susceptibility of a paramagnetic substance is inversely proportional to: Answer: (b) Absolute temperature (T). Curie's law gives χ = C / T, showing susceptibility decreases with rising temperature.
Q4.Ferromagnetic materials exhibit domains. Above which temperature do they become paramagnetic? Answer: (a) Curie temperature. Thermal agitation destroys domain alignment above the Curie point, transforming ferromagnets into paramagnets.
Q5.Earth's magnetic field always has a vertical component except at the: Answer: (c) Magnetic equator. At the magnetic equator, magnetic field lines are completely horizontal, making the vertical component zero and angle of dip equal to 0°.
Q1.Lenz's Law is a consequence of the law of conservation of: Answer: (b) Energy. Lenz's law ensures that induced current opposes the flux change that produced it. Work must be done against this magnetic force, which is converted into electrical energy, satisfying conservation of energy.
Q2.SI unit of magnetic flux is: Answer: (a) Weber. Magnetic flux is measured in Weber (Wb), whereas Tesla is the unit of magnetic field (flux density).
Q3.Self-inductance of a long solenoid depends on: Answer: (d) Geometry and core permeability. Self-inductance L = μ0n2Al depends strictly on physical dimensions (cross-sectional area, length, number of turns) and core material.
Q4.Eddy currents are produced when: Answer: (c) A bulk conductor is placed in a changing magnetic field. Changing magnetic flux induces circulating loop currents (eddy currents) inside bulk metallic blocks.
Q5.The dimensional formula for self-inductance L is: Answer: (b) [M L2 T-2 A-2]. From energy stored U = (1/2)LI2, dimension of L = [Energy] / [Current]2 = [M L2 T-2] / [A2].
Q1.In an AC circuit containing only a pure capacitor, the current: Answer: (a) Leads the voltage by 90 degrees (π/2 radians). In capacitive circuits, current reaches its peak quarter-cycle ahead of the voltage.
Q2.At resonance in a series LCR circuit, the power factor is equal to: Answer: (c) 1. At resonance, inductive reactance equals capacitive reactance (XL = XC), making impedance purely resistive. Thus, phase angle φ = 0, giving power factor cos(φ) = 1.
Q3.The rms value of an alternating current of peak value I0 is: Answer: (b) I0 / √2. Root mean square (RMS) current is Irms = I0 / √2 ≈ 0.707 I0.
Q4.Transformers work on the principle of: Answer: (a) Mutual induction. A changing current in the primary coil induces an EMF in the secondary coil via magnetic flux linkage between the two coils.
Q5.The resonant frequency of a series LCR circuit is given by: Answer: (c) ω0 = 1 / √(LC). Resonance occurs when XL = XC, meaning ωL = 1 / (ωC), solving to ω0 = 1 / √(LC).
Q1.Displacement current is produced by: Answer: (b) Time-varying electric field. Maxwell introduced displacement current id = ε0 (dΦE/dt) to account for continuity where electric fields change with time.
Q2.Which electromagnetic waves have the shortest wavelength? Answer: (d) Gamma rays. Gamma rays occupy the high-frequency end of the electromagnetic spectrum, corresponding to the shortest wavelengths.
Q3.Electromagnetic waves are transverse in nature because: Answer: (a) Electric and magnetic fields oscillate perpendicular to each other and to the wave propagation direction. This mutual perpendicularity of E, B, and velocity vector v defines transverse electromagnetic waves.
Q4.The speed of electromagnetic waves in a vacuum is given by: Answer: (c) 1 / √(μ0ε0). Derived from Maxwell's equations as the speed of light c = 1 / √(μ0ε0).
Q5.Which of the following waves are used in radar systems for aircraft navigation? Answer: (b) Microwaves. Due to their short wavelengths, microwaves can be directed into narrow beams, making them ideal for radar and aircraft navigation.
Q1.A convex lens of glass (refractive index 1.5) dipped in water (refractive index 1.33) will act as a: Answer: (a) Convex lens with increased focal length. Since the refractive index of glass is greater than that of water, the lens remains converging (convex), but its focal length increases because the relative refractive index decreases.
Q2.Critical angle for total internal reflection is maximum for which color of light? Answer: (d) Red. Critical angle sin(ic) = 1 / n. Since refractive index n is lowest for red light (shortest wavelength dispersion), its critical angle is the maximum.
Q3.The magnifying power of an astronomical telescope in normal adjustment is given by: Answer: (b) -fo / fe. In normal adjustment, the magnifying power is the ratio of objective focal length to eyepiece focal length: m = -fo / fe.
Q4.Apparent depth of a tank filled with water of refractive index 4/3 is 9 cm. What is its real depth? Answer: (c) 12 cm. Refractive index n = (Real Depth) / (Apparent Depth), so Real Depth = 4/3 × 9 = 12 cm.
Q5.The angle of minimum deviation for a thin prism of refractive index n and refracting angle A is: Answer: (a) (n - 1)A. For a thin prism, minimum deviation formula simplifies to δm = (n - 1)A.
Q1.In Young's double slit experiment, if the distance between slits is halved and screen distance is doubled, the fringe width becomes: Answer: (b) Four times. Fringe width β = λD / d. If D becomes 2D and d becomes d/2, new fringe width β' = λ(2D) / (d/2) = 4(λD / d) = 4β.
Q2.The phenomenon of bending of light around corners of an obstacle is called: Answer: (c) Diffraction. Diffraction is the bending of light waves around obstacles or apertures whose sizes are comparable to the wavelength of light.
Q3.According to Brewster's Law, when light is incident at the polarizing angle, the reflected and refracted rays are: Answer: (a) Perpendicular to each other (90 degrees). At Brewster's angle, the angle between the reflected ray and refracted ray is exactly 90°.
Q4.Unpolarized light passes through a polaroid. The intensity of the transmitted light is: Answer: (c) Half of the incident intensity. When unpolarized light passes through a single ideal polarizer, half the intensity is blocked, leaving I = I0 / 2.
Q5.Huygens' Principle states that every point on a wavefront acts as a source of: Answer: (b) Secondary spherical wavelets. Huygens' wavelet theory dictates that each point on a wavefront serves as a secondary disturbance center emitting spherical wavelets.
Q1.The De Broglie wavelength λ associated with a particle of momentum p is given by: Answer: (a) λ = h / p. De Broglie hypothesis links wave and particle nature via wavelength λ = h / p, where h is Planck's constant.
Q2.Threshold frequency for a photoelectric surface is v0. If incident light has frequency v (< v0): Answer: (c) No photoemission takes place. Photoelectric emission requires the incident frequency to be greater than or equal to the threshold frequency (v ≥ v0).
Q3.Stopping potential in a photoelectric experiment depends upon: Answer: (b) Frequency of incident light. Maximum kinetic energy and stopping potential depend strictly on the frequency of incoming photons, whereas photocurrent magnitude depends on intensity.
Q4.The rest mass of a photon is: Answer: (a) Zero. Photons are massless packets of energy that always travel at the speed of light in vacuum and have zero rest mass.
Q5.Davisson-Germer experiment proved: Answer: (d) Wave nature of electrons (matter waves). Electron diffraction observed in the Davisson-Germer experiment experimentally verified de Broglie's hypothesis of matter waves.
Q1.In Rutherford's alpha particle scattering experiment, most alpha particles passed straight through because: Answer: (b) Most of the space inside an atom is empty. Since most alpha particles suffered zero deflection, it proved that the vast majority of atomic volume is vacant space.
Q2.According to Bohr's model, the angular momentum of an electron in stationary orbits is quantized as: Answer: (a) L = nh / (2π). Bohr postulated that angular momentum mvr is an integral multiple of h / (2π).
Q3.Which spectral series of hydrogen lies entirely in the ultraviolet region? Answer: (c) Lyman series. Transitions ending at the ground state (n = 1) emit high-energy photons belonging to the ultraviolet spectrum (Lyman series).
Q4.The radius of the n-th Bohr orbit in a hydrogen atom is proportional to: Answer: (b) n2. Bohr orbit radius expression rn = (0.529 × n2 / Z) angstroms shows direct proportionality to n2.
Q5.Total energy of an electron in the ground state of hydrogen atom is: Answer: (d) -13.6 eV. Total energy En = -13.6 / n2 eV. For the ground state n = 1, energy is -13.6 eV.
Q1.Nuclear density is typically of the order of: Answer: (a) 1017 kg/m3. Nuclear density is extremely high and independent of mass number A, constant at approximately 2.3 × 1017 kg/m3.
Q2.The binding energy per nucleon is maximum for nuclei with mass number around: Answer: (c) 56 (Iron). Iron (Fe-56) has the highest binding energy per nucleon (≈ 8.8 MeV/nucleon), making it the most stable atomic nucleus.
Q3.Nuclear forces are: Answer: (b) Short-range, strong, charge-independent attractive forces. Nuclear forces act between nucleons regardless of charge over extremely short fermi ranges.
Q4.In a nuclear reactor, heavy water (D2O) is used as a: Answer: (a) Moderator. Heavy water slows down fast fission neutrons to thermal speeds so they can sustain the chain reaction efficiently.
Q5.Half-life T1/2 of a radioactive substance is related to its decay constant λ as: Answer: (d) T1/2 = 0.693 / λ. Derived from radioactive decay law: T1/2 = ln(2) / λ ≈ 0.693 / λ.
Q1.When an intrinsic semiconductor is doped with a pentavalent impurity, it becomes a: Answer: (b) n-type semiconductor. Pentavalent impurities (like Phosphorus or Arsenic) donate free electrons, creating an n-type semiconductor with electrons as majority carriers.
Q2.In a forward biased p-n junction diode, the depletion layer width: Answer: (a) Decreases. Forward biasing opposes the internal barrier potential, narrowing the depletion region and allowing major current flow.
Q3.Which logic gate gives a high (1) output only when all its inputs are low (0)? Answer: (c) NOR gate. A NOR gate output is high only when all inputs are 0 (the exact inverse of an OR gate).
Q4.In a common emitter transistor amplifier, current gain β is related to current gain α as: Answer: (a) β = α / (1 - α). Standard transistor relations show β = ΔIC / ΔIB = α / (1 - α).
Q5.A Zener diode is specifically designed to operate under: Answer: (d) Reverse bias breakdown region. Zener diodes are heavily doped diodes used as voltage regulators in the reverse breakdown region.
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