Physics – Important Question Bank for CBSE Class XII (HSC) Board Exam 2020

PHYSICS – IMPORTANT QUESTION BANK 2020

1. When is transistor said to be in active state? Draw a circuit diagram of a p-n-p transistor and explain how it works as a transistor amplifier. What will be the effect on anode current when (i) the intensity of light is potential is increased? (ii)In each case, all factors remain the same. Give justification to your answer.
2. What are the properties of Electric charge?
3. Draw and label diagram of a reflecting type of telescope over refracting type of telescope.
4. Name the shortest wavelength present in the Paschen series of spectrum line?
5. What is Faraday’s Law of Induction?
6. Write the Kirchhoff’s rules used in electric network. How are the rules justified?
7. With the help of the diagram explain the working of half wave rectifier and draw the input and output waveform.
8. Show does the force between two point charges change if the dielectric constant of the medium in which they are kept increase?
9. The distance of the field point on the equatorial plane of a small electric dipole is halved. By what factor will the electric filed due to the dipole change?
10. Explain briefly semiconductor. What are the types of semiconductor?
11. What is the difference between ‘Digital’ and ‘Analog’ form of communication.
12. State three important factors showing the need for translating a low frequency signal into a high frequency wave before transmission.
13. Calculate the magnetic field at the coil’s center if the radius and current flowing in a circular coil of wire having 200 turns are 20 cm and 2 A respectively.

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14. Explain the principle of Wheat Stone’s. Deduce using Kirchoff’s laws.
15. What is Biot-Savart law? Deduce the expression for the magnetic field at the point on the axis of a current carrying circular loop of a radius ‘R’ distant ‘X’ from the centre. Hence, write the magnetic field at the centre of a loop.
16. Show mathematically that the potential at a point on the equatorial line of an electric dipole is Zero?
17. Describe Hertz and Lenard’s experiment to demonstrate photoelectric effect.
18. Explain how the law of conservation of charge works on this phenomenon when charges appear on both the silk cloth and the glass rod when they are rubbed together.
19. Explain Ohm’s law briefly. What is the drawback of Ohm’s law?
20. Calculate the maximum current if the emf of a storage battery of a car is 25 V and the battery’s internal resistance is 1 Ω
21. Explain Ampere’s Circuital law briefly.
22. Check the order of magnitude of the earth’s field if the dipole of the magnetic moment is 20 × 10²²J T–1 and is located at its center.
23. If the length of the long metallic rod is 3.0 m and is rotated with an angular frequency of 700 radius–1 about an axis normal to the rod passing through its one end. Calculate the emf developed between the center and the ring. A circular metallic ring is in contact with the other end of the rod. A constant and uniform magnetic field of 0.10 T parallel to the axis exists everywhere.
24. If C₁=3_pF and C₂=2_pF, calculate the equivalent capacitance of the given network between A & B.
25. Explain with the help of the diagram, how depletion region and potential barrier are formed in a junction diode.
26. Explain how Magnetic Material is classified. Explain the components of Earth’s Magnetic field.
27. Explain schematically the equipotential surfaces corresponding to a constant electric field in z direction. A single positive charge at the origin.
28. Find out the direction and magnitude at a point 6 m east of the wire in which the current of 70 A is flowing and is passing in the north and south direction.
29. Keeping the voltage of the charging source constant. What would be the percentage change in the energy stored in a parallel plate capacitor if the separation between its plates were to decreased by 10%?
30. Explain the colour coding of carbon dioxide.

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31. What is the RMS voltage if the peak voltage of an Ac supply is 600V? What is the peak current if the RMS value of current in an Ac circuit 40A?
32. What is Magnetic Flux?
33. Explain Eddy current.
34. Three capacitor of capacitance 2pF, 3pF and 4pF are connected in parallel. What is the total capacitance of the combination? Determine the charge on each capacitor of the combination is connected to a 100V supply.
35. What can you say about the directions of its electric and magnetic field vectors of a plane electromagnetic wave t which is traveling in vacuum along z-direction and the frequency of the wave is 50 MHz and find out what is its wavelength?
36. Explain atoms. What is the line spectrum of the hydrogen atom?
37. What are the factors affecting photoelectric current?
38. A small sphere of radius r₁ and charge q₁ is enclosed by a spherical shell of radius r₂ and charge q₂. Show that if q₁ is positive, charge will flow from the sphere to the shell (when 2 wired are connected by a wire) no matter what the charge q₂ on the shell is.
39. In young’s double slit experiment, deduce the conditions for obtaining constructive and destructive interference fringes. Hence, deduce the expression for the fringe width. What should be the width of each slit to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern, for green light of wavelength 500nm, if the separation between two slit is 1mm?
40. What is total energy of an electromagnetic wave?
41. The angular width of a fringe is 0.5° on a screen which is positioned 2 m away in a double-slit experiment. The wavelength of the used light 500 nm. Find out the angular width of the fringe when the entire setup is under water. Assume refractive index to be 5/4?

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42. Write the properties of waves.
43. State Coulomb’s law and express it in vector form. Derive using Gauss theorem.
44. Derive an expression for conductivity in terms of mobility.
45. Explain amplitude modulation and illustrate it using diagram.
46. Discuss the principle construction theory and working of a transformer.
47. What is dispersion of light? What are its causes?