CBSE Class 12 Physics Electric Charges and Fields Worksheet Set B

CBSE Class 12 Physics Electric Charges and Fields Worksheet Set B

Question. A cylinder of radius R and length l is placed in a uniform electric field E parallel to the axis of the cylinder. The total flux over the curved surface of the cylinder is
(a) zero
(b) πR²E
(c) 2πR²E
(d) E / πR²

Answer: A

Question. Two particle of equal mass m and charge q are placed at a distance of 16 cm. They do not experience any force. The value of q/m is
(a) l
(b) √πε₀/G
(c) √G/4πε₀
(d) √4πε₀G

Answer: D

Question. The spatial distribution of electric field due to charges (A, B) is shown in figure. Which one of the following statements is correct ?
(a) A is +ve and B –ve, |A| > |B|
(b) A is –ve and B +ve, |A| = |B|
(c) Both are +ve but A > B
(d) Both are –ve but A > B

Answer: A

Question. If a dipole of dipole moment P̅ is placed in a uniform electric field E̅ , then torque acting on it is given by 

Answer: B

Question. A simple pendulum has a length l , mass of bob m. The bob is given a charge q. The pendulum is suspended between the vertical plates of the charged parallel plate capacitor. If E is the field strength between the plates, then time period T equal to 

Answer: D

Question. Two identical thin rings, each of radius a meter, are coaxially placed at a distance R meter apart. If Q₁ coulomb and Q₂ coulomb are respectively the charges uniformly spread on the two rings, the work done in moving a charge q coulomb from the centre of one ring to that of the other is
(a) Zero
(b) q(Q₁-Q₂)(√2 - 1)/4√πε₀a
(c) q√2(Q₁ + Q₂)/4πε₀a
(d) q(Q₁ + Q₂)(√2+1)/4√2πε₀a

Answer: B

Question. A metallic sphere is placed in a uniform electric field. The line of force follow the path (s) shown in the figure as (21 EX 2)
(a) 1
(b) 2
(c) 3
(d) 4

Answer: D

Question. A soap bubble is given negative charge, its radius will
(a) increase
(b) decrease
(c) remain unchanged
(d) fluctuate

Answer: A

Question. A and B are two identically spherical charged bodies which repel each other with force F, kept at a finite distance. A third uncharged sphere of the same size is brought in contact with sphere B and removed. It is then kept at mid point of A and B. Find the magnitude of force on C.
(a) F/2
(b) F/8
(c) F
(d) Zero

Answer: C

Question. An electric dipole of moment P̅ is placed in a uniform electric field E̅ such that P̅ points along E̅ . If the dipole is slightly rotated about an axis perpendicular to the plane containing E̅ and P̅ and passing through the centre of the dipole, the dipole executes simple harmonic motion. Consider I to be the moment of inertia of the dipole about the axis of rotation. What is the time period of such oscillation?
(a) √(πE/ I)
(b) 2π √(I / πE)
(c) 2π √(I / 2πE)
(d) None of these

Answer: B

Question. The electric field in a certain region is acting radially outward and is given by E = Aa. A charge contained in a sphere of radius 'a' centred at the origin of the field, will be given by
(a) A ε₀ a²
(b) 4 pε₀ Aa³ 
(c) ε₀ Aa³
(d) 4 πε₀ Aa²

Answer: B

Question. There exists a non-uniform electric field along x-axis as shown in the figure below. The field increases at a uniform rate along +ve x-axis. A dipole is placed inside the field as shown. Which one of the following is correct for the dipole?
(a) Dipole moves along positive x-axis and undergoes a clockwise rotation
(b) Dipole moves along negative x-axis and undergoes a clockwise rotation
(c) Dipole moves along positive x-axis and undergoes a anticlockwise rotation
(d) Dipole moves along negative x-axis and undergoes a anticlockwise rotation

Answer: D

Question. The electric field strength at a distance r from a charge q is E. What will be electric field strength if the distance of the observation point is increased to 2 r?
(a) E/2
(b) E/4
(c) E/6
(d) None of these

Answer: B

Question. A drop of oil of density ρ and radius r carries a charge q when placed in an electric field E, it moves upwards with a velocity v. If ρ₀ is the density of air, η be the viscosity of the air, then which of the following force is directed upwards?
(a) q E
(b) 6π ηr v
(c) 4/3 πr³(ρ - ρ₀)g
(d) None of these

Answer: A

Question. ABC is an equilateral triangle. Charges +q are placed at each corner as shown as fig. The electric intensity at centre O will be

Answer: D

Question. An electric dipole is placed along the x-axis at the origin O. A point P is at a distance of 20 cm from this origin such that OP makes an angle π/3 with the x-axis. If the electric field at P makes an angle θ with the x-axis, the value of θ would be
(a) π/3
(b) π/3 + tan^-1(√3/2)
(c) 2π/3
(d) tan^-1(√3/2)

Answer: B

Question. A short electric dipole of dipole moment P̅ is placed at a distance r from the centre of a solid metallic sphere of radius a (<< r) as shown in the figure. The electric field intensity at the centre of sphere C due to induced charge on the sphere is 

Answer: B

Question. The electrostatic potential (Φ_r) of a spherical symmetric system kept at origin, is shown in the figure, and given as 

Which of the following option(s) is/are incorrect
(a) For spherical region r ≤ R₀ total electrostatic energy stored is zero
(b) Within r = 2R₀ total charge is q.
(c) There will be no charge anywhere except at r = R₀
(d) All of these 

Answer: D

Question. A solid sphereical conductor of radius R has a spherical cavity of radius a (a < R) at its centre. A charge + Q is kept at the centre. The cahrge at the inner surface, outer and at a position r (a < r < R) are respectively
(a) + Q, – Q, 0
(b) – Q, + Q, 0
(c) 0, – Q, 0
(d) + Q , 0, 0

Answer: B

Question. A charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled, then the outward electric flux will
(a) increase four times
(b) be reduced to half
(c) remain the same
(d) be doubled

Answer: C

Question. Suppose the charge of a proton and an electron differ slightly. One of them is – e, the other is (e + Δe). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then Δe is of the order of [Given mass of hydrogen mh = 1.67 × 10^–27 kg] 
(a) 10^–23C
(b) 10^–37 C
(c) 10^–47 C
(d) 10^–20 C

Answer: B

Question. A glass rod rubbed with silk is used to charge a gold leaf electroscope and the leaves are observed to diverge. The electroscope thus charged is exposed to X-rays for a short period. Then
(a) the divergence of leaves will not be affected
(b) the leaves will diverge further
(c) the leaves will collapse
(d) the leaves will melt

Answer: B

Question. The surface density on the copper sphere is s. The electric field strength on the surface of the sphere is
(a) σ
(b) σ/2
(c) Q / 2ε_o
(d) Q / ε_o

Answer: D

Question. When air is replaced by a dielectric medium of force constant K, the maximum force of attraction between two charges, separated by a distance
(a) decreases K-times
(b) increases K-times
(c) remains unchanged
(d) becomes 1/K²

Answer: A

Question. Two point charges q₁ = 4μC and q₂ = 9 μC are placed 20 cm apart. The electric field due to them will be zero on the line joining them at a distance of
(a) 8 cm from q₁
(b) 8 cm form q₂
(c) 80/13 cm from q₁
(d) 80/13 cm from q₂

Answer: A

Question. An uncharged sphere of metal is placed in between charged plates as shown. The lines of force look like 

(a) A
(b) B
(c) C
(d) D

Answer: C

Question. Force between two identical charges placed at a distance of r in vacuum is F. Now a slab of dielectric of dielectric contrant 4 is inserted between these two charges. If the thickness of the slab is r/2, then the force between the charges will become
(a) F
(b) 3/5 F
(c) 4/9 F
(d) F/2

Answer: C

              Very Short Answer

Q1)       Who found the inverse square law of force between unlike and like magnetic fields?

Q2)       What is additive property?

Q3)       What is torsion balance?

Q4)       What is charging by contact?

Q5)       What is line of force?

              Short Answer

Q6)       What is the physical significance of the electric dipole?

Q7)       What do you mean by the force between the multiple charges?

Q8)       What do you mean by the superposition principle?

Q9)       What is the physical significance of the electric field?

Q10)     What are the general important properties of the electric field lines?

              Long Answer

Q11)     What do you mean by Gauss’s Law and what are its applications?

Q12)     Write short note on electric dipole?

Q13)     State the difference between electric field and magnetic field?

Q14)     Explain electric field and electric field lines?

Q15)     What are the important points to remember Gauss’s Law?