School of Physics
University of Hyderabad
End Semester Examination
Electromagnetic Theory โ I (PH403)
Date: 20/2/2021 Total Marks: 40 Time: 2.15 hour
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(Question 1-10 , carry 1 mark each)
1. Three charged particles are placed on a straight line as shown in figure. q 1 and q2
are fixed but q3 can be moved under the action of the forces from q1 and q2 . if q3
is in equilibrium then what is the relation between q1 and q2?
(a) q1 = 4q2 (b) q1 = -q2 (c) q1 = -4q2 (d) q1 = q2
2. An isolated charge q1 of mass m is suspended freely by a thread of length l. And
another charge q2 is placed at a distance r from q1. when q1 is in equilibrium, the
tension in thread will be
(a) mg (b) > mg (c) < mg (d) none of the above
3. Two free charges q and 4q are at a distance l apart. To bring the system in
equilibrium magnitude and sign of the third charge will be
(a) Q = โ 4
9 q (b) Q = 4
9 q (c) Q = 3
5 q (d) Q = โ 3
5 q
4. S1 and S2 are two parallel concentric spherical surfaces enclosing charges q and
2q respectively. Then the ratio of the electric flux
through S1 and S2 is
(a) 1/2 (b) 1/3 (c) 2 (d) 3
5. Gauss law of electrostatics states that Electric flux โฎ๐ธ. ๐๐
๐ = ๐
๐0
Statement 1 : the electric field E is due to all the charges both inside and outside
the surface S
q2
q1
l
r
