Class 12 Physics Important Questions

Here are the most important questions from Class 12 Physics for board exam preparation. Students can practice these to score better.

Q1: A particle moves with acceleration a = 2 m/s². Find velocity after 5s if initial velocity u = 0.

Answer: v = u + at = 0 + 2*5 = 10 m/s

Q2: State Ohm’s Law.

Answer: Current through a conductor is directly proportional to voltage across the conductor and inversely proportional to resistance, V = IR.

Q3: Define Newton's second law of motion.

Answer: Force on an object is equal to the mass times its acceleration, F = ma.

Q4: The potential energy of a mass m at height h is?

Answer: PE = mgh

Q5: Speed of light in vacuum?

Answer: c = 3 × 10^8 m/s

Q6: State the work-energy theorem.

Answer: The work done on an object is equal to the change in its kinetic energy.

Q7: Define electric current.

Answer: Rate of flow of charge through a conductor.

Q8: Ohm’s law formula for resistance R?

Answer: R = V/I

Q9: Formula for kinetic energy.

Answer: KE = ½ mv²

Q10: Unit of power in SI.

Answer: Watt (W)

Q11: Capacitance of a capacitor formula.

Answer: C = Q/V

Q12: Magnetic field due to a straight conductor.

Answer: B = μ₀I/(2πr)

Q13: Laws of reflection of light.

Answer: 1) Angle of incidence = angle of reflection, 2) Incident ray, reflected ray and normal lie in same plane

Q14: Lens formula.

Answer: 1/f = 1/v – 1/u

Q15: Define resonance in oscillations.

Answer: Maximum amplitude occurs when frequency of driving force equals natural frequency.

Q16: Power in electrical circuit.

Answer: P = VI

Q17: Ohm’s law in differential form.

Answer: J = σE

Q18: Energy stored in a capacitor.

Answer: U = ½ CV²

Q19: Wave equation in string.

Answer: v = √(T/μ)

Q20: Laws of motion application in daily life.

Answer: Examples: seatbelt, moving bus, falling objects

Here are the most important high-weightage questions from Class 12 Physics for board exam preparation. Practice these carefully as they are frequently repeated.

Q1: Derive the equation of motion for a particle moving with constant acceleration.  

Answer: Using v = u + at, s = ut + ½ at², v² = u² + 2as. Apply Newton's second law F = ma.

Q2: A particle of mass m is moving in a circle of radius r with velocity v. Derive expression for centripetal force.  

Answer: F = mv²/r

Q3: Derive formula for kinetic energy and potential energy for a freely falling body.  

Answer: KE = ½ mv², PE = mgh, total energy = KE + PE = constant

Q4: Derive Ohm’s law using microscopic model of current.  

Answer: V = IR; using J = σE, where J = current density, σ = conductivity

Q5: Derive the formula for work done by a force at an angle θ to the displacement.  

Answer: W = F * s * cosθ

Q6: Derive formula for energy stored in a capacitor.  

Answer: U = ½ CV²

Q7: Derive the lens formula using ray diagram.  

Answer: 1/f = 1/v – 1/u

Q8: Derive formula for frequency of a simple harmonic oscillator.  

Answer: ω = √(k/m), f = ω/2π

Q9: Derive expression for motion of a body on an inclined plane.  

Answer: a = g sinθ

Q10: Derive expression for magnetic field at a point due to a long straight conductor carrying current I.  

Answer: B = μ₀I / 2πr

Q11: Derive formula for wave speed on a stretched string.  

Answer: v = √(T/μ)

Q12: Derive expression for Doppler effect for sound.  

Answer: f' = f (v ± v₀)/(v ∓ vs)

Q13: Derive expression for resonance in series LCR circuit.  

Answer: At resonance, XL = XC, I = V/R

Q14: Derive the expression for radius of curvature of a curved mirror.  

Answer: R = 2f

Q15: Derive formula for time period of a simple pendulum.  

Answer: T = 2π √(l/g)

Q16: Explain laws of motion with numerical example – e.g., force on a moving bus, recoil of gun.  

Answer: F = ma, conservation of momentum

Here are extra important questions from Class 12 Physics that are highly likely to appear in board exams. Practice these carefully.

Q17: A particle of mass m slides down a frictionless inclined plane of height h. Derive expression for its velocity at the bottom.  

Answer: Using conservation of energy, mgh = ½ mv² → v = √(2gh)

Q18: A wire of length L and cross-sectional area A has resistivity ρ. Derive formula for its resistance.  

Answer: R = ρL/A

Q19: Derive the expression for torque on a current-carrying rectangular coil in a uniform magnetic field.  

Answer: τ = nIBA sinθ

Q20: Derive expression for electric field at a point on the axis of a circular ring of charge Q.  

Answer: E = (1/4πε₀) * (Qx)/(x² + R²)^(3/2)

Q21: Derive expression for displacement in a damped harmonic oscillator.  

Answer: x = A e^(-bt/2m) cos(ω't + φ)

Q22: Derive expression for frequency of oscillation of a mass-spring system.  

Answer: f = 1/(2π) √(k/m)

Q23: A convex lens forms an image at distance v of an object at distance u. Derive lens formula.  

Answer: 1/f = 1/v – 1/u

Q24: Derive expression for motion of a particle under centripetal acceleration.  

Answer: a_c = v²/r

Q25: Derive the relation between angular velocity and linear velocity.  

Answer: v = ωr

Q26: Derive formula for magnetic force on a moving charge in a magnetic field.  

Answer: F = q(v × B)

Q27: Derive the expression for induced emf in a coil due to changing magnetic flux.  

Answer: ε = - dΦ/dt (Faraday’s law)

Q28: Derive formula for electric potential due to a point charge.  

Answer: V = (1/4πε₀) * Q/r

Q29: Derive formula for drift velocity of electrons in a conductor.  

Answer: vd = I / (nAe)

Q30: Derive expression for moment of inertia of a solid cylinder about its axis.  

Answer: I = ½ MR²

Here are more important questions from Class 12 Physics that can help students score high marks in board exams.

Q31: A charged particle moves in a uniform magnetic field perpendicular to its velocity. Derive expression for radius of its circular path.  

Answer: r = mv / (qB)

Q32: Derive the expression for the kinetic energy of an electron accelerated through a potential difference V.  

Answer: KE = eV

Q33: Derive the expression for motion of a body on a frictionless horizontal surface under constant force.  

Answer: F = ma → s = ut + ½ at²

Q34: Derive formula for escape velocity of a body from Earth.  

Answer: v_e = √(2GM/R)

Q35: Derive the expression for the energy of photon using Planck’s equation.  

Answer: E = hν

Q36: Derive the formula for time period of oscillation of a torsional pendulum.  

Answer: T = 2π √(I/C), I = moment of inertia, C = torsional constant

Q37: Derive the expression for the electric field at a point due to a dipole on its axial line.  

Answer: E = (1/4πε₀) * (2p / r³)

Q38: Derive the expression for electric field at a point on equatorial line of a dipole.  

Answer: E = (1/4πε₀) * (p / r³)

Q39: Derive the formula for refractive index using critical angle.  

Answer: n = 1/sin c

Q40: Derive the formula for the focal length of combination of two thin lenses in contact.  

Answer: 1/f = 1/f₁ + 1/f₂

Q41: Derive the expression for displacement in simple harmonic motion using sin function.  

Answer: x = A sin(ωt + φ)

Q42: Derive expression for centripetal acceleration using angular velocity.  

Answer: a_c = ω²r

Q43: Derive expression for torque on a dipole in uniform electric field.  

Answer: τ = pE sinθ

Q44: Derive the formula for self-inductance of a solenoid.  

Answer: L = μ₀ n² A l

Q45: Derive the expression for frequency of oscillations of LC circuit.  

Answer: f = 1 / (2π√(LC))

Tips: Practice derivations carefully and remember formulas. These questions are repeated frequently in Class 12 Physics board exams and can help you score high marks.

Q1.

A body starts from rest and moves with acceleration 2 \, m/s^2. Find distance covered in 10 s.

Solution:

s = ut + \frac{1}{2}at^2

s = 0 + \frac{1}{2} \times 2 \times 10^2 = 100 \, m

Q2.

A mass of 2 kg moves with velocity 5 m/s. Find its kinetic energy.

Solution:

KE = \frac{1}{2}mv^2

KE = \frac{1}{2} \times 2 \times 25 = 25 \, J

Q3.

Find potential energy of a 5 kg mass placed at height 10 m.

(Take g = 10 \, m/s^2)

Solution:

PE = mgh = 5 \times 10 \times 10 = 500 \, J

Q4.

Find resistance of a wire of length 2 m and area 1 \times 10^{-6} m^2, resistivity 1.7 \times 10^{-8} \, \Omega m.

Solution:

R = \frac{\rho L}{A}

R = \frac{1.7 \times 10^{-8} \times 2}{1 \times 10^{-6}} = 0.034 \, \Omega

Q5.

Calculate current flowing when 220 V is applied across a resistance of 110 Ω.

Solution:

I = \frac{V}{R} = \frac{220}{110} = 2 \, A

Q6.

Find electric power consumed by an appliance of resistance 50 Ω connected to 220 V.

Solution:

P = \frac{V^2}{R}

P = \frac{220^2}{50} = 968 \, W

Q7.

Find charge on a capacitor of capacitance 10 μF connected to 12 V battery.

Solution:

Q = CV

Q = 10 \times 10^{-6} \times 12 = 120 \, \mu C

Q8.

Find energy stored in the capacitor of Q7.

Solution:

U = \frac{1}{2}CV^2

U = \frac{1}{2} \times 10 \times 10^{-6} \times 144 = 7.2 \times 10^{-4} \, J

Q9.

A charge of 2 C moves with velocity 3 m/s perpendicular to magnetic field 0.5 T. Find force.

Solution:

F = qvB

F = 2 \times 3 \times 0.5 = 3 \, N

Q10.

Find magnetic field at distance 0.2 m from a straight wire carrying 10 A current.

Solution:

B = \frac{\mu_0 I}{2\pi r}

B = \frac{4\pi \times 10^{-7} \times 10}{2\pi \times 0.2} = 1 \times 10^{-5} \, T

Q11.

An object is placed 20 cm from a convex lens of focal length 10 cm. Find image distance.

Solution:

\frac{1}{f} = \frac{1}{v} + \frac{1}{u}

\frac{1}{10} = \frac{1}{v} - \frac{1}{20}

v = 20 \, cm

Q12.

Find magnification in Q11.

Solution:

m = \frac{v}{u} = \frac{20}{-20} = -1

Q13.

Calculate wavelength of light of frequency 6 \times 10^{14} Hz.

Solution:

\lambda = \frac{c}{\nu} = \frac{3 \times 10^8}{6 \times 10^{14}}

\lambda = 5 \times 10^{-7} m

Q14.

Find energy of photon of frequency 5 \times 10^{14} Hz.

(h = 6.63 \times 10^{-34} Js)

Solution:

E = h\nu = 3.31 \times 10^{-19} J

Q15.

Calculate escape velocity of Earth.

(g = 9.8 m/s^2, R = 6.4 \times 10^6 m)

Solution:

v_e = \sqrt{2gR}

v_e = 11.2 \, km/

Q1.

A body starts from rest and moves with acceleration 2 \, m/s^2. Find distance covered in 10 s.

Solution:

s = ut + \frac{1}{2}at^2

s = 0 + \frac{1}{2} \times 2 \times 10^2 = 100 \, m

Q2.

A mass of 2 kg moves with velocity 5 m/s. Find its kinetic energy.

Solution:

KE = \frac{1}{2}mv^2

KE = \frac{1}{2} \times 2 \times 25 = 25 \, J

Q3.

Find potential energy of a 5 kg mass placed at height 10 m.

(Take g = 10 \, m/s^2)

Solution:

PE = mgh = 5 \times 10 \times 10 = 500 \, J

Q4.

Find resistance of a wire of length 2 m and area 1 \times 10^{-6} m^2, resistivity 1.7 \times 10^{-8} \, \Omega m.

Solution:

R = \frac{\rho L}{A}

R = \frac{1.7 \times 10^{-8} \times 2}{1 \times 10^{-6}} = 0.034 \, \Omega

Q5.

Calculate current flowing when 220 V is applied across a resistance of 110 Ω.

Solution:

I = \frac{V}{R} = \frac{220}{110} = 2 \, A

Q6.

Find electric power consumed by an appliance of resistance 50 Ω connected to 220 V.

Solution:

P = \frac{V^2}{R}

P = \frac{220^2}{50} = 968 \, W

Q7.

Find charge on a capacitor of capacitance 10 μF connected to 12 V battery.

Solution:

Q = CV

Q = 10 \times 10^{-6} \times 12 = 120 \, \mu C

Q8.

Find energy stored in the capacitor of Q7.

Solution:

U = \frac{1}{2}CV^2

U = \frac{1}{2} \times 10 \times 10^{-6} \times 144 = 7.2 \times 10^{-4} \, J

Q9.

A charge of 2 C moves with velocity 3 m/s perpendicular to magnetic field 0.5 T. Find force.

Solution:

F = qvB

F = 2 \times 3 \times 0.5 = 3 \, N

Q10.

Find magnetic field at distance 0.2 m from a straight wire carrying 10 A current.

Solution:

B = \frac{\mu_0 I}{2\pi r}

B = \frac{4\pi \times 10^{-7} \times 10}{2\pi \times 0.2} = 1 \times 10^{-5} \, T

Q11.

An object is placed 20 cm from a convex lens of focal length 10 cm. Find image distance.

Solution:

\frac{1}{f} = \frac{1}{v} + \frac{1}{u}

\frac{1}{10} = \frac{1}{v} - \frac{1}{20}

v = 20 \, cm

Q12.

Find magnification in Q11.

Solution:

m = \frac{v}{u} = \frac{20}{-20} = -1

Q13.

Calculate wavelength of light of frequency 6 \times 10^{14} Hz.

Solution:

\lambda = \frac{c}{\nu} = \frac{3 \times 10^8}{6 \times 10^{14}}

\lambda = 5 \times 10^{-7} m

Q14.

Find energy of photon of frequency 5 \times 10^{14} Hz.

(h = 6.63 \times 10^{-34} Js)

Solution:

E = h\nu = 3.31 \times 10^{-19} J

Q15.

Calculate escape velocity of Earth.

(g = 9.8 m/s^2, R = 6.4 \times 10^6 m)

Solution:

v_e = \sqrt{2gR}

v_e = 11.2 \, km/s

Q1.

A body starts from rest and moves with acceleration 2 \, m/s^2. Find distance covered in 10 s.

Solution:

s = ut + \frac{1}{2}at^2

s = 0 + \frac{1}{2} \times 2 \times 10^2 = 100 \, m

Q2.

A mass of 2 kg moves with velocity 5 m/s. Find its kinetic energy.

Solution:

KE = \frac{1}{2}mv^2

KE = \frac{1}{2} \times 2 \times 25 = 25 \, J

Q3.

Find potential energy of a 5 kg mass placed at height 10 m.

(Take g = 10 \, m/s^2)

Solution:

PE = mgh = 5 \times 10 \times 10 = 500 \, J

Q4.

Find resistance of a wire of length 2 m and area 1 \times 10^{-6} m^2, resistivity 1.7 \times 10^{-8} \, \Omega m.

Solution:

R = \frac{\rho L}{A}

R = \frac{1.7 \times 10^{-8} \times 2}{1 \times 10^{-6}} = 0.034 \, \Omega

Q5.

Calculate current flowing when 220 V is applied across a resistance of 110 Ω.

Solution:

I = \frac{V}{R} = \frac{220}{110} = 2 \, A

Q6.

Find electric power consumed by an appliance of resistance 50 Ω connected to 220 V.

Solution:

P = \frac{V^2}{R}

P = \frac{220^2}{50} = 968 \, W

Q7.

Find charge on a capacitor of capacitance 10 μF connected to 12 V battery.

Solution:

Q = CV

Q = 10 \times 10^{-6} \times 12 = 120 \, \mu C

Q8.

Find energy stored in the capacitor of Q7.

Solution:

U = \frac{1}{2}CV^2

U = \frac{1}{2} \times 10 \times 10^{-6} \times 144 = 7.2 \times 10^{-4} \, J

Q9.

A charge of 2 C moves with velocity 3 m/s perpendicular to magnetic field 0.5 T. Find force.

Solution:

F = qvB

F = 2 \times 3 \times 0.5 = 3 \, N

Q10.

Find magnetic field at distance 0.2 m from a straight wire carrying 10 A current.

Solution:

B = \frac{\mu_0 I}{2\pi r}

B = \frac{4\pi \times 10^{-7} \times 10}{2\pi \times 0.2} = 1 \times 10^{-5} \, T

Q11.

An object is placed 20 cm from a convex lens of focal length 10 cm. Find image distance.

Solution:

\frac{1}{f} = \frac{1}{v} + \frac{1}{u}

\frac{1}{10} = \frac{1}{v} - \frac{1}{20}

v = 20 \, cm

Q12.

Find magnification in Q11.

Solution:

m = \frac{v}{u} = \frac{20}{-20} = -1

Q13.

Calculate wavelength of light of frequency 6 \times 10^{14} Hz.

Solution:

\lambda = \frac{c}{\nu} = \frac{3 \times 10^8}{6 \times 10^{14}}

\lambda = 5 \times 10^{-7} m

Q14.

Find energy of photon of frequency 5 \times 10^{14} Hz.

(h = 6.63 \times 10^{-34} Js)

Solution:

E = h\nu = 3.31 \times 10^{-19} J

Q15.

Calculate escape velocity of Earth.

(g = 9.8 m/s^2, R = 6.4 \times 10^6 m)

Solution:

v_e = \sqrt{2gR}

v_e = 11.2 \, km/s

Q1. A body starts from rest and moves with acceleration 2 m/s². Find distance covered in 10 s.

Solution:

s = ut + ½at²

s = 0 + ½ × 2 × 10²

s = 100 m

Q2. A mass of 2 kg moves with velocity 5 m/s. Find its kinetic energy.

Solution:

KE = ½mv²

KE = ½ × 2 × 25

KE = 25 J

Q3. Find potential energy of a 5 kg mass placed at a height of 10 m. (g = 10 m/s²)

Solution:

PE = mgh

PE = 5 × 10 × 10

PE = 500 J

Q4. Find resistance of a wire of length 2 m, area 1 × 10⁻⁶ m² and resistivity 1.7 × 10⁻⁸ Ωm.

Solution:

R = ρL/A

R = (1.7 × 10⁻⁸ × 2) / (1 × 10⁻⁶)

R = 0.034 Ω

Q5. Calculate current when 220 V is applied across a resistance of 110 Ω.

Solution:

I = V/R

I = 220/110

I = 2 A

Q6. Find electric power consumed by a device of resistance 50 Ω connected to 220 V.

Solution:

P = V²/R

P = 220² / 50

P = 968 W

Q7. Find charge on a capacitor of capacitance 10 μF connected to 12 V battery.

Solution:

Q = CV

Q = 10 × 10⁻⁶ × 12

Q = 120 μC

Q8. Find energy stored in the capacitor of capacitance 10 μF connected to 12 V.

Solution:

U = ½CV²

U = ½ × 10 × 10⁻⁶ × 144

U = 7.2 × 10⁻⁴ J

Q9. A charge of 2 C moves with velocity 3 m/s perpendicular to a magnetic field of 0.5 T. Find force.

Solution:

F = qvB

F = 2 × 3 × 0.5

F = 3 N

Q10. Find magnetic field at a distance 0.2 m from a straight conductor carrying 10 A current.

Solution:

B = μ₀I / 2πr

B = (4π × 10⁻⁷ × 10) / (2π × 0.2)

B = 1 × 10⁻⁵ T

Q11. An object is placed at 20 cm from a convex lens of focal length 10 cm. Find image distance.

Solution:

1/f = 1/v + 1/u

1/10 = 1/v − 1/