Download 21. If an electric field is given by 10i + 3j + 4k calculate the electric

Electric Charge and Electric Field (Physics Paathshala)
14. Two charges of +25 x 10-9 coulomb and -25 x 10-9
coulomb are placed 6 m apart. Find the electric field
intensity ratio at points 4 m from the centre of the
electric dipole (i) on axial line (ii) on equatorial line
(1) 1000/49 (2) 49/1000 (3) 500/49 (4) 49/500
15. The electric force on a point charge situated on the
axis of a short dipole is F. If the charge is shifted along
the axis to double the distance, the electric force acting
will be (1) 4F
(2) F/2
(3) F/4
(4)F/8
22. Two isolated spheres of radii 2 cm and 4 cm
are given equal charge, then the ratio of charge
density on the surfaces of the spheres will be
(1) 1:2
(2) 4:1
(3) 8:1
(4) 1:4
23. Two long thin charged rods with charge
density  each are placed parallel to each other at
a distance d apart. The force per unit length
exerted on one rod by the other will be
16. A short dipole is placed along x-axis with centre at
origin. The electric field at a point P, which is at a
distance r from origin such that OP makes angle 45o
with x-axis, is directed along a direction
making
24. An electron is rotating around an infinite
positive linear charge in a circle of radius 0.1 m, if
the linear charge density is 1c/m then the velocity
of electron in m/s will be
(1) 0.562 x 107
(2) 5.62 x 107
7
(3) 562 x 10
(4) 0.0562 x 107
(1)
(2)
(3)
(4)
25. The electric field intensity at P and Q, in the
shown arrangement, are in the ratio
17. An electric dipole when placed in a uniform
electric field E will have minimum potential energy,
when the angle made by dipole moment with field E is
(1) 
(2) 3
(3) zero
(4) 

An electric dipole is placed at an angle 60° with
an electric field of strength 4 x 105 N/C. It
experiences a torque equal to 8√3 Nm. Calculate the
charge on the dipole, if dipole is of length 4cm
(1) 10-1 C
(2) 10-2 C
(3) 10-3 C
(4) 10-4 C
19. An electric dipole is placed in non-uniform
electric field. It may experience
(1) Resultant force and couple
(2) Only resultant force
(3) Only couple (4) All of these
20. A rectangular surface of sides 10 cm and 15 cm is
placed inside a uniform electric field of 25 V/m, such
that the surface makes an angle of 30° with the
direction of electric field. Find the flux of the electric
field through the rectangular surface
(1) 0.1675 N/m2C
(2) 0.1875 Nm2/C
(3) Zero
(4) 0.1075 Nm2/ C
21. If an electric field is given by 10i + 3j + 4k
calculate the electric flux through a surface of area 10
units lying in yz plane
(1) 100 units (2) 10 units (3) 30 units (4) 40 units
Q
26. The electric field in a region is radially
outward and at a point is given by E = 250r V/m
(where r is distance of the point from origin).
Calculate the charge contained in a sphere of
radius 20 cm centred at the origin
(1) 2.22 x 10-6 C
(2) 2.22 x 10-8 C
(3) 2.22 x 10-10 C
(4) Zero
27. A: If dipole moment of water molecules were
zero then microwave cooking would not be
possible.
R:In a microwave oven water molecules vibrate
due to oscillating electric field in microwave
heat the food.
28.A:When an electric dipole is placed in
uniform electric field, net force on it will be
zero.
R:Force on the constituent charges of the dipole
will be equal and opposite when it is in uniform
electric field.
29. A: Gauss' theorem is applicable on any closed
surface.
R: In order to find the value of electric field due
charge distribution, Gauss' theorem should
applied on a symmetrical closed surface.
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