ASSIGNMENT 1 - XII (2025-26)
PHYSICS (042)
1) Coulomb force F versus (1/r2) graphs for two pairs of
point charges (q1 and q2) and (q2 and q3) are shown
in the figure. The ratio of charges (q1 /q3) is:
a) √3 b) 1 /√3 c) 3 d) 1/ 3
2) Electric field lines of a non-uniform electric field are
shown in the figure. According the figure:
a) EP > EQ > ER
b) EP = EQ = ER
c) EP = ER > EQ
d) EP = ER < EQ
3) Electric charge +q, +q and −2q are placed at the corners of an equilateral
triangle ABC of side l. The magnitude of electric dipole moment of the
system is
a) ql b) 2ql
c) √3 ql d) 4ql
4) A thin plastic rod is bent into a circular ring of radius R. It is uniformly
charged with charge density λ. The magnitude of the electric field at its
centre is:
a) λ /2𝜖0 R b) Zero
c) λ /4π𝜖0 R d) λ /4𝜖0 R
5) A negatively charged object X is repelled by another charged object Y.
However, an object Z is attracted to object Y. Which of the following is the
most possibility for the charge of object Z?
a) positively charged only
b) negatively charged only
c) neutral or positively charged
d) neutral or negatively charged
6) An electric dipole having a dipole moment of 4 × 10-9 C m is placed in a
uniform electric field such that the dipole is in stable equilibrium. If the
magnitude of the electric field is 3 × 103 N/C, what is the work done in
rotating the dipole to a position of unstable equilibrium?
a) zero b) 1.2 × 10-5 J
c) 2.4 × 10-5 J d) - 1.2 × 10-5 J
7) A square sheet of side 'a' is lying parallel to XY plane at z=a. The electric
field in the region is E=cz2 𝑘̂ . The electric flux through the sheet is
a) a4c b) a3c /3
c) a4c /3 d) 0
8) Two charges q1 and q2are placed at the centres of two spherical conducting
shells of radius 𝑟1 and 𝑟2 respectively. The shells are arranged such that their
centres are d [> (𝑟1+𝑟2)] distance apart. The force on q2 due to q1 is:
1 𝑞1 𝑞2 1 𝑞1 𝑞2
a) b)
4𝜋𝜖0 𝑑2 4𝜋𝜖0 (𝑑−𝑟1 )2
1 𝑞1 𝑞2
c) 𝑧𝑒𝑟𝑜 d)
4𝜋𝜖0 [𝑑−(𝑟1 +𝑟2 )]2
9) Two-point charges placed in a medium of dielectric constant 3 are at a
distance r between them and experience an electrostatic force ' F ', The
electrostatic force between them in a vacuum at the same distance ' r ' will
be
a) 3 F b) F
c) F/2 d) F/3
10) Which statement is true for Gauss law:
a) all the charges whether inside or outside the gaussian surface contribute
to the electric flux.
b) electric flux depends upon the geometry of the gaussian surface.
c) gauss theorem can be applied to non-uniform electric field.
d) the electric field over the gaussian surface remains continuous and
uniform at every point.
11) The sum of two-point charges is 7μC. They repel each other with a force
of 1 N when kept 30 cm apart in free space. Calculate the value of each
charge.
12) A particle of mass m carrying a charge − q1 starts moving around a fixed
charge + q2 along a circular path of radius r. Find the time period of
revolution T of charge − q1.
13) Electric charges of 1μC, −1μC and 2μC are placed in air at the corners A,
B and C respectively of an equilateral triangle ABC having length of each
side 10 cm. Find the resultant force on the charge at C.
14) Equal charges q are placed at the four corners A, B, C, D of a square of
length a. Find the magnitude of the force on the charge at B.
15) Two spherical conductors B and C having equal radii and carrying equal
charges in them repel each other with a force F when kept apart at some
distance. A third spherical conductor having same radius as that of B but
uncharged is brought in contact with B, then brought in contact with C and
finally removed away from both. Find the new force of repulsion between B
and C.
16) a) Consider three metal spherical shells A, B and C, each of radius R. Each
shell is having a concentric metal ball of radius R/10. The spherical shells A,
B and C are given charges +6q, −4q, and 14q respectively. Their inner metal
balls are also given charges −2q, +8q and −10q respectively. Compare the
magnitude of the electric fields due to shells A, B and C at a distance 3 R
from their centres.
b) A charge −6μC is placed at the centre B of a semicircle of radius 5 cm, as
shown in the figure. An equal and opposite charge is placed at point D at a
distance of 10 cm from B. A charge +5μC is moved from point ' C ' to point '
A ' along the circumference. Calculate the work done on the charge.
17) A small spherical shell S1 has point charges q1=−3μC, q2=−2μC and
q3 = 9μC inside it. This shell is enclosed by another big spherical shell S2. A
point charge Q is placed in between the two surfaces S1 and S2. If the
electric flux through the surface S2 is four times the flux through surface S1,
find charge Q.
18) A point charge causes an electric flux of -1000 Nm2/C to pass through a
spherical Gaussian surface of 10.0 cm radius centred on the charge. If the
radius of the Gaussian surface were doubled, how much flux would pass
through the surface? Also calculate the charge causing this flux.
19) A charge +q fixed on the Y axis at a distance of 1 m from the origin and
another charge +2q is fixed on the X axis at a distance of 2 m from the
origin. A third charge −q is placed at the origin. Find the direction in which
−q charge moves.
20) An electron moves a distance of 6.0 cm when accelerated from rest by
an electric field of strength 2× 104 N/C. Calculate the time of travel.
21) An infinitely long positively charged straight wire has a linear charge
density λ. An electron is revolving in a circle with a constant speed v such
that the wire passes through the centre and is perpendicular to the plane of
the circle. Find the kinetic energy of the electron in terms of magnitudes of
its charge and linear charge density λ on the wire. Draw a graph of kinetic
energy as a function of linear charge density λ.
22) If the radius of the Gaussian surface enclosing a charge is halved, how
does the electric flux through the Gaussian surface change?
23) A charge Q is placed at the centre of an imaginary hemispherical surface.
Using symmetry arguments and the Gauss's law, find the flux of the electric
field due to this charge through the surface of the hemisphere.
24) Two charges +10 𝜇𝐶 and +40 𝜇𝐶 are placed 12 cm apart in air. Find the
position where electric field intensity is zero.
25) Two charges, each of 5 μC but opposite in sign, are placed 4 cm apart.
Calculate the electric field intensity of a point that is a distance 4 cm from
the midpoint on the axial line of the dipole.
