### Most important questions Class 12 NEB Physics 2078

Wave and Optics
1. Define wave motion. Derive the progressive wave equations in a medium.
2. Starting with the definition of stationary waves, prove that the distance between any two consecutive nodes or antinodes in a stationary wave is λ/2.
3. Write an expression for Newton's formula for the velocity of sound in air. Explain the necessary correction made by Laplace.
4. Define end correction. Show that, in an open organ pipe, both odd and even harmonics can be produced.
5. Define natural frequency. Describe an experiment to determine the velocity of sound in air by the resonance air column tube method.
6. Describe sound waves as pressure waves and deduce an expression for the pressure amplitude.
7. Define beats. Obtain an expression for the beat frequency produced by the superposition of two waves of slightly different frequencies.
8. What is the Doppler effect in sound? Obtain an expression for the apparent frequency of sound when both source and observer are moving towards each other.
9. State Huygen's law and use it to verify Snell's law.
10. Describe Michelson's method to determine the velocity of light.
11. Define coherent sources of light. Describe Young's double-slit experiment and show that the bright fringes and dark fringes are equally spaced.
12. Define polarization of light. Show that, μ=tanθp where the symbols have their usual meanings.

13. Electricity and Magnetism
14. How can you convert a galvanometer into an ammeter (or voltmeter)? Explain.
15. Discuss the mechanism of metallic conduction. Derive a relation between current density and drift velocity. i.e, I=ηeΑνd
16. State and apply Kirchoff's rule to measure the unknown resistance of a wire by using the Wheatstone bridge circuit.
17. State the principle of meter bridge. Describe how it is used to determine the resistance of a wire.
18. What is the principle of a potentiometer? Explain with necessary theory how you would determine the internal resistance of a cell using this principle.
19. What do you mean by the thermoelectric effect? Discuss the variation of thermo emf in a thermocouple with the change in temperature.
20. State and explain Biot - Savart's law. Use it to find the magnetic field due to a long straight current-carrying conductor.
21. State Ampere's law. Deduce an expression for the force between two parallel current-carrying wires.
22. State Faraday's law of electromagnetic induction. Derive an expression for the emf induced in a straight conductor moving at right angles to the direction of a uniform magnetic field.
23. State Faraday's law of electromagnetic induction. Deduce an expression for the emf induced in a coil rotating uniformly in a uniform magnetic field.
24. Explain the principle and working of a transformer.
25. Discuss the condition for the resonant frequency of the LCR alternating current circuit.

26. Modern Physics
27. Describe the construction and working principle of Millikan's oil-drop experiment to determine the charge of an electron.
28. Define cross-field. Describe the construction and working principle of J.J. Thomson's experiment to determine the specific charge of an electron.
29. Define threshold frequency and work function of a metal. Explain Einstein's photoelectric equation.
30. Describe the experiment to determine Planck's constant.
31. State Bohr's postulates for the atomic model. Derive the expression for the radius of an electron bound to a hydrogen atom. (OR, to find the total energy of an electron in nth orbit.)
32. Describe the working of He - Ne laser.
33. Explain Bragg's law of diffraction for X - rays.
34. What is Zener's breakdown? How can a Zener diode be used as a voltage regulator? Explain.
35. Define mass defect. Explain the significance of the graph of binding energy per nucleon versus the atomic mass number.
36. State the laws of radioactivity. Derive the relation between half-life period and decay constant.