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Electrostatic Potential and Capacitance MCQs

Class 12 Physics — questions with answers and worked explanations.

20 free questions Class 12 Physics Answers + explanations No sign-up

These questions are drawn from the Pariksha Sutra question bank for Electrostatic Potential and Capacitance, part of the Class 12 Physics syllabus. Each one shows the correct answer and, where a method helps, the working behind it.

Read the question, decide your answer before looking, then check the explanation — that is what turns practice into marks. If a question catches you out, the explanation is the part worth re-reading.

Questions

Question 1
The electric potential at a distance of 0.3 m from a point charge of 2x10^-9 C is (take k = 9x10^9 N m^2/C^2):
  1. 120 V
  2. 90 V
  3. 60 V
  4. 30 V
Answer: 60 V
Question 2
When a dielectric of constant K is fully inserted between the plates of a capacitor, its capacitance:
  1. becomes zero
  2. decreases K times
  3. increases K times
  4. remains unchanged
Answer: increases K times
Question 3
A charged capacitor is disconnected from the battery and a dielectric slab (K > 1) is inserted. The potential difference across the plates:
  1. remains the same
  2. becomes infinite
  3. decreases
  4. increases
Answer: decreases
Question 4
A dipole in a uniform electric field has minimum potential energy when it is:
  1. perpendicular to the field
  2. aligned parallel to the field
  3. anti-parallel to the field
  4. at 45 degrees to the field
Answer: aligned parallel to the field
Question 5
The capacitance of a parallel plate capacitor of plate area A and separation d in vacuum is given by:
  1. epsilon_0 A / d
  2. epsilon_0 A d
  3. A d / epsilon_0
  4. epsilon_0 d / A
Answer: epsilon_0 A / d
Question 6
A parallel plate capacitor is charged and then disconnected from the battery. If a dielectric slab is now inserted, the charge on the plates:
  1. increases
  2. remains the same
  3. decreases
  4. becomes zero
Answer: remains the same
Question 7
The potential energy of a dipole of moment p placed at angle theta in a uniform field E is:
  1. -pE sin(theta)
  2. pE sin(theta)
  3. pE cos(theta)
  4. -pE cos(theta)
Answer: -pE cos(theta)
Question 8
The electric field of 200 V/m is equivalent to a potential gradient of:
  1. 2 V/m
  2. 200 V/m
  3. 200 V
  4. 0.005 V/m
Answer: 200 V/m
Question 9
Electric potential at a point is defined as the work done per unit charge in bringing a test charge from infinity to that point. Its SI unit is:
  1. coulomb per volt
  2. volt
  3. newton per coulomb
  4. joule
Answer: volt
Question 10
Two capacitors of 3 mu-F and 6 mu-F are connected in series. The equivalent capacitance is:
  1. 18 mu-F
  2. 4.5 mu-F
  3. 2 mu-F
  4. 9 mu-F
Answer: 2 mu-F
Question 11
A capacitor stays connected to a battery of EMF V. When a dielectric slab is inserted, the charge stored:
  1. increases
  2. becomes zero
  3. remains the same
  4. decreases
Answer: increases
Question 12
Electric field lines and equipotential surfaces always intersect each other at an angle of:
  1. 45 degrees
  2. 0 degrees
  3. 90 degrees
  4. 180 degrees
Answer: 90 degrees
Question 13
The potential energy of a system of two point charges 4x10^-6 C and 2x10^-6 C separated by 0.6 m is (k = 9x10^9 N m^2/C^2):
  1. 0.24 J
  2. 0.06 J
  3. 0.18 J
  4. 0.12 J
Answer: 0.12 J
Question 14
Three capacitors of 2 mu-F, 3 mu-F and 5 mu-F are connected in parallel. The equivalent capacitance is:
  1. 10 mu-F
  2. 1.03 mu-F
  3. 0.97 mu-F
  4. 30 mu-F
Answer: 10 mu-F
Question 15
The capacitance of an isolated conducting sphere of radius R is:
  1. epsilon_0 R
  2. R / (4 pi epsilon_0)
  3. 4 pi epsilon_0 R
  4. 4 pi epsilon_0 R^2
Answer: 4 pi epsilon_0 R
Question 16
Two capacitors 2 mu-F and 4 mu-F are connected in series across 60 V. The voltage across the 2 mu-F capacitor is:
  1. 40 V
  2. 20 V
  3. 60 V
  4. 30 V
Answer: 40 V
Question 17
The work done in moving a charge along an equipotential surface is:
  1. equal to qV
  2. zero
  3. infinite
  4. maximum
Answer: zero
Question 18
The energy stored in a 4 mu-F capacitor charged to 200 V is:
  1. 0.16 J
  2. 0.8 J
  3. 0.08 J
  4. 0.04 J
Answer: 0.08 J
Question 19
A charge of 3 C is moved through a potential difference of 12 V. The work done is:
  1. 36 J
  2. 0.25 J
  3. 4 J
  4. 15 J
Answer: 36 J
Question 20
In a uniform electric field directed along the x-axis, the equipotential surfaces are planes:
  1. spherical
  2. parallel to the x-axis
  3. inclined at 45 degrees
  4. perpendicular to the x-axis
Answer: perpendicular to the x-axis

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