Sunday, 20 March 2016


1.An attractive force of 5N is acting between two charges of 2μc and -2μc placed at some distance. If the charges are mutually touched and placed again at the same distance, what will be the new force between them.
2. Force of attraction between two charges at a distance d is F. What distance part should they kept in the medium so that force between them is F/3.
New distance = (3)1/2r
3. The force between two point charges kept at a distance d apart in air is F. If these charges are kept at same distance in water, how does the force between them is affected?
4 A metal sphere is held fixed on a smooth horizontal insulated plate and another metal sphere is placed at some distance away. If the fixed sphere is given a charge, how will the other sphere react?
When fixed sphere is given a charge it induces opposite charges on the nearer end and same kind of charges on the farther end of the other sphere. Now the net force between the two spheres is attractive in nature because unlike charges on both spheres are closer than the like charges on both spheres. So other sphere will be attracted towards the fixed sphere.
5. Two point charges q1 and q2 are 3 m apart and their combined charge is 20 μc. If one repels the other with a force of 0.075 N, what are two charges?
Q 1= 15 μc and Q2 = 5 μc.
6 A charge P repels charge Q but it attracts charge R. If R repels positively charged Body S, then find nature of charge on Q.
Q is negative
7. The force of attraction between two point charges placed at distance d apart in a medium is F. What should be the distance apart in the same medium so that the force of attraction between them becomes F/4?
New distance=2d
8 Two point charges of 2 μC and 6 μC repel each other with a force of 12 N. If each is now given additional charge of -4 μc, find new force?
F1 = -4 N.

9. Two point charges repel each other with a force of 100 N. One of these charges is increased by 10% and other is reduced by 10%.Find the new force of repulsion between them if distance is kept same.


10. The sum of two point charges is 6µc. They attract each other with a force of 0.9 N. When kept 40 cm apart in vacuum. Find their charges.
q1= 8 X 10 -6 C and q2 = -2 X 10 -6 C

11. Two identical charges Q each, kept at a distance r from each other. A third charge q is placed on the line joining the above two charges such that all the three charges are in equilibrium. What is the magnitude, Sign and position of the charge q?

q =Q ( x = r /2 )