# KVPY Interview Important Questions Physics Part 2

Q: 11. Prove the law of conservation of energy

Sol. According to work energy theorem

In absence of external agent and non-conservative, force the total mechanical energy of a system remain constant.

Q: 12. What would happen to the people on the earth if it suddenly stopped rotating?

Sol. Their weight is increase

Q: 13. Why is a diode more efficient than a bulb?

Sol. Bulb consume more power then a diode

Q: 14. Write down the Faraday’s law of electromagnetic induction?

Sol. (i) When magnetic flux passing through a loop changes with time or magnetic lines of force are cut by a conducting wire then an emf is produced in the loop or in that wire. This emf is called induced emf. If the circuit is closed then the current will be called induced current

Magnetic flux

(ii) The magnitude of induced e mf is equal to the rate of change of flux w.r.t. time in case of loop. In case of a wire it is equal to the rate at which magnetic lines of force are cut by a wire

sign indicates that the e mf will be induced in such a way that it will oppose the change of flux. unit of magnetic flux = Weber.

Q: 15. Draw diagram of solenoid along with its magnetic field lines?

Sol.

Q: 16. Why does electric monopole exist while magnetic monopole does not exist?

Sol. Because magnetic dipole produce only due to current in a circular loops (due to revolution of electron around the nucleus). Magnetic lines of forces exists in a close loop only while electric lines of forces may be without a close loop

So magnetic monopole non exist

Q: 17. Derive the formula or relation

Sol. When a charge q moves with velocity in a magnetic field then the magnetic force experienced by moving charge is given by following formula:

Q: 18. Two parallel wires are kept carrying current in the same direction. Tell the type of force acting between them i.e. attraction/repulsion?

Sol. The magnetic force no charge between them, and force is force of attraction

Q: 19. Explain the meaning of resistive force. How will you write a resistive force in an equation?

Sol. It is a non conservative force which oppose the motion of object

Q: 20. Derive the velocity – time relationship for a body moving upwards against gravity and experiencing a resistive force

Sol.

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