Most important physics questions for 12th class

Looking for the most important physics questions for 12th class? This comprehensive guide has got you covered! Get access to a carefully curated list of essential physics questions that will help you prepare for your exams and excel in your studies. From Electrostatics to Modern physics, this guide covers all the major topics that you need to know. Start preparing today and boost your confidence for the upcoming exams!

Electrostatics

1. What is quantization? Explain with example.
2. Why two lines of force never cross each other?
3. Derive an expression for electric field due to a dipole in equatorial position or broad side on position.
4. Derive an expression for torque acting on the dipole placed in uniform electric field.
5. Derive an expression for the electric field due to a long straight conductor having a linear charge density at a distance r from it.
6. Derive an expression for the electric field due to a infinite plane sheet of charge having a surface charge density
7. Why electric potential is constant inside a thin charged spherical shell?
8. Prove that electric lines of force are normal to the equipotential surfaces.
9. Derive an expression for the capacitance of a parallel plate capacitor partially filled with dielectric.
10. Explain why the capacity of the earth is infinite.
11. Derive an expression for the electrostatic potential energy of a parallel plate capacitor.
12. Draw a plot showing variation of electric potential V with distance r due to a point charge Q.
13. Deduce an expression for the potential energy of a system of two positive charges and located at positions and , in an electric field (E).
14. Draw the equipotential surface for an electric field pointing in with its magnitude increasing at constant rate along .
15. State Gauss’s law in electrostatics. Show that with the help of suitable figure that outward flux due to a point charge , in vacuum within gaussian surface, is independent of its size and shape.
16. An electric dipole of length is placed with its axis making an angle of with respect to uniform electric field of . It experiences a torque of , calculate (i) the magnitude of charge on the dipole and (ii) its potential energy.
17. What is capacitor ? Derive an expression of capacitance of the spherical capacitor. Draw necessary diagram.
18. Define electric potential. Obtain an expression of electric potential due to an electric dipole at any point (). Draw necessary diagram.
19. An electron is moving around an infinite linear charge in a circular path of diameter . If linear charge density is , then calculate the speed of an electron. ()
20. Define capacitor. Draw a circuit diagram and obtain a relation for equivalent capacitance for the series combination of three capacitors.
21. Write the statement of Gauss’s law for electrostatics. Derive an expression for electric field due to a uniformly charged infinite non-conducting sheet at a point near it. Draw suitable diagram.
22. Define : (a) Electric dipole moment. (b) Equipotential surface.

Current Electricity

1. Derive the electric current in terms of drift velocity.
2. Derive an expression for resistivity of a conductor.
3. Write the ohm’s law in vector form.
4. Obtain an expression for the equivalent emf and equivalent internal resistance of parallel combination of two cells.
5. State and explain Kirchhoff’s loop rule for an electric circuit.
6. State and explain working principle of a meter bridge.

8. Derive an expression for drift velocity.
9. At ${27}^{\circ }$, the resistance of a heating element is $\mathrm{100\Omega }$. At what temperature will its resistance be $\mathrm{117\Omega }$ ($\mathrm{\alpha =1.7\times 10-4/\circ C}$)
10. How does resistance of a conductor change with temperature?
11. Why potentiometer be preferred over a voltmeter for the measurement of emf of a cell ?

14. (a) Write Kirchhoff’s second law. (b) Draw a circuit diagram for comparison of emf of two primary cells with the help of potentiometer.
15. Three resistors are connected in parallel. The electric current 7.5 A is flowing in this combination from a battery of emf 30 V. If the values of two resistors are and then find the value of the third resistor.
16. Explain the method to find unknown resistance with the help of a meter bridge. Draw circuit diagram.
17. Derive the formula for obtaining the internal resistance of a primary cell with help of a potentiometer. Draw a circuit diagram.

Moving charges and Magnetism

1. Name the physical quantity having unit .
2. An electron with charge and mass travels at a speed in a plane perpendicular to a magnetic field of magnitude . The electron follows a circular path of radius . In a time , the electron travels halfway around the circle. What is the amount of work done by the magnetic field?
3. Describe the construction of suspended coil galvanometer, draw labelled diagram of it.Prove that current flowing in the coil of galvanometer is directly proportional to the deflection generated in the coil.
4. What is Helmholtz coils ? Prove that the value of a uniform magnetic field obtained in the Helmholtz coil is 1.432 times the magnetic field generated by each coil at its centre. Draw necessary graph also.
5. (a) The magnetic moment of two bar magnets are and . If angle between them is then write the value of resultant magnetic moment. (b) Soft iron is used in making electro-magnets. Why ?
6. (a) Write Biot-Savart law. (b) Write the working of cyclotron in brief. Draw a schematic sketch of the cyclotron showing path of accelerated charged particles (ions) in both dees. Derive expression for cyclotron frequency.
7. (a) Write Ampere’s law. (b) Draw a diagram and derive an expression for the magnetic field due to an infinitely long straight current-carrying conductor at any point.
8. The magnitude of the electric field at a point in free space is 300 V/m. Find the magnitude of magnetic field at this point. The velocity of light is .
9. (a) Define Curie temperature. (b) The pole strength of poles of a bar magnet of effective length 0.1 m is 40 A-m. Calculate it’s magnetic moment.
10. Define angle of dip. Write value of angle of dip at magnetic poles of earth.
11. Write formula for force on a current carrying conductor in a magnetic field.

Electromagnetic Induction

1. Obtain an expression for the induced emf generated due to the rotational motion of the rectangular coil in the uniform magnetic field. Draw a graph between induced emf and time .
2. Derive an expression for induced emf in a rod rotating in a uniform magnetic field. Draw the necessary diagram.
3. Write Lenz’s law. Lenz’s law obeys law of conservation of energy. Explain.

Alternating current

1. The voltage and current in an a.c. circuit are and respectively. Calculate : (i) Wattless current and (ii) Root mean square voltage.
2. The power factor of a coil is 0.707 at frequency 50 Hz. If frequency is doubled, then calculate the power factor of coil.
3. Draw a vector diagram (phasor diagram) for a series RLC circuit which is connected with an alternating voltage source and determine the expression for the impedance of the circuit.
4. In LCR alternating circuit, and . Write value of impedance of circuit.
5. Write the relation between the root mean square (RMS) value and the peak value of alternating current.

Electromagnetic waves

1. Mention on use of part of electromagnetic spectrum to which a wavelength of 21 cm (emitted by hydrogen in interstellar space) belogs.
2. Give the ratio of velocity of the two light waves of wavelengths and travelling in vacuum.
3. In electromagnetic waves, write the value of (A) angle and (B) phase difference, between electric field and magnetic field .

Ray optics and optical instruments

1. What is Presbyopia ? Describe the construction and working of reflecting telescope.Draw necessary ray diagram.
2. Focal length of a convex lens in air is 25 cm. If it is immersed in water, then calculate the focal length of the lens.
3. What do you understand by scattering of light ?
4. (a) Deduce an expression for mirror equation. Draw necessary ray diagram. (b) Find focal length of a spherical mirror of radius of curvature 10 cm.
5. Write definitions : (a) Total internal reflection. (b) Diffraction of light.
6. Write relation between power of lens and it’s focal length.

Wave optics

1. What is wave front ? Explain laws of refraction of light on the basis of Huygens wave theory. Draw necessary ray diagram.
2. Write any two differences between diffraction and interference of light.
3. (a) Draw a ray diagram to produce an interference fringe pattern in Young’s double slit experiment. Derive an expression for fringe width of bright fringes.(b) In Young’s double slit experiment, the fringe width is 2 mm. Find the distance of the second dark fringe from the central fringe.
4. (a) Write formula related to Malus law. (b) When light is incident at 60° on a transparent sheet, the reflected light is completely polarised. Find the refractive index of the substance and refraction angle.

Dual nature of Radiation and Matter

1. Why photo-electric effect cannot be explained on the basis of wave theory of light ? Write any two reasons.
2. What was the main objective of Davisson and Germer experiment.
3. Calculate de Broglie wavelength of a wave associated with an electron, which is accelerated through a potential difference of 100 V.
4. Draw diagram of the experimental arrangement of Davisson and Germer experiment.
5. Define threshold frequency.

Atoms

1. Explain Bohr’s second postulate with the help of De-Broglie’s hypothesis. Draw a stationary wave model of an electron for orbit n = 3.
2. Write Heisenberg’s uncertainty principle.
3. Write Niels Bohr’s any two postulates for hydrogen atom (hydrogen like ions).
4. Write name of series of hydrogen spectrum obtained when an electron transits from higher energy level to ground energy level .

Nuclei

1. A radioactive nucleus ‘D’ is decaying in the following way :

      

   Determine the atomic number and mass number of .
2. Write the function of coolant used in nuclear reactor.
3. Write the Rutherford-Soddy law of radioactive decay and derive a related equation. Draw the exponential decay curve of a radioactive substance. Write the ratio of half-life and mean life of a radioactive substance.

Semiconductor and Electronic Devices

1. What is amplification ? Draw a circuit diagram of NPN transistor as a common emitter amplifier. Write its working also.
2. What is P-N junction diode ? Draw a circuit diagram of the zener diode as a voltage regulator (voltage stabilizer). Write its working also.
3. What is intrinsic semiconductor and extrinsic semiconductor ? Write an example of each semiconductor.
4. Draw symbolic diagram of XOR gate.
5. Describe the experimental setup for obtaining the output characteristic curve of a PNP transistor in a common emitter configuration with a suitable circuit diagram. Also, draw the curve obtained.
6. Select the possible value of the common base current amplification factor of a transistor among the following. 0.9, 9, 19, 49 and 99
7. (a) Select acceptor type impurity among the following: arsenic (As), Antimony (Sb), gallium (Ga), and phosphorous (P). (b) Draw symbol of Zener diode.

Communication system

1. The maximum and minimum amplitude for an amplitude modulated wave are 10 V and 2 V respectively. Calculate the modulation index.
2. Draw block diagram of a communication system.
3. Define modulation.