Class XII

Important Question

Electric Charge & Field

1. Four equal changes & are placed at the four corners A,B, C, D of a square of length Calculate the force on charge at B.

2. Write three properties of electric field lines.

3. S, and s₂ are two hollow Concentric spheres enclosing charge q and 2q respectively as shown in fig.

What is the ratio of electric flux through s, and s₂ ?

4. Derive an expression of electric field due to a dipole at point on the axis 

5. Define linear charge density 

6. A spherical Gaussian surface encloses a charge of 8.85X10-10 C

a. Calculate the electric flux passing through the surface

 b.How would the flux change if the radius of the Gaussian surface is doubled and why?

7. An infinitely long wire has linear charge density ‘¥’. An electron is revolving in a circle around it with uniform speed ‘v’. Find

• The kinetic energy of electron 

• Draw the graph between KE vs ¥.

8. Draw a graph to show the variation of E with distance r for the line of charge.

9. Two fixed point charge +4e and +e are separated by a distance ‘a’. Where should be third charge be placed for it to be in equilibrium.

10. Plot the graph between Electric Field (E) and distance ‘r’ for a uniformly charged plane sheet.

11. Electric Field inside a conductor is zero. Why?

12. If F1 and F2 be the forces between the two charges when they are kept in free space and a medium of dielectric constant k, respectively. Then find the value of F1:F2.