# Class 12 Physics : Important Questions and Topics for NEB exam.

## 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 ƛ/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 a sound wave as a pressure wave 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.

## Electricity and Magnetism

1. How can you convert a galvanometer into an ammeter (or voltmeter)? Explain.
2. Discuss the mechanism of metallic conduction. Derive a relation between current density and drift velocity.
3. State and apply Kirchoff's rule to measure the unknown resistance of a wire by using the Wheatstone bridge circuit.
4. State the principle of meter bridge. Describe how it is used to determine the resistance of a wire.
5. What is the principle of a potentiometer? Explain with necessary theory how you would determine the internal resistance of a cell using this principle.
6. What do you mean by the thermoelectric effect? Discuss the variation of thermo emf in a thermocouple with the change in temperature.
7. State and explain Biot - Savart's law. Use it to find the magnetic field due to a long straight current-carrying conductor.
8. State Ampere's law. Deduce an expression for the force between two parallel current-carrying wires.
9. 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.
10. State Faraday's law of electromagnetic induction. Deduce an expression for the emf induced in a coil rotating uniformly in a uniform magnetic field.
11. Explain the principle and working of a transformer.
12. Discuss the condition for the resonant frequency of the LCR alternating current circuit.

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