Electrostatics

36 free MDCAT Physics MCQs on Electrostatics (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 36 questions

1. Question 1

   The study of electric charges at rest and the forces between them is called:
   • AElectrostatics
   • BElectrodynamics
   • CElectromagnetism
   • DElectronics
   Show answer and explanation

   Answer: A) Electrostatics

   Charges in motion are studied in current electricity. Source: 11 Physics Book FBISE, p. 185.

2. Question 2

   The rate of change of electric potential with respect to displacement is called the:
   • APotential gradient
   • BPotential energy
   • CField flux
   • DCapacitance
   Show answer and explanation

   Answer: A) Potential gradient

   E = -Delta V / Delta r. Source: 11 Physics Book FBISE, p. 194.

3. Question 3

   The work done in bringing a unit positive charge from infinity to a point, keeping it in equilibrium, is the:
   • AElectric flux at that point
   • BElectric field at that point
   • CCapacitance of that point
   • DElectric potential at that point
   Show answer and explanation

   Answer: D) Electric potential at that point

   For a point charge, V = kQ/r. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 91.

4. Question 4

   In an RC circuit, the time during which 63.2% of the maximum charge is deposited on the capacitor plates is the:
   • ATime constant
   • BHalf-life
   • CTime period
   • DRelaxation time
   Show answer and explanation

   Answer: A) Time constant

   Time constant = RC. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 98.

5. Question 5

   The permittivity of free space has the value:
   • A6.67 x 10^-11 C2 N-1 m-2
   • B9.00 x 10^9 C2 N-1 m-2
   • C1.60 x 10^-19 C2 N-1 m-2
   • D8.85 x 10^-12 C2 N-1 m-2
   Show answer and explanation

   Answer: D) 8.85 x 10^-12 C2 N-1 m-2

   k = 1/(4 pi epsilon0) = 9 x 10^9 N m2 C-2. Source: 11 Physics Book FBISE, p. 185.

6. Question 6

   In SI units, with vacuum between the charges, Coulomb's constant k is:
   • A9 x 10^9 N m2 C-2
   • B8.85 x 10^-12 N m2 C-2
   • C6.67 x 10^-11 N m2 C-2
   • D1.6 x 10^-19 N m2 C-2
   Show answer and explanation

   Answer: A) 9 x 10^9 N m2 C-2

   Its value depends on the medium and the system of units. Source: 11 Physics Book FBISE, p. 186.

7. Question 7

   The formula for the electrostatic force between charges was proposed by the French physicist:
   • AMichael Faraday
   • BCharles Coulomb
   • CIsaac Newton
   • DAlessandro Volta
   Show answer and explanation

   Answer: B) Charles Coulomb

   Coulomb lived 1736-1806. Source: 11 Physics Book FBISE, p. 185.

8. Question 8

   The concept of a field, in the context of electric forces, was developed by:
   • AJames Maxwell
   • BCharles Coulomb
   • CMichael Faraday
   • DIsaac Newton
   Show answer and explanation

   Answer: C) Michael Faraday

   Faraday also introduced electric field lines. Source: 11 Physics Book FBISE, p. 188.

9. Question 9

   The SI unit of electric field intensity is newton per coulomb or:
   • ANewton per metre
   • BJoule per coulomb
   • CCoulomb per volt
   • DVolt per metre
   Show answer and explanation

   Answer: D) Volt per metre

   Both units are equivalent. Source: 11 Physics Book FBISE, p. 189.

10. Question 10

    A capacitor stores energy in the form of:
    • AElectric field
    • BMagnetic field
    • CChemical energy
    • DKinetic energy
    Show answer and explanation

    Answer: A) Electric field

    E = 1/2 QV. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 96.

11. Question 11

    The resting bioelectric potential across a cell membrane is typically about:
    • A5 millivolts
    • B50 millivolts
    • C500 millivolts
    • D220 millivolts
    Show answer and explanation

    Answer: B) 50 millivolts

    Nerve and muscle membranes are slightly permeable to K+ ions. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 100.

12. Question 12

    Electric eels stun their prey by delivering shocks of up to:
    • A220 volts
    • B50 volts
    • C860 volts
    • D8600 volts
    Show answer and explanation

    Answer: C) 860 volts

    They are electrogenic animals. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 101.

13. Question 13

    When a fully charged capacitor discharges through a resistor, the charge left on its plates after one time constant is about:
    • A0%
    • B63.2%
    • C50.0%
    • D36.7%
    Show answer and explanation

    Answer: D) 36.7%

    Q = Q0 e^-1 = 0.367 Q0. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 99.

14. Question 14

    While charging through a resistor, the charge on a capacitor after one time constant RC is about what percentage of its maximum?
    • A63.2%
    • B36.7%
    • C100%
    • D50.0%
    Show answer and explanation

    Answer: A) 63.2%

    Q = Q0 (1 - e^-1) = 0.632 Q0. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 98.

15. Question 15

    At a point near a point charge, the electric field is 24 N/C and the electric potential is 6 J/C. The distance of the point from the charge is:
    • A144 m
    • B4.0 m
    • C0.25 m
    • D0.5 m
    Show answer and explanation

    Answer: C) 0.25 m

    r = V/E = 6/24 = 0.25 m. Source: 11 Physics Book FBISE, p. 192.

16. Question 16

    A point charge produces an electric field of 2.5 N/C at 0.5 m from it. The potential at that point is:
    • A2.5 V
    • B5.0 V
    • C0.2 V
    • D1.25 V
    Show answer and explanation

    Answer: D) 1.25 V

    V = E r = 2.5 x 0.5 = 1.25 V. Source: 11 Physics Book FBISE, p. 196.

17. Question 17

    An object carrying 24 uC floats in a uniform vertical electric field of 610 N/C. Its mass is about:
    • A1.5 g
    • B15 g
    • C0.15 g
    • D3.0 g
    Show answer and explanation

    Answer: A) 1.5 g

    mg = qE, so m = (24e-6 x 610)/9.8 = 1.5 x 10^-3 kg. Source: 11 Physics Book FBISE, p. 196.

18. Question 18

    The magnitude of a point charge that would create an electric field of 1.00 N/C at a point 1.00 m away is about:
    • A9.00 x 10^9 C
    • B1.11 x 10^-10 C
    • C1.00 C
    • D8.85 x 10^-12 C
    Show answer and explanation

    Answer: B) 1.11 x 10^-10 C

    q = E r^2 / k = 1/(9 x 10^9) = 1.11 x 10^-10 C. Source: 11 Physics Book FBISE, p. 196.

19. Question 19

    A parallel plate capacitor has plates of area 1.00 m2 separated by 1.00 mm of air. Its capacitance is:
    • A885 nF
    • B88.5 nF
    • C0.885 nF
    • D8.85 nF
    Show answer and explanation

    Answer: D) 8.85 nF

    C = A epsilon0 / d = 8.85 x 10^-12 / 10^-3 = 8.85 x 10^-9 F. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 94.

20. Question 20

    An 8.85 nF capacitor is connected to 3.00 x 10^3 V. The charge stored on it is:
    • A26.6 uC
    • B2.66 uC
    • C8.85 uC
    • D339 uC
    Show answer and explanation

    Answer: A) 26.6 uC

    Q = CV = 8.85 x 10^-9 x 3000 = 26.6 x 10^-6 C. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 94.

21. Question 21

    Capacitors of 4 uF and 8 uF are connected in series. Their equivalent capacitance is about:
    • A12 uF
    • B2.66 uF
    • C0.375 uF
    • D32 uF
    Show answer and explanation

    Answer: B) 2.66 uF

    1/C = 1/4 + 1/8 = 3/8, so C = 2.66 uF (book value). Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 96.

22. Question 22

    A 50 F capacitor is charged to a potential of 100 V. The energy stored in it is:
    • A5 kJ
    • B500 kJ
    • C250 kJ
    • D2.5 kJ
    Show answer and explanation

    Answer: C) 250 kJ

    E = 1/2 C V^2 = 0.5 x 50 x 10^4 = 2.5 x 10^5 J. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 98.

23. Question 23

    A heart defibrillator delivers 4 x 10^2 J by discharging a capacitor initially at 1 x 10^4 V. Its capacitance is:
    • A0.8 uF
    • B4 uF
    • C80 uF
    • D8 uF
    Show answer and explanation

    Answer: D) 8 uF

    C = 2E/V^2 = 800/10^8 = 8 x 10^-6 F. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 104.

24. Question 24

    Two charges of the same sign:
    • ARepel each other
    • BAttract each other
    • CExert no force
    • DNeutralize each other
    Show answer and explanation

    Answer: A) Repel each other

    Unlike charges attract. Source: 11 Physics Book FBISE, p. 186.

25. Question 25

    Unlike gravitational forces, which are always attractive, electric forces can be:
    • AOnly attractive
    • BAttractive or repulsive
    • CIndependent of distance
    • DOnly contact forces
    Show answer and explanation

    Answer: B) Attractive or repulsive

    Both are inverse-square field forces. Source: 11 Physics Book FBISE, p. 187.

26. Question 26

    For a point outside an isolated charged sphere, the sphere behaves as if its charge were:
    • ASpread evenly over its outer surface
    • BSpread over a flat charged sheet
    • CZero at every point outside it
    • DA point charge at its center
    Show answer and explanation

    Answer: D) A point charge at its center

    This holds only if no other charged object is nearby. Source: 11 Physics Book FBISE, p. 186.

27. Question 27

    The direction of the electric field at a point is the direction in which a:
    • APositive test charge tends to move
    • BNegative test charge tends to move
    • CNeutral particle tends to move
    • DElectron stays at rest
    Show answer and explanation

    Answer: A) Positive test charge tends to move

    E is directed from positive to negative charges. Source: 11 Physics Book FBISE, p. 189.

28. Question 28

    Since E = -Delta V / Delta r, the electric potential increases in the direction:
    • AAlong the electric field
    • BOpposite to the electric field
    • CPerpendicular to the field
    • DOf the field lines' ends
    Show answer and explanation

    Answer: B) Opposite to the electric field

    The negative sign shows potential falls along the field. Source: 11 Physics Book FBISE, p. 192.

29. Question 29

    For capacitors connected in series, the equivalent capacitance is:
    • ALarger than any individual one
    • BLess than any individual one
    • CEqual to their simple sum
    • DEqual to the largest one
    Show answer and explanation

    Answer: B) Less than any individual one

    1/C = 1/C1 + 1/C2 + ... Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 101.

30. Question 30

    When capacitors are joined in parallel, their combined capacitance is always:
    • AEqual to the smallest one
    • BLess than any individual one
    • CLarger than any individual one
    • DEqual to their product
    Show answer and explanation

    Answer: C) Larger than any individual one

    C = C1 + C2 + ... Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 101.

31. Question 31

    In a series combination of capacitors, every capacitor carries the same:
    • AEnergy
    • BVoltage
    • CCapacitance
    • DCharge
    Show answer and explanation

    Answer: D) Charge

    Charge is induced equally on each by electrostatic induction. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 94.

32. Question 32

    The energy stored in a capacitor equals the area under its graph of:
    • APotential difference against charge
    • BCurrent against the time
    • CCharge against the time
    • DCapacitance against voltage
    Show answer and explanation

    Answer: A) Potential difference against charge

    Area of the triangle = 1/2 QV. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 96.

33. Question 33

    Reducing the resistance in an RC circuit makes the capacitor charge and discharge:
    • ASlower
    • BFaster
    • CNot at all
    • DAt the same rate
    Show answer and explanation

    Answer: B) Faster

    A smaller time constant RC means a faster rate. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 99.

34. Question 34

    While a capacitor is charging through a resistor, the current is:
    • AConstant throughout
    • BZero at the start
    • CHighest at the start
    • DHighest at the end
    Show answer and explanation

    Answer: C) Highest at the start

    It gradually decreases to zero. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 98.

35. Question 35

    Inside a hollow conductor such as a Faraday cage, the electric field is:
    • AUniform
    • BMaximum
    • CDoubled
    • DZero
    Show answer and explanation

    Answer: D) Zero

    Charge stays on the outer surface, shielding the inside. Source: 11 Physics Book FBISE, p. 194.

36. Question 36

    In bioelectricity, the cell membrane acts like a:
    • ACapacitor
    • BResistor
    • CBattery
    • DInductor
    Show answer and explanation

    Answer: A) Capacitor

    It stores energy as charged ions on opposite sides. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 100.

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