## Random collection of Physics Viva Questions

1. State the Principle of a potentiometer. (The students say that potential drop is proportional to length but the constant quantities are not mentioned)
2. How can we increase the sensitivity of a potentiometer?
3. Define figure of merit of a galvanometer.
4. Which has more resistance – a galvanometer or a milliammeter?
5. How does an LED emit light?
6. What is the difference between an ordinary diode and an LED?
7. Define principal axis of a convex lens?
8. What happens to the focal length of a concave mirror if it is immersed in water?
9. What are the factors affecting the internal resistance of a cell?
10. What are the difference between primary and secondary cell?
11. Why can’t we use a dry cell for starting a car?
12. What happens to the resistivity of a wire when it is doublefolded?
13. How does the resistance of a wire depend on its dimensions?
14. Why are the resistances used in a resistance box is like 1,2,2,5,10,20,20,50,100,200,200,500,1000,2000,2000,5000 etc?
15. Why constantan or manganin wires are used for making the resistance coils in resistance box?
16. What is a standard resistance?
17. What are the characteristics of a standard resistance?
18. What are the precautions to be observed while doing electricity experiments in general?
19. What is a galvanometer?
20. What is the resistance of an ideal ammeter?
21. Why is ammeter always connected in series and voltmeter always connected in parallel?
22. How can we convert a galvanometer into an ammeter or a voltmeter?
23. What is shunt?
24. What is AVO meter?
25. What is the effect of temperature on the resistance of a conductor?
26. Why does the resistance of a conductor increases with temperature, whereas that of a semiconductor decreases with temperature.
27. What is conductance?
28. What are non ohmic devices? give an example.
29. What are superconductors?
30. Define emf
31. Why emf is said to be a misnomer?
32. What happens if the battery used in the primary circuit of a potentiometer has less emf compared to the emf of the cell used in the secondary circuit?
33. If you find that the galvanometer reading is shaky, what error can you expect?
34. What do you mean by figure of merit of a galvanometer?
35. Why a moving coil galvanometer is called so?
36. What is the principle of a galvanometer?

## Numerical Problems From Optics

1. When an object of height 4cm is placed at 40cm from a mirror the mirror forms the image on the object itself. If the height of the image is equal to the height of the object. Find out the focal length of the mirror and identify the mirror.
2. A convergent beam of light passes through a diverging lens of focal length 0.2m and comes to focus at distance 0.3m behind the lens.Find the position of the point at which the beam would converge in the absence of lens?

## Kinetic Energy – Numerical Problem

a running man has half the kinetic energy that a boy of half his mass has.the man speed up by 1m/s and then has the same kinetic energy as the body. what were the original speeds of man and boy?

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## Numerical problem from image formation by spherical mirror – optics

An object is placed 18cm in front of a spherical mirror. if the image formed is 4cm to the right of the mirror calculate the focal length and radius of curvature? what is the nature of the mirror?

(The question was posted by Anisha)

## A Numerical Problem – Kinamatics

A particle is thrown vertically upward with a velocity of 19.6 m/s. Find (a) the acceleration of the particle at the highest point. (b) How high the particle will rise? (c) Time taken for rising to highest point.

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## A Numerical Problem from Kinematics

A car starts motion from rest at uniform acceleration of 2m/sec 2 for 3 seconds, and then it maintains a constant speed for 2 seconds.Then the breaks are used to decelerate the car uniformly to rest during a time of 3 seconds.

Draw the graph representing the journey of the car then calculate

1)the maximum speed in km/sec
2)the total displacement covered

(Ahmed sent this problem)

## CBSE 12th Std Physics Numerical from Optics

A convex lens of crown glass(1.5) has a focal length of 15 cm. The lens is placed in (a) water(1.33) and carbon bisulphide(1,65).determine in each case whether the lens behaves as a conveging or a diverging lens and determine its focal length.