**1.**An attractive force of 5N is acting between two charges of 2μc and -2μc placed at some distance. If the charges are mutuall touched and placed again at the same distance, what will be the new force between them.

**Zero**

**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)**

^{1/2}r**3.**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 twocharges?

**Q**

_{1}= 15 μc and Q_{2}= 5 μc.**4.**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**

**5.**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**

**6.**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?

**F**

_{1}= -4 N.**7.**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.

**q**

_{1}= 8 X 10^{-6}C and q_{2}= -2 X 10^{-6}C**8.**Two point charges, q =8×10

^{-8}C and Q= -2×10

^{-8}C are separated by a distance of 10 cm in air. What is the net electric field at the mid- point between the charges.

**Using the formulae=F/Q =3.6x**

**10**

^{5 }**9.**Two point charges 4 Q, Q are separated by 1 m in air. At what point on the line joining the charges is the electric field intensity zero?

**x=2/3 m**

**10 .**Two point charges of 16μC and -9μC are placed 8cm apart in air. Determine the position of the point at which resultant electric field is zero.

**11 .**Eight identical point charges of q Coulomb each are placed at corners of a cube of each side 0.1m .Calculate electric field at

the center of the cube. Calculate the field at the center when one of the corner charges is removed.

**i) zero ii) E = (1.2 x 10**

^{12})q N/C**12.**If the radius of the Gaussian surface enclosing a charge is halved, how does the electric flux through the Gaussian surface change?

**No change**

**13.**A charge Q micro coulomb is placed at the centre of a cube. What would be the flux through one face?

**Q/6ε**

_{0}**14.**The electric field in a certain region of space is (5i+4j-4k) x 10

^{5}N/C. Calculate the electric flux due to this field over an area of (2i-j) x 10

^{-2}m

^{2}

**ɸ**

**=E.S = 6 x 10**

^{3}Nm^{2}C^{-1}**15.**A sphere of radius 0.03m has a point charge of q = 7.6μC is located at its center. Find the electric flux

through it

**Φ=q/****ɛ****0 = 8.6 x 10**^{5}Nm^{2}C^{-1}**16.**A point charge of 17.7μC is located at the centre of a cube of side 0.03m. Find the electric flux through each face of the cube.

**1/6φ=1/6q/**

**ɛ**

**0 = 3.3 x 10**

^{5}Nm^{2}C^{-}^{1}

**17.**5,000 lines of force enter a certain volume of space and three thousands lines emerged from it. What is the total charge in Coulomb within the volume?

**-1.77 x 10**

^{-8}C**18.**A spherical Gaussian surface encloses a charge of 8.85 x 10

^{-8}C

i. Calculate the electric flux passing through the surface

ii. If the radius of the Gaussian surface is doubled, how would the flux change?

**i)10**

^{4}Nm^{2}C-1 ii) 10^{4}Nm^{2}C^{-1}