#### 12th Standard English Medium Physics Reduced syllabus Three mark important Questions with Answer key - 2021(Public Exam )

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 75

3  Marks

25 x 3 = 75
1. Calculate the electrostatic force and gravitational force between the proton and the electron in a hydrogen atom. They are separated by a distance of 5.3 x 10–11 m. The magnitude of charges on the electron and proton are 1.6 x 10–19 C. Mass of the electron is me = 9.1 x 10–31 kg and mass of proton is mp = 1.6 x 10–27 kg.

2. Consider the charge configuration as shown in the figure. Calculate the electric field at point A. If an electron is placed at points A, what is the acceleration experienced by this electron? (mass of the electron = 9.1 x 10-31 kg and charge of electron = −1.6 x 10-19 C)

3. A sample of HCl gas is placed in a uniform electric field of magnitude 3 x 104 NC-1. The dipole moment of each HCl molecule is 3.4 x 10-30 Cm. Calculate the maximum torque experienced by each HCl molecule.

4. Obtain the expression for energy stored in the parallel plate capacitor.

5. Explain in detail how charges are distributed in a conductor, and the principle behind the lightning conductor.

6. Define potential difference and derive.

7. A copper wire of cross-sectional area 0.5 mm2 carries a current of 0.2 A. If the free electron density of copper is 8.4 x 1028 m-3 then compute the drift velocity of free electrons.

8. Calculate the equivalent resistance in the following circuit and also find the values of current I, I1 and I2 in the given circuit.

9. Obtain the macroscopic form of Ohm’s law from its microscopic form and discuss its limitation.

10. Explain the determination of unknown resistance using meter bridge.

11. A short bar magnet has a magnetic moment of 0.5 J T–1. Calculate magnitude and direction of the magnetic field produced by the bar magnet which is kept at a distance of 0.1 m from the centre of the bar magnet along
(a) axial line of the bar magnet and
(b) normal bisector of the bar magnet.

12. Calculate the magnetic field at a point P which is perpendicular bisector to current carrying straight wire as shown in figure.

13. Magnetic field lines can be entirely confined within the core of toroid, but not within a straight solenoid. Why?

14. A circular loop of area 5 x 10–2 m2 rotates in a uniform magnetic field of 0.2T. If the loop rotates about its diameter which is perpendicular to the magnetic field as shown in figure. Find the magnetic flux linked with the loop when its plane is
(i) normal to the field
(ii) inclined 60o to the field and
(iii) parallel to the field.

15. The self-inductance of an air-core solenoid is 4.8 mH. If its core is replaced by iron core, then its self-inductance becomes 1.8 H. Find out the relative permeability of iron.

16. A circular metal of area 0.03 m2 rotates in a uniform magnetic field of 0.4 T. The axis of rotation passes through the centre and perpendicular to its plane and is also parallel to the field. If the disc completes 20 revolutions in one second and the resistance of the disc is 4 Ω, calculate the induced emf between the axis and the rim and induced current flowing in the disc.

17. Derive an expression for phase angle between the applied voltage and current in a series RLC circuit.

18. Compare the electromagnetic oscillations of LC circuit with the mechanical oscillations of blockspring system qualitatively to find the expression for angular frequency of LC oscillator.

19. Obtain lens maker’s formula and mention its significance.

20. Light travelling through transparent oil enters in to glass of refractive index 1.5. If the refractive index of glass with respect to the oil is 1.25, what is the refractive index of the oil?

21. A monochromatic light is incident on an equilateral prism at an angle 30o and emerges at an angle of 75o. What is the angle of deviation produced by the prism?

22. Discuss the spectral series of hydrogen atom.

23. Discuss the beta decay process with examples.

24. Obtain the equation for resolving power of optical instruments.

25. Find the current through the Zener diode when the load resistance is 2 kΩ. Use diode approximation.