CBSE Class 12th Physics Question Paper Solved Last 10 Years With Solution

Class 12 Subject Physics Paper Set 5 with Solutions

---

Question 1: (Marks 1)

The relationship between Brewester angle ‘θ’ and the speed of light ‘v’ in the denser medium is –

(a) v tan θ = c

(b) c tan θ = v

(c) v sin θ = c

(d) c sin θ = v

---

Answer :

(a) v tanθ = c

---

Question 2: (Marks 1)

Photo diodes are used to detect

(a) radio waves

(b) gamma rays

(c) IR rays

(d) optical signals

---

Answer :

(d) Optical Signals

---

Question 3: (Marks 1)

The selectivity of a series LCR a.c. circuit is large, when

(a) L is large and R is large

(b) L is small and R is small

(c) L is large and R is small

(d) L = R

---

Answer :

(c) L is large and R is small

---

Question 4: (Marks 1)

---

Answer :

---

Question 5: (Marks 1)

The wavelength and intensity of light emitted by a LED depend upon

(a) forward bias and energy gap of the semiconductor

(b) energy gap of the semiconductor and reverse bias

(c) energy gap only

(d) forward bias only

---

Answer :

(a) Forward bias and energy gap of the semiconductor

---

Question 6: (Marks 1)

---

Answer :

(b) √2 r

---

Question 7: (Marks 1)

The electric flux through a closed Gaussian surface depends upon

(a) Net charge enclosed and permittivity of the medium

(b) Net charge enclosed, permittivity of the medium and the size of the Gaussian surface

(c) Net charge enclosed only

(d) Permittivity of the medium only

---

Answer :

(a) Net Charge enclosed and permittivity of the medium

---

Question 8: (Marks 1)

If photons of frequency v are incident on the surfaces of metals. A & B of threshold frequencies v/2 and v/3 respectively, the ratio of the maximum kinetic energy of electrons emitted from A to that from B is

(a) 2 : 3

(b) 3 : 4

(c) 1 : 3

(d) √3 : √2

---

Answer :

(b) 3:4

---

Question 9: (Marks 1)

The power factor of a series LCR circuit at resonance will be

(a) 1

(b) 0

(c) 1/2

(d) 1/ √2

---

Answer :

(a) 1

---

Question 10: (Marks 1)

A biconcave lens of power P vertically splits into two identical plano concave parts. The power of each part will be

(a) 2P

(b) P/2

(c) P

(d) P/ √2

---

Answer :

(b) P/2

---

Question 11: (Marks 1)

The physical quantity having SI unit NC–1 m is ________.

---

Answer :

Electrostatic potential difference/ Electric potential

---

Question 12: (Marks 1)

A copper wire of non-uniform area of cross-section is connected to a d.c. battery. The physical quantity which remains constant along the wire is ________

---

Answer :

Electric current

---

Question 13: (Marks 1)

A point charge is placed at the centre of a hollow conducting sphere of internal radius ‘r’ and outer radius ‘2r’. The ratio of the surface charge density of the inner surface to that of the outer surface will be ________.

---

Answer :

4:1

---

Question 14: (Marks 1)

The ________ , a property of materials C, Si and Ge depends upon the energy gap between their conduction and valence bands.

---

Answer :

Conductivity/ Resistivity

( Also give full credit if a student writes semiconducting nature)

---

Question 15: (Marks 1)

The ability of a junction diode to ________ an alternating voltage, is based on the fact that it allows current to pass only when it is forward biased.

---

Answer :

Rectify

---

Question 16: (Marks 1)

Define the term ‘current sensitivity’ of a moving coil galvanometer.

---

Answer :

---

Question 17: (Marks 1)

Depict the fields diagram of an electromagnetic wave propagating along positive X-axis with its electric field along Y-axis.

---

Answer :

---

Question 18: (Marks 1)

Write the conditions on path difference under which (i) constructive (ii) destructive interference occur in Young’s double slit experiment.

---

Answer :

---

Question 19: (Marks 1)

Plot a graph showing variation of induced e.m.f. with the rate of change of current flowing through a coil.

OR

A series combination of an inductor (L), capacitor (C) and a resistor (R) is connected across an ac source of emf of peak value E₀ and angular frequency (ω). Plot a graph to show variation of impedance of the circuit with angular frequency (ω).

---

Answer :

---

Question 20: (Marks 1)

---

Answer :

---

Question 21: (Marks 2)

Derive the expression for the torque acting on an electric dipole, when it is held in a uniform electric field. Identify the orientation of the dipole in the electric field, in which it attains a stable equilibrium.

OR

Obtain the expression for the energy stored in a capacitor connected across a dc battery. Hence define energy density of the capacitor.

---

Answer :

---

Question 22: (Marks 2)

Gamma rays and radio waves travel with the same velocity in free space. Distinguish between them in terms of their origin and the main application.

---

Answer :

Gamma rays are emitted by radioactive nuclei/produced in nuclear reactions. Radio waves are produced by accelerated /oscillating charges/LC circuit. Gamma rays are used for the treatment of cancer/in nuclear reactions. Radio waves are used in communication systems/radio or television communication systems/cellular phones.

(or any other correct applications)

---

Question 23: (Marks 2)

---

Answer :

(i) Intensity of light transmitted by P₁ remains unaffected when P₁ is rotated about the direction of propagation of light.

Justification: The intensity of unpolarized light transmitted by a Polaroid does not depend on the orientation of the Polaroid with respect to the direction of propagation of light.

(ii) The intensity of light transmitted by P₂ will vary from I₁ to zero.

Justification: As per Malus’ Law I = I₀ cos² θ

Where θ is the angle between the pass axis of the polaroid P₂ and the pass axis of polaroid P₁. As θ varies from 0⁰ to π / 2, I₂ will vary from I₁ to zero.

---

Question 24: (Marks 2)

A heavy nucleus P of mass number 240 and binding energy 7.6 MeV per nucleon splits in to two nuclei Q and R of mass numbers 110, 130 and binding energy per nucleon 8.5 MeV and 8.4 MeV, respectively. Calculate the energy released in the fission.

---

Answer :

B.E. of heavy nucleus P = 240 × 7.6 MeV=1824 MeV

B.E. of nucleus Q = 110×8.5 MeV=935 MeV

B.E. of nucleus R = 130×8.4 MeV=1092 MeV

Energy released

= [(935+1092)-1824] MeV

= [2027-1824] MeV

= 203 MeV

---

Question 25: (Marks 2)

---

Answer :

---

Question 26: (Marks 2)

Use Bohr’s model of hydrogen atom to obtain the relationship between the angular momentum and the magnetic moment of the revolving electron.

---

Answer :

---

Question 27: (Marks 2)

In a single slit diffraction experiment, the width of the slit is increased. How will the (i) size and (ii) intensity of central bright band be affected ? Justify your answer.

---

Answer :

---

Question 28: (Marks 3)

(a) Differentiate between electrical resistance and resistivity of a conductor.

(b) Two metallic rods, each of length L, area of cross A₁ and A₂, having resistivities p₁ and p₂ are connected in parallel across a d.c. battery. Obtain the expression for the effective resistivity of this combination.

---

Answer :

---

Question 29: (Marks 3)

Calculate the de-Broglie wavelength associated with the electron revolving in the first excited state of hydrogen atom. The ground state energy of the hydrogen atom is –13.6 eV.

---

Answer :

---

Question 30: (Marks 3)

---

Answer :

---

Question 31: (Marks 3)

What is a solar cell ? Draw its V-I characteristics. Explain the three processes involved in its working.

OR

Draw the circuit diagram of a full wave rectifier. Explain its working showing its input and output waveforms.

---

Answer :

---

Question 32: (Marks 3)

An optical instrument uses a lens of power 100 D for objective lens and 50 D for its eyepiece. When the tube length is kept at 25 cm. the final image is formed at infinity.

(a) Identify the optical instrument

(b) Calculate the magnification produced by the instrument.

---

Answer :

Objective lens with a power of 100 D, has a focal length of 1cm (very short focal length)

Eye piece, with a power of 50 D, has a focal length of 2cm (short focal length)

The optical instrument is therefore a compound microscope.

(Note: Award this one mark if a student writes directly compound microscope without justifying.)

When the final image is formed at infinity, the magnification of a compound microscope equals

---

Question 33: (Marks 3)

(a) Two point charges q₁ and q₂ are kept at a distance of r₁₂ in air. Deduce the expression for the electrostatic potential energy of this system.

(b) If an external electric field (E) is applied on the system, write the expression for the total energy of this system.

---

Answer :

---

Question 34: (Marks 3)

---

Answer :

---

Question 35: (Marks 5)

(a) Define the term ‘focal length of a mirror’. With the help of a ray diagram, obtain the relation between its focal length and radius of curvature.

(b) Calculate the angle of emergence (e) of the ray of light incident normally on the face AC of a glass prism ABC of refractive index √3. How will the angle of emergence change qualitatively, if the ray of light emerges from the prism into a liquid of refractive index 1.3 instead of air ?

OR

(a) Define the term ‘resolving power of a telescople’. How will the resolving power be effected with the increase in

(i) Wavelength of light used.

(ii) Diameter of the objective lens. Justify your answers.

(b) A screen is placed 80 cm from an object. The image of the object on the screen is formed by a convex lens placed between them at two different locations separated by a distance 20 cm. Determine the focal length of the lens.

---

Answer :

---

Question 36: (Marks 5)

(a) Show that an ideal inductor does not dissipate power in an ac circuit.

(b) The variation of inductive reactance (X_L) of an inductor with the frequency (f) of the ac source of 100 V and variable frequency is shown in the fig.

(i) Calculate the self-inductance of the inductor.

(ii) When this inductor is used in series with a capacitor of unknown value and a resistor of 10 Ω at 300 s^–1, maximum power dissipation occurs in the circuit. Calculate the capacitance of the capacitor.

OR

(a) A conductor of length ‘l’ is rotated about one of its ends at a constant angular speed ‘ω’ in a plane perpendicular to a uniform magnetic field B. Plot graphs to show variations of the emf induced across the ends of the conductor with (i) angular speed  and (ii) length of the conductor l.

(b) Two concentric circular loops of radius 1 cm and 20 cm are placed coaxially.

(i) Find mutual inductance of the arrangement.

(ii) If the current passed through the outer loop is changed at a rate of 5 A/ms, find the emf induced in the inner loop. Assume the magnetic field on the inner loop to be uniform.

---

Answer :

---

Question 37: (Marks 5)

(a) Write two important characteristics of equipotential surfaces.

(b) A thin circular ring of radius r is charged uniformly so that its linear charge density becomes λ. Derive an expression for the electric field at a point P at a distance x from it along the axis of the ring. Hence, prove that at large distances (x >> r), the ring behaves as a point charge.

OR

(a) State Gauss’s law on electrostatics and derive an expression for the electric field due to a long straight thin uniformly charged wire (linear charge density λ) at a point lying at a distance r from the wire.

(b) The magnitude of electric field (in NC^–1) in a region varies with the distance r(in m) as

E = 10 r + 5

By how much does the electric potential increase in moving from point at r = 1 m to a point at r = 10 m.

---

Answer :

CBSE Class 12th Physics Question Paper Solved Last 10 Years with Solution

Physics sample paper class 12, Physics previous year question paper class 12, cbse class 12 Physics sample paper, cbse class 12 Physics sample paper 2020, Physics sample paper class 12 2020, cbse sample paper 2020 class 12 Physics, class 12 Physics sample paper 2020, class 12 important questions Physics, cbse class 12 board exam Physics paper, Physics previous year question papers class 12 with solutions, Physics sample paper class 12 2019, cbse class 12 Physics question paper 2017 solved pdf, cbse class 12 Physics question paper 2018, class 12 Physics paper 2019, Physics question paper for class 12, cbse class 12 Physics paper 2019

Ncert Solution for class 6 to 12 download in pdf