Electricity and Magnetism Answers

17) A sphere of radius
a
is made of insulating material and has charge distributed uniformly throughout its volume. The charge density is
ρ
. Find the field due to the charge for
r≤a
.
a) rρ3ϵ0

b) 2rρϵ0

c) rρπϵ0

d) rρ3πϵ0
18) A galvanometer of resistance
120Ω
a full scale deflection with a current of 0.0005A. How would you convert it to an ammeter that reads a maximum current of 5A?
a) connect
2000Ω
in parallel to it
b) connect
200.12Ω
in series to it
c) connect
20.10Ω
in series to it
d) connect
0.012Ω
in parallel to it

16 Which of the following correctly gives the electric field at the centre of a uniformly charged semicircular arc of radius
a
and charge per unit length,
λ
?
a) λ2πϵ0a

b) 2λπϵ0a

c) λπϵ0a2

d) λπϵ0a
15) A uniform electric field of 200 N/C is in the x-direction. A point charge of
3μC
is released from rest at the origin. What is the kinetic energy of the charge when it is at x = 4 m?

a) 2.4×10−2J

b) 1.6×10−2J

c) 3.6×10−2J

d) 4.8×10−2J

13) Find the electric field at the point P due to the charges shown in the figure
Click here to see exhibit

a) 463×104N/C
at
24o

b) 46.1×104N/C
at
141o

c) 54×104N/C
at
117o

d) 411×104N/C
at
26o

14) The electric potential difference between two points A and B is 42 V. What is the work done by an external agent in carrying a charge of
5.0×10−5C
from A to B at constant speed?

a) 2.1×10−3J

b) 8.4×10−4J

c) 21×10−4J

d) 8.4×10−3J

12) Which of the following is NOT true about the electric field intensity
E⃗
E→
of a uniformly charged solid sphere?
a) E⃗
E→
is maximum at the surface of the sphere

b) E⃗
E→
is directly proportional to the distance from the centre of the sphere

c) E⃗
E→
decreases as a square of the distance from the surface of the sphere

d) E⃗
E→
decreases as a square of the distance from the centre of the sphere.

11) From Gauss’ law which of the following is NOT correct?
a) The outward flux of electric field through an enclosed surface is proportional to the electric charges enclosed
b) The field at a point outside a spherically symmetric charge is the same as the electric field at the same point due to a point charge at its centre.
c) The electric flux through a Gaussian surface is a vector product of the electric field and a unit vector perpendicular to and outward from the surface
d) The total electric flux through a cylinder placed in an electric field with its axis parallel to the field is zero

7) What are the dimensions of the constant k in Coulomb’s law of electrostatics?

a) ML2T−4T−2A−1

b) ML2T3A-2

c) M−2L3T2A−1

d) ML3T−4A−2

8) The two tiny balls shown in the figure have identical masses of 0.20 g each. When suspended from 50-m long string, they make an angle of
37o
to the vertical. If the charges on each ball are the same, how large is each charge?
Click here to see exhibit

a) 0.48μC

b) 0.36μC

c) 0.24μC

d) 0.62μC

5 )A tiny ball of mass 0.60 g is suspended from a rigid support with a piece of thread in a horizontal electric field of intensity 700 N/C. The ball is in equilibrium when the thread is inclined at an angle of
20o
to the vertical. What are the magnitude and sign of the charge on the ball? Take
g=9.8m/s2

a) −3.1×10−6C

b)3.2×10−6C

c)4.2×10−6C

d)−4.1×10−3

6) The following are true about electric field lines except that they
a) are drawn such that the magnitude of the field is proportional to the number of lines crossing a unit area perpendicular to the lines
b) do not intersect one another
c) are discontinuous and may terminate in a vacuum
d) give the direction of motion of a unit positive test-charge under the action of the electrostatic force

3) Which of the following is NOT correct?
a) Electric charge cannot be produced by frictional forces
b) Electric charge is conserved
c) Electric charges are integral multiple of the electronic charge
d) induced charges are the result of charge separation within a material

4) Which of the following is not true of an electrostatic force?
a) it acts along the line joining the point charges
b) it obeys an inverse square law
c) it is mutually attractive or repulsive
d) it is weaker than the gravitational attraction between the charged particles.

1)Which of the following fundamental forces forces of nature is responsible for the existence of bulk matter?
a) force of gravity
b) electromagnetic force
c) nuclear strong force
d)nuclear weak force

2) Two charges
Q1=500μC
Q1=500μC
and
Q2=100μC
Q2=100μC
are located on the XY plane at the positions
r1=3j⃗
r1=3j→
m and
r2=4i⃗
r2=4i→
m . Find the force exerted on the
Q2
Q2
a)
14.4i⃗ +10.8j⃗
14.4i→+10.8j→
N
b)
14.4i⃗ –10.8j⃗
14.4i→–10.8j→
N
c)
10.8i⃗ –14.4j⃗
10.8i→–14.4j→
N
d)
10.8i⃗ +14.4j⃗
10.8i→+14.4j→
N

what is the difference between "charge" and "ion"?