IIth std
X REVESION TEST – 1
Time : 1Hr 45 minutes PHYSICS [ NCERT + NCERT EXEMPLER ] M.M : 50
TEST TOPIC :Electric Charges and Fields , Electrostatic Potential and Capacitance , Current Electricity .
PART-A .
1. (A)Show, on a plot, variation of resistivity as a function of temperature.
(i)a conductor (a) copper (b)nichrome(ii)a typical semiconductor (gallium arsenide)
(B) Using the expression for the resistivity in termsof number density and relaxation time between the collisions,
explain how resistivity in the case of a conductor increases while it decreases in a semiconductor, with the rise of
Temperature.
(C) Define the terms 'temperature coefficient of resistance' and 'electrical conductivity of a conductor.
Why are constantan and manganin used for making standard resistances? Explain.
2. T
wo conducting spheres of radius r1 = 8 cm and r2 = 2 cm are separated by a distance much larger than 8 cm and are
connected by a thin conducting wire as shown in thefig – 1. A total charge of Q = +100 nC is placed on one of the
spheres.After a fraction of a second, the charge Q is redistributed and both the spheres attain electrostatic equilibrium.
fig – 1
( i)Calculate the charge and surface charge density on each sphere.
(ii)Calculate the potential at the surface of each sphere.
3. ( A)Define DIELECTRICS AND POLARISATION .
(B)Explain the difference in behaviour of a conductor and a dielectric in an external electric field.
(C)Show thata dielectric develops a net dipole moment in an external electric field.
(a) Non-polar molecules, (b) Polar molecules. Using diagram
(D) Differentiate between (a) Non-polar molecules, (b) Polar molecules & give 2 example of each
(E)Write the relation between polarization of a dielectric with electric susceptibility.
PART-B .
4. A
conducting spherical shell of radius R has charge Q uniformly distributed on them. The centre of the sphere is at
x = 0 . Find the magnitude and direction of thenet electric field and potential on the X-axis at
𝑅
(i) x = 0 (ii) x = (iii) x = 3R . Plot relation between𝐸 Vs r. For given case
2
5. Find currents in different branches of the electric circuit shown infig – 2.
fig – 2
6. (A)Describe the behavior of a dipole when placed at different angles with respect to a uniform electric field
(i) θ = 0° (ii) θ = 90° (iii) θ = 180°
(B)An electric dipole of length 4 cm, when placedwith its axis making an angle of 60° with a uniform
electric field, experiences a torque of 4 3Nm. Calculate the potential energy of the dipole,
if it has charge ± 8 nC .
7. Find the expression for the capacitance of a parallel plate capacitor of plate area A and plate separation d when a
𝑑
𝑑
dielectric slab of thickness𝑡 = 4
& a metallic slab of thickness 𝑡 = 3
where (𝑡< d) are introduced one by
one between the plates of the capacitor. In which case would the capacitance be more and why?
PART-C .
8. F
ind the emf and internal resistance of a single battery which is equivalent to a combination of three batteries as
shown infig – 3.
fig – 3
9. O
hm's law is not a fundamental law of nature. State the conditions under which Ohm's law fails. Give one example
for each case.
10. Two charges q1 and q2 are placed at (0, 0, d) and (0, 0, –d) respectively. Find the locus of points where the potential
is zero.
11. The electric field in a region is given by 𝐸 = (10𝑥 + 4)𝑖
where𝑥is in meter and E is in N/C. Calculate the amount of work done in taking a unit charge from
(i) (5 m, 0) to (10 m, 0) (ii) (5 m, 0) to (5 m, 10 m)
12. Two charges 2µC and –2µC are placed at points A and B 6 cm apart.
(A) Identify an equipotential surface of the system.
(B)What is the direction of the electric field at every point on this surface?
13. Thefig – 4 shows electric potential V as a function ofx.
fig – 4
(i) Rank the four regions according to the magnitude of x- component of the electric field E
(ii)Plot electric field (E) as a function of x ,for the above figure .
PART-D .
Assertion-Reason Type Questions(14 - 16)
(A)Both Assertion (A) and Reason (R) are true but Reason (R) isNOTcorrect explanation of Assertion (A)
( B)Assertion (A) is true but Reason (R) is false
(C)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A)
(D)Assertion (A) is false and Reason (R) is true.
14. Assertion (A) : As per theFig – 5, a point charge +q is placed at origin O. Work done in taking another point
charge – Q from the point A (0, a) to another point B (a, 0) along the straight path AB is zero
Fig – 5
Reason (R) :Work done to bring charge – Q from A to point B is given by , W =− ( 𝑘(−𝑄)
𝑎
−
𝑘(−𝑄)
𝑎 )
15. Assertion (A) : If the amount of charge flowed in time t through a cross-section of wire isq = βt − γt2 , where β and
γ are constants.
1 2
1 3
Reason (R) : The current `i` in terms of t is given by𝑖 = 2
β𝑡 − 3 γ𝑡 .
16. Assertion (A) : Electric field is a characteristic of the system of charges and is independent of the test charge that
you place at a point to determine the field.
Reason (R) :The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge
at its centre; in other words, it has a spherical symmetry.
17. Refer to the arrangement of charges in Fig – 6 . and a Gaussian surface of radius R with Q at the centre. Then
Select the correct entity
Fig – 6
−𝑄 −𝑄
(I)total flux through the surface of the sphere is (II)field on thesurface of the sphere is 2
ε0 4π
ε0𝑅
(III)flux through the surface of sphere due to 5Q is zero. (IV)field on thesurface of sphere due to –2Q is same
Everywhere.
(A) II & IV Only (B) I & IV Only (C) I & III Only (D) I & II Only
18. A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre
is directed
(A) perpendicular to the diameter (B) parallel to the diameter
(C) at an angle tilted towards the diameter (D) at an angle tilted away from the diameter.
19. According to this diagram, the potential difference across the terminals is (internal resistance of cell = r)
(A) V = E – i r (B) V = E + i r (C) V = E (D) Zero
1
20. A metal rod of length 10 cm and a rectangular cross-section of 1cm × 2 cm is connected to a battery across
pposite faces. The resistance will be
o
1
(A) maximum when the battery is connected across 1 cm × 2 cm faces.
( B) maximum when the battery is connected across 10 cm × 1 cm faces.
1
(C) maximum when the battery is connected across 10 cm × 2 cm faces.
(D) same irrespective of the three faces.
21. Two batteries of emf ε1 and ε2 (ε2 > ε1) and internal resistances r1 and r2 respectively are connected in parallel
as shown in Fig 7
Fig 7
( A) The equivalent emf εeq of the two cells is betweenε1 and ε2, i.e. ε1< εeq < ε2.
(B) The equivalent emf εeq is smaller than ε1 .
(C) The εeq is always given by εeq = ε1 + ε2 always.
(D) εeq is independent of internal resistances r1 and r2.
22. A charge q is to be distributed on two conducting spheres. What should be the value of the charges on the
spheres so that the repulsive force between them is maximum when they are placed at a fixed distance from
each other in air?
𝑞 𝑞 𝑞 3𝑞
𝑞 2𝑞
𝑞 4𝑞
(A) and (B) and (C) and (D) and
2 2 4 4 3 3 5 5
23. Fig – 8 shows the variation of electric field intensity E versus distance x. What is the potential difference
between the points at x = 2 m and at x = 6 m from O?
Fig – 8
(A) 30 V (B) 60 V (C) 40 V (D) 80 V
24. The effective capacitance of combination of combination of equal capacitors between points A and B shown in
Fig – 9 is
Fig – 9
𝐶
𝐶
(A) (B) (C) 2𝐶 (D) 4𝐶
2 4
