Class Test - 1
Physics
TIME : 30 Min
Topic : Electrostatics
Date : 21/5/2022
Marks : 20
Section A : MCQ
Q1. The SI unit of electric flux is
10 x 1 = 10
(a) N C-1 m-2
(b) N C m-2
(c) N C-2 m2
(d) N C-1 m2
Q2. A charge Q is placed at the centre of the line joining two point charges +q and +q
such that they are in equilibrium . The ratio of charges Q and q is
(a) 1/4
(b) 4
(c) -1/4
(d) -4
Q3. SI unit of permittivity of free space is
(a) Farad
(b) Weber
(c) C2N-1 m-2
(d) C2N-1 m-2
Q4. Which of the following is not a property of field lines?
(a) Field lines are continuous curves without any breaks
(b) Two field lines cannot cross each other
(c) Field lines start at positive charges and end at negative charges
(d) They form closed loops
Q5.
Q6.
Q7.
Q8.
Q9. Three charges +4q, Q and q are placed in a straight line of length l at points at
distance 0, l/2, and l respectively. What should be Q in order to make the net force
on q to be zero?
(a) –q
(b) –2q
(c) –q/2
(d) 4q
Q10. Two point charges A and B, having charges +q and –q respectively, are
placed at certain distance apart and force acting between them is F. If 25% charge
of A is transferred to B, then force between the charges becomes:
(a) F
(b) 9F/16
(c) 16F/3
(d) 4F/3
Section B : Numerical (Any one)
Q11.
1x5=5
Q12. Two point charges of + 5 × 10–19 C and +20 × 10–19 C are separated by a
distance of 2 m. Find the point on the line joining them at which electric field
intensity is zero.
Section C : Derivation (Any one)
1x5=5
Q13. Using Gauss’s law obtain the expression for the electric field due to a
uniformly charged thin spherical shell of radius R at a point outside the shell.
Draw a graph showing the variation of electric field with r, for r > R and r < R.
Q14. (i) Define torque acting on a dipole of dipole moment p placed in a uniform
electric field E . Express it in the vector form and point out the direction along
which it acts.
(ii) What happens if the field is non-uniform?
(iii) What would happen if the external field E is increasing (i) parallel to p and (ii)
antiparallel to p ?