150 Important MCQs (Set-2 of Basic to Expert Level MCQs) on Electrostatics, Physics (Unit-Wise MCQs Practice):

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This post contains carefully selected Multiple-Choice Questions (MCQs) (Set-2 from Basic to Expert Level) from Electrostatics of Physics, prepared strictly according to the latest board exam syllabus. These MCQs include a balanced combination of conceptual understanding and numerical problem-solving, making them revision-friendly, exam-oriented, and high-scoring.

Whether you are preparing for annual board examinations, chapter tests, or competitive entry tests, this comprehensive MCQ collection thoroughly covers the fundamental principles of electrostatics—starting from Coulomb’s law (by Charles-Augustin de Coulomb) to Gauss’s law (by Carl Friedrich Gauss)—helping students build strong conceptual clarity and numerical confidence.

This unit-wise MCQ set includes questions from:

• Coulomb’s law and force between point charges in vacuum and media
• Electric field due to a point charge and multiple charges
• Concept of electric field and electric field strength (E = F/q)
• Numerical problems using $E = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}$
• Electric field lines and their graphical representation
• Electric dipole and basic dipole concepts
• Electric flux and flux through closed surfaces
• Statement and applications of Gauss’s law
• Electric field due to infinite charged plates and hollow spherical conductors
• Electric field between oppositely charged parallel plates (including edge effects)
• Electric potential and work done (V = W/q)
• Relationship between electric field and potential (potential gradient)

Each MCQ is provided with the correct answer and a clear, concise explanation, helping students to:

Strengthen conceptual understanding of electrostatic phenomena
Avoid common mistakes in electric field and potential numericals
Improve problem-solving skills involving Coulomb’s law, Gauss’s law, and flux
Master diagrams of field lines and charge distributions
Achieve maximum marks in the MCQ section

This all-in-one Electrostatics MCQ collection is an essential revision tool for all students aiming to excel in Physics exams and fully master the concepts of electric charges, fields, flux, Gauss’s law, and electric potential.

MCQs No. 1

Photo diode is used for detection of:

a. Heat
b. Magnet
c. Current
d. Light

Correct answer: d. Light

Explanation:
A photodiode converts light energy into electrical signals, so it is used to detect light.

MCQs No. 2

A two-input NAND gate with inputs A and B has output 0 if:

a. B is zero
b. A is zero
c. Both A and B are 1
d. Both A and B are 0

Correct answer: c. Both A and B are 1

Explanation:
From the truth table of NAND gate, output becomes 0 only when both inputs are 1.

MCQs No. 3

For normal operation of transistor, the emitter–base junction is always:

a. Forward biased
b. Reverse biased
c. Unbiased
d. Grounded

Correct answer: a. Forward biased

Explanation:
For proper transistor action, E–B junction is forward biased while C–B junction is reverse biased.

MCQs No. 4

The central region of a transistor is called:

a. Base
b. Emitter
c. Collector
d. Neutral

Correct answer: a. Base

Explanation:
Base is the thin, lightly doped central region of a transistor.

MCQs No. 5

In p-type substances, the majority charge carriers are:

a. Electrons
b. Protons
c. Holes
d. Neutrons

Correct answer: c. Holes

Explanation:
Trivalent impurities create holes, making them majority carriers.

MCQs No. 6

When A = 0 and B = 1, output of NAND gate is:

a. 0
b. 0.1
c. 1
d. 0.8

Correct answer: c. 1

Explanation:
X = (A·B)̅ = (0·1)̅ = 0̅ = 1

MCQs No. 7

At what angle between electric field and area vector is electric flux half of maximum?

a. 30°
b. 60°
c. 45°
d. 90°

Correct answer: b. 60°

Explanation:
Φ = Φmax cosθ → Φ = Φmax/2 ⇒ cosθ = 1/2 ⇒ θ = 60°

MCQs No. 8

Boolean expression of NAND gate is:

a. A − B
b. A + B
c. A · B
d. X = (A · B)̅

Correct answer: d. X = (A · B)̅

Explanation:
NAND is NOT of AND operation.

MCQs No. 9

Automatic functioning of street light can be done by:

a. Inductor
b. Capacitor
c. Transistor
d. Comparator

Correct answer: d. Comparator

Explanation:
Comparators compare light levels and control switching automatically.

MCQs No. 10

Colour of light emitted by LED depends upon:

a. Forward bias
b. Reverse bias
c. Type of material
d. Arsenic

Correct answer: c. Type of material

Explanation:
Different semiconductor materials emit different colours.

MCQs No. 11

In full-wave rectification, number of diodes required is:

a. 3
b. 5
c. 4
d. 1

Correct answer: c. 4

Explanation:
Bridge rectifier uses four diodes.

MCQs No. 12

A diode characteristic curve is plotted between:

a. Current and resistance
b. Voltage and time
c. Voltage and current
d. Current and time

Correct answer: c. Voltage and current

Explanation:
V–I graph shows diode behavior.

MCQs No. 13

SI unit of current gain β is:

a. Ampere
b. Volt
c. Coulomb
d. No unit

Correct answer: d. No unit

Explanation:
β is a ratio of currents, so it is dimensionless.

MCQs No. 14

Conversion of only one half of AC into DC is called:

a. Half wave amplification
b. Wave amplification
c. Half wave electrification
d. Half wave rectification

Correct answer: d. Half wave rectification

Explanation:
Only one half cycle is converted into DC.

MCQs No. 15

Which one is sure test for presence of charge?

a. Attraction
b. Repulsion
c. Both
d. None

Correct answer: b. Repulsion

Explanation:
Attraction may occur with neutral body, but repulsion confirms charge.

MCQs No. 16

SI unit of electric flux is:

a. N m C²
b. C² N⁻¹ m⁻¹
c. N m C⁻²
d. N m² C⁻¹

Correct answer: d. N m² C⁻¹

Explanation:
Φ = EA → units = Nm²C⁻¹

MCQs No. 17

The study of charges at rest is called:

a. Electromagnetism
b. Electric induction
c. Electricity
d. Electrostatics

Correct answer: d. Electrostatics

Explanation:
Electrostatics deals with stationary charges.

MCQs No. 18

Value of Coulomb constant K is:

a. 9 × 10⁹ Nm²C⁻²
b. 8.85 × 10⁻¹² C²N⁻¹m⁻²
c. 9 × 10⁻⁹
d. 8.85 × 10⁻¹²

Correct answer: a. 9 × 10⁹ Nm²C⁻²

Explanation:

K = 1 / (4πϵ₀) = 9 × 10⁹ Nm²C⁻²

Got it — thanks for pointing that out 👍
Here’s the regenerated part with clear explanations added everywhere (continuing from your last section, MCQs No. 19 onward):

MCQs No. 19

If magnitude of both charges is doubled and distance between them is halved, electric force becomes:

a. 4 times
b. 8 times
c. 16 times
d. 2 times

Correct answer: c. 16 times

Explanation:
Using Coulomb’s law:

F = k(q₁q₂ / r²)

After change:

F′ = k(2q₁·2q₂)/(r/2)² = 16F

So force becomes 16 times.

MCQs No. 20

Coulomb’s force:

a. Obeys inverse square law
b. Depends on magnitude of charges
c. Depends on medium
d. All of these

Correct answer: d. All of these

Explanation:
Coulomb’s force depends on charges, distance, and medium:

F = (1/4πϵ₀)(q₁q₂ / r²)

MCQs No. 21

Conventionally attractive force is taken as _____ and repulsive force as _____:

a. Positive, Positive
b. Positive, Negative
c. Negative, Positive
d. Negative, Negative

Correct answer: c. Negative, Positive

Explanation:
By sign convention, attraction is negative and repulsion is positive.

MCQs No. 22

Electric field due to a point charge depends on:

a. Magnitude of charge
b. Distance
c. Medium
d. All of these

Correct answer: d. All of these

Explanation:
E = (1/4πϵ₀)(q / r²), so it depends on q, r, and medium.

MCQs No. 23

If potential difference is doubled and distance is halved, electric field:

a. Doubled
b. Halved
c. Increased by 3 times
d. Increased by 4 times

Correct answer: d. Increased by 4 times

Explanation:
E = V/d
E′ = 2V/(d/2) = 4E

MCQs No. 24

Idea of electric field lines was proposed by:

a. Ampere
b. Faraday
c. Gauss
d. Coulomb

Correct answer: b. Faraday

Explanation:
Faraday introduced the concept of electric field lines.

MCQs No. 25

Tangent to electric field line gives direction of:

a. Force
b. Intensity
c. Both A and B
d. Charge

Correct answer: c. Both A and B

Explanation:
Electric force and electric field intensity act along tangent.

MCQs No. 26

Number of field lines per unit perpendicular area is electric:

a. Force
b. Intensity
c. Flux
d. Charge

Correct answer: b. Intensity

Explanation:
Electric intensity E = N/A⊥.

MCQs No. 27

In photocopier, drum is given _____ charge and toner _____ charge:

a. Positive, Negative
b. Positive, Positive
c. Negative, Positive
d. Negative, Negative

Correct answer: a. Positive, Negative

Explanation:
Opposite charges attract toner toward drum image.

MCQs No. 28

Heart of photocopier is:

a. Drum
b. Toner
c. Rollers
d. Cartridge

Correct answer: a. Drum

Explanation:
Drum forms electrostatic image.

MCQs No. 29

Electric flux is maximum when θ equals:

a. 0°
b. 90°
c. 180°
d. 270°

Correct answer: a. 0°

Explanation:
Φ = EA cosθ → maximum when cosθ = 1.

MCQs No. 30

Electric flux through closed surface does NOT depend on:

a. Charge enclosed
b. Medium
c. Shape of surface
d. Both A and B

Correct answer: c. Shape of surface

Explanation:
By Gauss’s law, flux depends only on enclosed charge.

MCQs No. 31

Which is true for oppositely charged plates?

a. Electric field constant
b. Potential difference constant
c. Potential zero at midpoint
d. All of these

Correct answer: d. All of these

Explanation:
Parallel plates produce uniform field; midpoint potential is zero.

MCQs No. 32

Potential energy gained by 5 C charge moved 5 m in 10 N/C field:

a. 25 J
b. 200 J
c. 2 J
d. 250 J

Correct answer: d. 250 J

Explanation:
ΔU = qEd = 5×10×5 = 250 J.

MCQs No. 33

An ECG records:

a. Current
b. Charge
c. Voltage
d. Field

Correct answer: c. Voltage

Explanation:
ECG measures potential difference on skin.

MCQs No. 34

For equal opposite charges at midpoint:

a. V = 0
b. E ≠ 0
c. ΔV ≠ 0
d. All of these

Correct answer: d. All of these

Explanation:
Potentials cancel but fields add.

MCQs No. 35

Potential gradient for E = 10 N/C is:

a. −1 Vm⁻¹
b. +10 Vm⁻¹
c. −10 Vm⁻¹
d. +1 Vm⁻¹

Correct answer: c. −10 Vm⁻¹

Explanation:
E = −dV/dr.

MCQs No. 36

One joule equals:

a. 1 W s
b. 6.25×10¹⁸ eV
c. 10⁷ erg
d. All of these

Correct answer: d. All of these

Explanation:
All are equivalent energy units.

Great — here’s the remaining Capacitor + Dielectric MCQs (with complete explanations) in the same pattern:

MCQs No. 37

A capacitor has capacitance 10 μF with dielectric constant 2. If dielectric is removed, capacitance becomes:

a. 20 μF
b. 5 μF
c. 10 μF
d. 40 μF

Correct answer: b. 5 μF

Explanation:
Cvac = Cmed / εr = 10 / 2 = 5 μF

MCQs No. 38

Due to polarization of dielectric in capacitor:

a. Surface charge density decreases
b. Electric intensity decreases
c. Potential difference decreases
d. All of these

Correct answer: d. All of these

Explanation:
Insertion of dielectric reduces σ, E, and V by factor εr.

MCQs No. 39

Energy stored in isolated charged capacitor after inserting dielectric:

a. Increases
b. Decreases
c. Remains same
d. Becomes zero

Correct answer: b. Decreases

Explanation:
Umed = Uvac / εr
So stored energy decreases.

MCQs No. 40

Two capacitors 5 μF and 10 μF are in series across 15 V. Voltage across 5 μF is:

a. 5 V
b. 10 V
c. 15 V
d. 20 V

Correct answer: b. 10 V

Explanation:
V₁ = (C₂/(C₁ + C₂))V
= (10/(5+10))×15 = 10 V

MCQs No. 41

A 10 μF capacitor at 50 V is connected to uncharged capacitor. Final voltage is 20 V. Second capacitor is:

a. 20 μF
b. 10 μF
c. 30 μF
d. 15 μF

Correct answer: d. 15 μF

Explanation:
Initial charge Q = CV = 10×50 = 500 μC
Ctotal = Q/V = 500/20 = 25 μF
C₂ = 25 − 10 = 15 μF

MCQs No. 42

Electric potential energy per unit charge is:

a. Electric flux
b. Electric potential
c. Electric field
d. Electric intensity

Correct answer: b. Electric potential

Explanation:
V = U/q

MCQs No. 43

Force on 4 C charge in field of 4 N/C:

a. 8 N
b. 16 N
c. 4 N
d. 1 N

Correct answer: b. 16 N

Explanation:
F = qE = 4×4 = 16 N

MCQs No. 44

Equation Φ = E·A applies to:

a. Cylindrical surface
b. Conical surface
c. Flat surface
d. Spherical surface

Correct answer: c. Flat surface

Explanation:
Formula is valid only for plane surfaces.

MCQs No. 45

Photocopier and inkjet printer are applications of:

a. Electricity
b. Electrostatics
c. Magnetism
d. Electromagnetism

Correct answer: b. Electrostatics

Explanation:
They use electrostatic attraction of toner.

MCQs No. 46

Force on electron in field 10⁸ N/C:

a. 1.6×10⁻⁸ N
b. 1.6×10⁻¹¹ N
c. 1.6×10⁻¹⁹ N
d. 1.6×10⁻²⁷ N

Correct answer: b. 1.6×10⁻¹¹ N

Explanation:
F = qE = 1.6×10⁻¹⁹ × 10⁸

MCQs No. 47

Photoconductor is:

a. Mercury
b. Aluminum
c. Copper
d. Selenium

Correct answer: d. Selenium

Explanation:
Selenium conducts when light falls on it.

MCQs No. 48

Due to polarization, electric field inside capacitor:

a. Increases
b. Decreases
c. Same
d. First increases

Correct answer: b. Decreases

Explanation:
Dielectric reduces effective field.

MCQs No. 49

Energy gained by charge 2e across 3 V:

a. 9.6×10⁻¹⁸ J
b. 9.6×10⁻¹⁹ J
c. 1.6×10⁻¹⁹ J
d. 9.6×10⁻¹⁷ J

Correct answer: b. 9.6×10⁻¹⁹ J

Explanation:
U = qV = 2e×3 = 6eV = 9.6×10⁻¹⁹ J

MCQs No. 50

Electric eel can generate potential up to:

a. 160 V
b. 220 V
c. 440 V
d. 600 V

Correct answer: d. 600 V

Explanation:
Electric eel can produce very high voltage for defence.

MCQs No. 51

If time constant in RC circuit is small, then capacitor is charged or discharged:

a. Slowly
b. Rapidly
c. At constant rate
d. Intermittently

Correct answer: b. Rapidly

Explanation:
Time constant RC represents charging time. Smaller RC means less time, so charging and discharging occur rapidly.

MCQs No. 52

Unit of RC is:

a. Farad
b. Coulomb
c. Joule
d. Ampere

Correct answer: a. Farad

Explanation:
RC is called time constant. Since R is in ohm and C in farad, RC has unit of second.

MCQs No. 53

To suspend a proton of charge q and mass m in an electric field, required field is:

a. E = mg/q
b. E = q/mg
c. E = mgq
d. E = qv/b

Correct answer: a. E = mg/q

Explanation:
For equilibrium: electric force = weight
qE = mg ⇒ E = mg/q

MCQs No. 54

If electrostatic force in vacuum is 42 N and εᵣ = 2.1, force in medium is:

a. 42 N
b. 84 N
c. 20 N
d. 2 N

Correct answer: c. 20 N

Explanation:
Force in medium is reduced by dielectric:
F = F₀ / εᵣ = 42 / 2.1 = 20 N

MCQs No. 55

Electric field inside a hollow charged sphere is:

a. 10 N C⁻¹
b. Zero
c. 2.5 N C⁻¹
d. 5×10⁻⁶ N C⁻¹

Correct answer: b. Zero

Explanation:
According to Gauss’s law, electric field inside a hollow conducting sphere is zero.

MCQs No. 56

Which relation is correct?

a. Joule = volt × ampere
b. Joule = coulomb/volt
c. Joule = volt
d. Joule = coulomb × volt

Correct answer: d. Joule = coulomb × volt

Explanation:
Work done W = qV, so joule = coulomb × volt.

MCQs No. 57

Coulomb per volt is called:

a. Farad
b. Ampere
c. Joule
d. Henry

Correct answer: a. Farad

Explanation:
C = q/V, unit of capacitance is farad.

MCQs No. 58

Capacitance of capacitor depends on:

a. Thickness of plates
b. Charge
c. Voltage
d. Geometry

Correct answer: d. Geometry

Explanation:
Capacitance depends on plate area and separation: C = ε₀A/d.

MCQs No. 59

Electrostatics is study of:

a. Electric current
b. Stationary charges
c. Moving charges
d. Magnetism

Correct answer: b. Stationary charges

Explanation:
Electrostatics deals with charges at rest.

MCQs No. 60

When dielectric inserted between capacitor plates, capacitance:

a. Decreases
b. Increases
c. Zero
d. Infinite

Correct answer: b. Increases

Explanation:
Dielectric increases capacitance by factor εᵣ.

MCQs No. 61

Electric potential at midpoint of electric dipole is:

a. 0 V
b. 0.5 V
c. 1 V
d. 1.5 V

Correct answer: a. 0 V

Explanation:
Potential due to +q and −q cancel each other.

MCQs No. 62

Relative permittivity of air is approximately:

a. 1.6
b. 1.06
c. 1.006
d. 1.0006

Correct answer: d. 1.0006

Explanation:
Air behaves almost like vacuum.

MCQs No. 63

In photocopier, toner carries:

a. Positive charge
b. Negative charge
c. Neutral
d. Alternating charge

Correct answer: b. Negative charge

Explanation:
Negatively charged toner sticks to positively charged image areas.

MCQs No. 64

Drum of photocopier is made of:

a. Copper
b. Toner
c. Selenium
d. Aluminium

Correct answer: d. Aluminium

Explanation:
Photocopier drum is made of aluminium coated with photoconductive material.

MCQs No. 65

Material used to increase capacitance:

a. Copper
b. Mica
c. Iron
d. Tin

Correct answer: b. Mica

Explanation:
Mica is a dielectric; inserting it increases capacitance.

MCQs No. 66

NC⁻¹ is unit of:

a. Force
b. Charge
c. Current
d. Electric intensity

Correct answer: d. Electric intensity

Explanation:
Electric field E = F/q, unit N/C.

MCQs No. 67

Energy gained by two electrons across 3 V is:

a. 1.6×10⁻¹⁹ J
b. 6.6×10⁻¹⁹ J
c. 3 eV
d. 6 eV

Correct answer: d. 6 eV

Explanation:
Energy = qV = 2e × 3 = 6 eV.

MCQs No. 68

RC factor has dimension of:

a. Voltage
b. Resistance
c. Time
d. Capacitance

Correct answer: c. Time

Explanation:
RC is called time constant.

MCQs No. 69

Unit of electric field other than N/C is:

a. VA
b. Vm⁻¹
c. VC
d. NC

Correct answer: b. Vm⁻¹

Explanation:
E = V/m.

MCQs No. 70

Force between two unit charges 1 m apart in air is:

a. 1 N
b. 9×10⁹ N
c. 9×10⁻⁹ N
d. Zero

Correct answer: b. 9×10⁹ N

Explanation:
From Coulomb’s law: F = k = 9×10⁹ N.

MCQs No. 71

Presence of dielectric always:

a. Reduces force
b. Increases force
c. No effect
d. Doubles force

Correct answer: a. Reduces force

Explanation:
Dielectric reduces force by factor εᵣ.

MCQs No. 72

Direction of field lines from +q is:

a. Circular
b. Curved
c. Radially outward
d. Radially inward

Correct answer: c. Radially outward

Explanation:
Electric field lines originate from positive charges.

MCQs No. 73

If charge becomes 2Q, stored energy becomes:

a. 2w
b. 4w
c. w/2
d. w/4

Correct answer: b. 4w

Explanation:
Energy ∝ Q², so doubling Q makes energy four times.

MCQs No. 74

Closeness of field lines indicates:

a. Direction
b. Strength
c. Potential
d. Uniformity

Correct answer: b. Strength

Explanation:
Closer lines mean stronger electric field.

MCQs No. 75

Minimum indivisible charge is:

a. Microcoulomb
b. Coulomb
c. Alpha particle
d. Electron charge

Correct answer: d. Electron charge

Explanation:
Electron charge is the smallest unit of charge.

MCQs No. 76

Capacitance of parallel plate capacitor:

a. dε₀/A
b. Aε₀/d
c. A/dε₀
d. d/Aε₀

Correct answer: b. Aε₀/d

Explanation:
Formula of parallel plate capacitor: C = ε₀A/d.

MCQs No. 77

Capacitance does NOT depend on:

a. Plate distance
b. Area
c. Electric field
d. Medium

Correct answer: c. Electric field

Explanation:
Capacitance depends only on geometry and medium.

MCQs No. 78

Work done on equipotential surface is:

a. Positive
b. Infinite
c. Negative
d. Zero

Correct answer: d. Zero

Explanation:
Potential difference is zero, so W = qΔV = 0.

MCQs No. 79

Potential barrier of silicon diode is:

a. 0.3 V
b. 0.7 V
c. 3 V
d. 7 V

Correct answer: b. 0.7 V

Explanation:
Standard barrier potential of silicon diode is 0.7 V.

MCQ 80
In silicon diode, $V_B = 0.7 \, \text{V}$ . Conversion of A.C into D.C is called:
A) Modulation
B) Amplification
C) Oscillation
D) Rectification

Answer: D) Rectification
Explanation: Rectification is the process of converting alternating current (A.C) into direct current (D.C).

MCQ 81
In a common-emitter amplifier, the phase difference between input signal voltage and output signal voltage is:
A) $\frac{\pi}{4}$
B) $\pi$
C) 0
D) $\frac{\pi}{2}$

Answer: B) $\pi$
Explanation: In a common-emitter amplifier, the output is inverted, giving a phase difference of $\pi$ (180°) between input and output.

MCQ 82
A.C. can be converted into D.C. by:
A) Transformer
B) Rectifier
C) Motor
D) Capacitor

Answer: B) Rectifier
Explanation: A rectifier is an electrical device used to convert A.C. into D.C.

MCQ 83
A diode characteristic curve is plotted between:
A) Voltage and time
B) Forward voltage and reverse voltage
C) Voltage and current
D) None of the above

Answer: C) Voltage and current
Explanation: Diode characteristic curves show the relationship between voltage applied across the diode and the resulting current.

MCQ 84
Output resistance of an op-amp is:
A) High
B) Zero
C) Low
D) Equal to input resistance

Answer: C) Low
Explanation: The output resistance of an ideal op-amp is low to allow maximum voltage delivery to the load.

MCQ 85
Which diode works under reverse bias?
A) LED
B) Photovoltaic cell
C) Photodiode
D) Silicon diode

Answer: C) Photodiode
Explanation: Photodiodes operate in reverse bias to detect light, generating current proportional to light intensity.

MCQ 86
Logic gates can control some physical parameters like:
A) Temperature
B) Resistance
C) Capacitance
D) Current

Answer: A) Temperature
Explanation: Certain logic gates in sensors or control circuits can be used to regulate physical parameters such as temperature.

MCQ 87
Voltage gain of the common-emitter NPN transistor as an amplifier is:

A) $\beta \frac{r_{ic}}{R_c}$

B) $\beta \frac{I_e}{R_c}$

C) $\beta \frac{V_c}{R_c}$

D) $\beta \frac{R_c}{r_{ie}}$

Answer: D) $\beta \frac{R_c}{r_{ie}}$
Explanation: The voltage gain of a common-emitter amplifier is $A_v = -\beta \frac{R_c}{r_{ie}}$ .

MCQ 88
In forward biasing, the value of diode resistance is:
A) Large
B) Very large
C) Small
D) Very small

Answer: C) Small
Explanation: Forward-biased diodes offer minimal resistance due to the narrowing of the depletion region.

MCQ 89
In which type of logic gate is the output one when both inputs are zero?
A) NOT gate
B) NOR gate
C) OR gate
D) AND gate

Answer: B) NOR gate
Explanation: A NOR gate outputs 1 only when all its inputs are 0.

MCQ 90
Find the gain of an inverting amplifier with external resistance $R_2 = 100 \, k\Omega$ and $R_1 = 10 \, k\Omega$ :
A) -5
B) -10
C) -2
D) 50

Answer: B) -10
Explanation: Gain of inverting amplifier: $G = -\frac{R_2}{R_1} = -\frac{100k}{10k} = -10$ .

MCQ 91

In a photovoltaic cell, current is directly proportional to:
A) Wavelength of light
B) Intensity of light
C) Frequency of light
D) Energy

Answer: B) Intensity of light
Explanation: The photocurrent in a photovoltaic cell increases with light intensity.

MCQ 92
Which factor does not affect the conductivity of a PN-junction diode?
A) Doping
B) Temperature
C) Voltage
D) Pressure

Answer: D) Pressure
Explanation: Conductivity depends on doping, temperature, and applied voltage, but not on pressure.

MCQ 93
Expression for current gain ( $\beta$ ) of a transistor is:

A) $\beta = \frac{I_B}{I_C}$

B) $\beta = I_B + I_C$

C) $\beta = I_C - I_B$

D) $\beta = \frac{I_C}{I_B}$

Answer: D) $\beta = \frac{I_C}{I_B}$
Explanation: Current gain $\beta$ is the ratio of collector current to base current.

MCQ 94
Electric field at a point inside a uniformly charged sphere is:
A) Uniform
B) Variable
C) Zero
D) Stronger

Answer: C) Zero
Explanation: Inside a uniformly charged sphere, electric field is zero (by Gauss’s law).

MCQ 95
Boolean expression $X = A \cdot B$ corresponds to which gate?
A) NAND gate
B) NOR gate
C) OR gate
D) AND gate

Answer: D) AND gate
Explanation: $X = A \cdot B$ is the AND operation.

MCQ 96
Potential barrier for germanium at room temperature is:
A) 0.3 V
B) 0.5 V
C) 0.7 V
D) 0.9 V

Answer: A) 0.3 V
Explanation: Ge diode has a potential barrier of 0.3 V.

MCQ 97
Input resistance of an op-amp is:
A) Zero
B) Low
C) High
D) Equal to output resistance

Answer: C) High
Explanation: Op-amps have very high input resistance to avoid loading the source.

MCQ 98
The resistance between the inverting (-) and non-inverting (+) inputs of an op-amp is of the order of:
A) Ohms
B) Kilo Ohms
C) Thousands Ohms
D) Mega Ohms

Answer: D) Mega Ohms
Explanation: The differential input resistance is very high, typically in Mega Ohms.

MCQ 99
LEDs are made from which semiconductor?
A) Silicon
B) Germanium
C) Carbon
D) Gallium arsenide

Answer: D) Gallium arsenide
Explanation: LEDs use GaAs or GaAsP because their energy gaps emit visible light.

MCQ 100
Two charges of $10 μ C$ and $14.4 μ C$ are 12 cm apart. The force between them is:
A) 10 N
B) 90 N
C) $9 \times 10^5\,\text{N}$
D) $9 \times 10^7\,\text{N}$

Answer: A) 10 N
Explanation: Using Coulomb’s law: $F = k \frac{q_1 q_2}{r^2} = 10\,\text{N}$ .

MCQ 101
The open loop gain of an amplifier is of the order of:
A) 10
B) 100
C) 1000
D) $10^5$

Answer: D) $10^5$
Explanation: Typical op-amp open-loop gain is very high, around $10^5$

MCQ 102
The truth table of a logic function:
A) Summarizes its output values
B) Tabulates all its input conditions only
C) Displays all its input/output possibilities
D) Is not based on logic gates

Answer: C) Displays all its input/output possibilities
Explanation: A truth table shows every possible combination of inputs and corresponding outputs.

MCQ 103
The colour of light emitted by an LED depends on:
A) Its forward biasing
B) Type of semiconductor material used
C) Amount of forward current
D) Its reverse biasing

Answer: B) Type of semiconductor material used
Explanation: The energy gap of the semiconductor determines the wavelength (color) of emitted light.

MCQ 104
In a comparator circuit, when intensity of light decreases, the resistance of LDR:
A) Increases
B) Decreases
C) Voltage decreases
D) Voltage increases

Answer: A) Increases
Explanation: LDR resistance is inversely proportional to light intensity; less light → higher resistance.

MCQ 105
The term inverter is used for which logic gate?
A) NOR
B) NAND
C) XNOR
D) NOT

Answer: D) NOT
Explanation: A NOT gate inverts the input signal; hence called an inverter.

MCQ 106
When two capacitors of equal capacitance $C$ are connected in series, their effective capacitance is $C_s$ . If connected in parallel, effective capacitance becomes $C_p$ . Then $C_s : C_p$ is:
A) 2:1
B) 1:2
C) 4:1
D) 1:4

Answer: D) 1:4
Explanation: Series: $C_s = C/2$ ; Parallel: $C_p = 2C$ ; hence $C_s : C_p = 1:4$ .

MCQ 107
The negative of potential gradient is called:
A) Electric potential
B) Electric intensity
C) Electric energy
D) Electric flux

Answer: B) Electric intensity
Explanation: $E = -\frac{\Delta V}{\Delta r}$ defines electric field intensity.

MCQ 108
Boolean equation for XOR gate is:
A) $X = A \cdot B + B \cdot A$
B) $\overline{X} = A \cdot \overline{B} + \overline{A} \cdot B$
C) $X = \overline{A} + \overline{B} + A \cdot B$
D) $X = \overline{A \cdot B + B \cdot A}$

Answer: B) $\overline{X} = A \cdot \overline{B} + \overline{A} \cdot B$
Explanation: XOR outputs 1 when inputs are different; its complement is given above.

MCQ 109
A potential barrier of 0.7 V exists across a PN junction made from:
A) Silicon
B) Germanium
C) Indium
D) Gallium

Answer: A) Silicon
Explanation: Si diode forward voltage ≈ 0.7 V.

MCQ 110
Photodiode is not used in:
A) Photovoltaic cell
B) Automatic switching
C) Detection of light
D) Logic circuits

Answer: A) Photovoltaic cell
Explanation: Photodiodes are mainly used for sensing, not power generation.

MCQ 111
Photovoltaic cell is made from:
A) Arsenic
B) Carbon
C) Germanium
D) Silicon

Answer: D) Silicon
Explanation: Silicon absorbs photons and generates electricity.

MCQ 112
Minimum number of semiconductor diodes required for full-wave rectification:
A) 1
B) 2
C) 3
D) 4

Answer: B) 2
Explanation: Full-wave rectifier requires two diodes with a center-tapped transformer.

MCQ 113
AC is converted into DC by:
A) Capacitor
B) Inductor
C) Transistor
D) Diode

Answer: D) Diode
Explanation: Diode allows current in only one direction → rectification.

MCQ 114
Gain of an inverting amplifier is given by:
A) $1 + \frac{R_2}{D}$
B) $1 + \frac{R_1}{R_+}$
C) $-\frac{R_2}{R_1}$
D) $\frac{R_1}{R_2}$

Answer: C) $-\frac{R_2}{R_1}$
Explanation: Inverting amplifier gain = - (feedback resistor / input resistor).

MCQ 115
Which one is not a fundamental logic gate?
A) OR
B) AND
C) NOT
D) NAND

Answer: D) NAND
Explanation: Fundamental gates are OR, AND, NOT; NAND is a universal gate.

MCQ 116
If a positive charge is moved against the electric field, it gains:
A) P.E.
B) K.E.
C) Mechanical energy
D) Electrical potential energy

Answer: D) Electrical potential energy
Explanation: Work done against the field is stored as electrical potential energy.

MCQ 117
Selenium is a conductor in:
A) Dark
B) Light
C) Heat
D) Toner

Answer: B) Light
Explanation: Selenium is photoconductive; conducts when exposed to light.

MCQ 118
Greater concentration of impurity is added in:
A) Base
B) Emitter
C) Collector
D) LED

Answer: B) Emitter
Explanation: Emitter is heavily doped; base lightly doped; collector intermediate.

MCQ 119
If the distance between two charges is doubled, the force between them:
A) Becomes 4 times
B) Becomes 2 times
C) Becomes 1/4 times
D) Becomes 1/2 times

Answer: C) Becomes 1/4 times
Explanation: Coulomb’s law: $F \propto 1/r^2$ .

MCQ 120
Three capacitors of 2 μF each are connected to get 3 μF equivalent capacitance. Connection type:
A) Three in series
B) Three in parallel
C) Two in series, one in parallel
D) Two in parallel, one in series

Answer: C) Two in series, one in parallel
Explanation: Effective capacitance can be calculated using series-parallel combination formula.

MCQ 121
Selenium is a:
A) Conductor
B) Insulator
C) Photoconductor
D) Semiconductor

Answer: C) Photoconductor
Explanation: Selenium is an insulator in darkness and conducts when exposed to light.

MCQ 122
The electron volt (eV) is the unit of:
A) Electric current
B) Electric energy
C) Electric potential
D) Potential difference

Answer: B) Electric energy
Explanation: 1 eV = energy gained by an electron moving through a potential difference of 1 volt.

MCQ 123
Electrostatics is the study of:
A) Electromagnetism
B) Electric charges at rest
C) Magnetic induction
D) Electric field

Answer: B) Electric charges at rest
Explanation: Electrostatics deals with stationary charges and forces between them.

MCQ 124
If the distance between two charges is halved and the charges are doubled, the force between them becomes:
A) 2 times
B) 4 times
C) 8 times
D) 16 times

Answer: D) 16 times
Explanation: $F \propto q_1 q_2 / r^2$ ; doubling q’s and halving distance: $F' = 4 / (1/4) = 16 F$ .

MCQ 125
If the magnitude of charges is doubled and the distance between them is also doubled, the Coulomb force:
A) Doubles
B) Halves
C) Remains same
D) Quadruples

Answer: C) Remains same
Explanation: $F \propto (2q \cdot 2q) / (2r)^2 = 4 / 4 = F$ .

MCQ 126
Electric flux is expressed as:
A) $\Phi_e = \vec{E} \times \vec{A}$
B) $\Phi_e = \vec{F} \cdot \vec{Q}$
C) $\Phi_e = \vec{E} \cdot \vec{A}$
D) $\Phi_e = \vec{E} A^2$

Answer: C) $\Phi_e = \vec{E} \cdot \vec{A}$
Explanation: Electric flux = dot product of electric field and area vector.

MCQ 127
A charge of $10^{-10}$ C between two parallel plates 1 cm apart experiences a force of $10^{-5}$ N. The potential difference between the plates is:
A) 10 V
B) $10^2$ V
C) $10^3$ V
D) $10^4$ V

Answer: C) $10^3$ V
Explanation: $E = F/q = 10^{-5}/10^{-10} = 10^5 \, N/C$ ; $\Delta V = E \cdot d = 10^5 \cdot 0.01 = 10^3$ .

MCQ 128
One billion electrons are added to a pith ball. Its charge is:
A) $-1.6 \times 10^{-10}$ C
B) $-1.6 \times 10^{-12}$ C
C) $-1.6 \times 10^{-14}$ C
D) $-1.6 \times 10^{-7}$ C

Answer: A) $-1.6 \times 10^{-10}$ C
Explanation: $Q = n e = 10^9 \cdot (-1.6 \times 10^{-19}) = -1.6 \times 10^{-10}$ .

MCQ 129
Which of the following is not a statement of electric flux?
A) The effect of $\vec{E}$
B) Number of field lines through an area
C) Scalar product of E and A
D) Vector product of E and A

Answer: A) The effect of $\vec{E}$
Explanation: Electric flux is defined mathematically as dot product; “effect of E” is not precise.

MCQ 130
Gauss’s law can only be applied to:
A) Curved surface
B) Flat surface
C) Any surface
D) Closed surface

Answer: D) Closed surface
Explanation: Gauss’s law applies to total flux through a closed surface enclosing charges.

MCQ 131
Intensity of field inside a hollow charged sphere is:
A) Negative
B) Unaffected
C) Zero
D) Maximum

Answer: C) Zero
Explanation: Electric field inside a conductor in electrostatic equilibrium is zero.

MCQ 132
In a photocopier, the drum is coated with:
A) Copper
B) Silver
C) Selenium
D) Gold

Answer: C) Selenium
Explanation: Selenium is photoconductive and is used in photocopying.

MCQ 133
If electric lines of force are equally spaced, the electric field is:
A) Uniform
B) Non-uniform
C) Weak
D) Strong

Answer: A) Uniform
Explanation: Equally spaced field lines indicate a uniform electric field.

MCQ 134
Electric field created by a positive point charge is:
A) Radially inward
B) Zero
C) Circular
D) Radially outward

Answer: D) Radially outward
Explanation: Field lines emanate outward from positive charges.

MCQ 135
The net charge on a capacitor (each plate magnitude q) is:
A) Infinity
B) 2q
C) q/2
D) Zero

Answer: D) Zero
Explanation: Plates carry +q and -q → net charge = 0.

MCQ 136
Electron volt (eV) is the unit of:
A) Electric current
B) Electric energy
C) Potential
D) Potential difference

Answer: B) Electric energy
Explanation: Energy gained by one electron moving through 1 V potential difference.

MCQ 137
S.I. unit of electric flux is:
A) N·m·C⁻¹
B) N·m²·C⁻¹
C) N·m²·C
D) N·m

Answer: B) N·m²·C⁻¹
Explanation: From $\Phi_e = E \cdot A$ , units: $(N/C)·m² = N·m²·C⁻¹$ .

MCQ 138
If separation between capacitor plates is doubled, capacitance becomes:
A) Double
B) Half
C) One fourth
D) Three times

Answer: B) Half
Explanation: $C = \varepsilon_0 A / d \propto 1/d$ .

MCQ 139
Absolute potential at 20 cm from a charge 2 μC:
A) $9 \times 10^2$ V
B) $9 \times 10^3$ V
C) $9 \times 10^4$ V
D) $9 \times 10^5$ V

Answer: C) $9 \times 10^4$ V
Explanation: $V = Kq/r = 9 \times 10^9 \cdot 2 \times 10^{-6}/0.2 = 9 \times 10^4$ V.

MCQ 140. Equipotential surfaces:

a) Are always planes
b) Have constant electric field
c) Are perpendicular to electric field
d) Are along electric field
Answer: c) Are perpendicular to electric field
Explanation: No work is done moving a charge along an equipotential; field is normal to surface.

MCQ 141. Electric field at a point on the axial line of a dipole is:

E = 0

E = 2 p / 4 π ϵ_{0} r^{3}

E = p / 4 π ϵ_{0} r^{3}

E = q / 4 π ϵ_{0} r^{2}

Answer: b)

E = 2 p / 4 π ϵ_{0} r^{3}

Explanation: Axial line field of dipole: double the equatorial line field.

MCQ 142. The electric field due to an infinite plane sheet of charge:
a) Decreases with distance
b) Increases with distance
c) Remains constant
d) Is zero
Answer: c) Remains constant
Explanation: Field from infinite sheet:

E = σ / 2 ϵ_{0}

, independent of distance.

MCQ 143. Electric potential at the centre of a uniformly charged ring is:
a) Zero
b)

k Q / R

k Q / R^{2}

d) Infinity
Answer: b)

k Q / R

Explanation: Potential is scalar; contributions from all elements add.

MCQ 144. Electric potential inside a hollow spherical conductor:
a) Zero
b) Same as on surface
c) Varies with radius
d) Infinite
Answer: b) Same as on surface
Explanation: Field inside is zero, so potential remains constant throughout.

MCQ 145. Two charges q and 2q are separated by distance r. Force on q in vacuum is F. If medium has εr = 2, new force is:
a) F/2
b) 2F
c) F
d) F/4
Answer: a) F/2
Explanation:

F_{medium} = F / ϵ_{r} = F / 2

MCQ 146. Electric field between two parallel plate capacitors (neglecting edge effect) is:
a) Zero
b)

E = σ / ϵ_{0}

c) Uniform
d) Decreases with distance
Answer: c) Uniform
Explanation: Field is uniform between large plates except near edges.

MCQ 147. The energy stored in a system of charges is:
a) Kinetic energy only
b) Potential energy only
c) Zero
d) Both kinetic and potential
Answer: b) Potential energy only
Explanation: Electrostatic energy is stored as potential energy due to charge configuration.

MCQ 148. Electric field inside a charged spherical shell is:
a) Maximum at center
b) Zero
c) Equal to surface field
d) Depends on shell thickness
Answer: b) Zero
Explanation: By Gauss’s law, field inside a shell is zero.

MCQ 149. If distance between two charges is doubled, the force between them becomes:
a) 2F
b) F/2
c) F/4
d) F/8
Answer: c) F/4
Explanation: Coulomb’s law:

F \propto 1 / r^{2}

MCQ 150. Electric potential is related to electric field by:
a)

V = E \cdot d

E = - d V / d r

E = V^{2}

V = E^{2} / 2

Answer: b)

E = - d V / d r

Explanation: Field is negative gradient of potential.

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150 High-Scoring MCQs on Electrostatics (Set-2 Basic to Expert Level MCQs)

150 Important MCQs (Set-2 of Basic to Expert Level MCQs) on Electrostatics, Physics (Unit-Wise MCQs Practice):

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