RS ACADEMY Total Marks:20marks

Total Time: 0:30hr

Satellite, Chandkheda
STD : 11 and 12 (GSEB/CBSE)

Class -12th TEST -1.4

Answer the following MCQ (1×10 =10) 5. Two-point charges of q and 4q are kept 30 cm
1. Charges 2q and -q are placed at (a,0) and (-a,0) apart. At a distance…., on the straight line joining
as shown in the figure. The coordinates of the them, the intensity of electric field is zero.
point at which electric field intensity is zero (a) 20 cm from 4q (b) 7.5 cm from q
will be (x,0) , where x is (c) 15 cm from 4q (d) 5 cm from q
6. An electron of mass Me, initially at rest, moves
through a certain distance in a uniform electric
field in time t1. A proton of mass Mp, also initially
at rest, lakes time t2 to move through an equal
distance in this uniform electric field. Neglective
(a) -a < x < a (b)x<-a t2
(c)x>-a (d)0<x<a in the effect of gravity, the ratio is nearly
2. Five-point charges (+ q each) are placed at the t1
five vertices of a regular hexagon of side 2a. equal to .....
What is the magnitude of the net electric field Mp
at the centre of the hexagon? (a) 1 (b)
Me
1 q 1 q
(a) (b) Me
4 0 a 2 16 0 a 2 (c)
Mp
(d) 1836

1 2q 1 5q 7. An electron moving at a speed of 3  106 m / s

(c) (d)
4 0 a2 16 0 a 2 along negative X-axis in an electric field and stops
3. The variation of electric field between two after covering 90 mm distance. The intensity of
charges q1 and q 2 and along the line joining the this electric field is.......
charges is plotted against distance from q1 (e = 1.6 10−19 C, m e = 9.110 −31 kg)
(taking rightward direction of electric field as (a) 2.84 kVm–1, negative X direction
positive) as shown in the figure. Then, the (b) 0.284 kVm–1, negative X direction
correct statement is (c) 0.284 kVm–1, Positive X direction
(d) 28.4 kVm–1, Positive X direction
8. A charge +10 −9 C is located at the origin of a
Cartesian coordinate system and another charge Q
at (2, 0, 0) m. If X component of the electric field
at (3, 1, 1) m is zero, then Q = …
(a) −0.43  10 −9 C (b) 0.43  10 −9 C
(c) −0.46  10 −9 C (d) 0.46  10 −9 C
(a) q1 and q 2 are positive and q1 < q 2 9. A charged oil drop is suspended in a uniform field
(b) q1 and q 2 are positive and q1 > q 2 of 3 × 104 V/m so that it neither falls nor rises.
The charge on the drop will be (Take the mass of
(c) q1 is positive and q 2 is negative q1  q2 the charge = 9.9 × 10–15 kg and g = 10m/s2)
(a) l.6 × 10–18C (b) 3.2 × 10–18C
(d) q1 and q 2 is negative q1  q2 –18
(c) 3.3 × 10 C (d) 4.8 × 10–18C
4. When an electron and a proton are both placed 10. A positively charged ball hangs from a silk thread.
in an electric field…. We put a positive test charge q 0 at a point and
(a) the electric forces acting on them are equal
in magnitude as well as direction. measure F/q 0 , then it can be predicted that the
(b) only the magnitudes of force are same. electric field strength E will be
(c) accelerations produced in them are same. F F
(d) magnitudes of accelerations produced in (a) = (b) 
q0 q0
them are same.

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Physics RS Academy

F
(c)  (d) none of the above.
q0
Answer the following short questions (2×2=4)
11. Figure shows tracks of three charged particles
in a uniform electrostatic field. Give the signs
of the three charges. Which particle has
the highest charge to mass ratio?

12. Derive the expression of electric field due to

multiple charges.
Answer the following long questions (3×2=6)
13. Two-point charges q1 and q2, of magnitude
+10–8 C and –10–8 C, respectively, are
placed 0.1 m apart. Calculate the electric
fields at points A, B and C shown in Fig.

14. Two-point charges qA = 3 μC and qB = –3 μC

are located 20 cm apart in vacuum.
(a) What is the electric field at the midpoint O of
the line AB joining the two charges?
(b) If a negative test charge of magnitude 1.5 ×
10–9 C is placed at this point, what is the
force experienced by the test charge?

Ronak Shah - 9428239499 Page 2 of 2

 RS ACADEMY Total Marks:20marks
Total Time: 0:30hr
Satellite, Chandkheda
STD : 11 and 12 (GSEB/CBSE)

Class -12th TEST -1.5

Answer the following MCQ (1×10 =10) (c) Dipole moves along positive x-axis after
1. If the magnitude of intensity of electric field at under going an anticlockwise rotation
a distance x on axial line and at a distance y on (d) Dipole moves along negative x-axis and
equatorial line on a given dipole are equal, undergoes an anticlockwise rotation
then x : y is 5. An electric dipole of length l has dipole moment p
(a)1 : 1 (b) 1: 2 is bent in the form of a half circle. Its new dipole
(c)1 : 2 (d) 3
2 :1 moment will be .....
2. Three charges of (+2q), (– q) and (– q) are p 2p
(a) (b)
placed at the corners A, B and C of an 2 
equilateral triangle of side a as shown in the p
adjoining figure. Then the dipole moment of (c) (d) 2p
this combination is 2
6. An electric dipole consists of two opposite
+2q charges each 0.05 separated by 30 mm. The
A dipole is placed in an uniform external electric
a
field of The maximum torque exerted
a
by the field on the dipole is
1) 2)
B C 3) 4)
–q a –q 7. An electric dipole consists of two opposite
charges of magnitude 10−6 C separated by 100 Å.
(a) qa (b)Zero The intensity of electric field at a distance 10 cm
2 from its midpoint on its equator is ......
(c) qa 3 (d) qa
3 (a) 9 NC −1 (b) 0.9 NC −1
3. An electric dipole in a uniform electric field (c) 90 NC −1 (d) 0.09 NC−1
experience →
(a) Force and torque both 8. An electric dipole of moment p is placed in a
(b) Force but no torque
uniform electric field E. The dipole is rotated
(c) Torque but no force
through a very small angle θ from equilibrium and
(d) No force and no torque
is released. If I is the moment of inertia of the
4. There exists a non-uniform electric field along dipole then it will execute simple harmonic
x-axis as shown in figure. The field increases oscillations with frequency ..........
at a uniform rate along positive x-axis. A
1 pE p E
dipole is placed inside the field as shown. For (a) ƒ = (b) ƒ =
the dipole which one of the following 2 I 2 I
statement is correct 1 I p I
(c) ƒ = (d) ƒ =
2 pE 2 E
9. Two electric dipoles of moment p and 64 p are
–q placed in opposite direction on a line at a distance
+q
X-axis of 25 cm. The electric field will be zero at point
between the dipoles whose distance from the
dipole of moment p is
25
a)5 cm b) cm
(a) Dipole moves along positive x-axis and 9
undergoes a clockwise rotation 4
c)10 cm d) cm
(b) Dipole moves along negative x-axis after 13
undergoing a clockwise rotation 10. The electric field at a point on equatorial line of a
dipole and direction of the dipole moment
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Physics RS Academy

a) will be parallel
b) will be in opposite direction
c) will be perpendicular
d) are not related
Answer the following short questions (2×2=4)
11. A system has two charges qA = 2.5 × 10–7 C
and qB = –2.5 × 10–7 C located at points A:
(0, 0, –15 cm) and B: (0,0, +15 cm),
respectively. What is the total charge and
electric dipole moment of the system?
12. Derive the expression of torque acting on a
dipole kept in a uniform electric field.
Answer the following long questions (3×2=6)
13. Derive the expression of Electric Field due to
a dipole along its axial line.
14. Two charges ±10 μC are placed 5.0 mm apart.
Determine the electric field at (a) a point P on
the axis of the dipole 15 cm away from its
centre O on the side of the positive charge, as
shown in Fig. (a), and (b) a point Q, 15 cm
away from O on a line passing through O and
normal to the axis of the dipole, as shown in
Fig. (b).

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