Electrostatic MDCAT MCQs 2025 PDF Download

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Electrostatic MDCAT MCQs for Students

Quick Quiz

The plates of a parallel plate capacitor each have an area of 100 cm² and are separated by a 1 mm gap. If mica with a dielectric constant of 6 is used between the plates, what is the radius of a sphere with the same capacitance?

a. 47.7 m

b. 4.77 m

c. 477 m

d. 0.47 m

Option b – 4.77 m

A number of capacitors rated at 4 µF, 250 V are available. What is the least number of such capacitors required to build a system with a total capacitance of 16 µF and a voltage rating of 1000 V?

a. 4

b. 16

c. 32

d. 64

Option d – 64

A charged conducting sphere of radius R is connected to an uncharged conducting sphere of radius 3R. How much charge will move between them?

a. 0.25 Q

b. 0.5 Q

c. 0.75 Q

d. 1.5 Q

Option c – 0.75 Q

A charged capacitor is disconnected from its battery, and a dielectric slab is inserted between the plates. What happens?

a. Charge reduces, voltage increases

b. Voltage drops, energy decreases, charge stays the same

c. Voltage increases, energy decreases, charge stays the same

d. None of the above

Option b – Voltage drops, energy decreases, charge stays the same

The capacitance of a spherical capacitor is 1 µF. If the separation between the spheres is 1 mm, what is the radius of the outer sphere?

a. 30 cm

b. 6 m

c. 9 cm

d. 3 m

Option d – 3 m

When a polythene sheet is placed between two charged parallel plates, the electric field becomes one-third. When a PVC slab is inserted, it becomes one-eighth. What is the ratio of their dielectric constants (PVC : Polythene)?

a. 3 : 8

b. 8 : 3

c. 5 : 8

d. 3 : 5

Option b – 8 : 3

What happens to the capacitance of a capacitor if a thin aluminum foil is placed between its plates?

a. It increases

b. It decreases

c. It stays the same

d. It becomes zero

Option c – It stays the same

An air capacitor has a capacitance of 18 µF. If the plate distance is tripled and a dielectric is inserted, the new capacitance becomes 72 µF. What is the dielectric constant of the material?

a. 4

b. 9

c. 12

d. 2

Option c – 12

Three capacitors each of 3 µF are connected in different ways. What are the maximum and minimum capacitances possible?

a. 9 µF, 1 µF

b. 8 µF, 2 µF

c. 9 µF, 0 µF

d. 3 µF, 2 µF

Option a – 9 µF, 1 µF

Among different capacitor combinations, which stores the highest energy for the same voltage?

a. Two in parallel and one in series

b. All three in series

c. All three in parallel

d. Two in series and one in parallel

Option c – All three in parallel

Capacitors of 20 µF and 30 µF are charged with 200 V and 100 V respectively. After connecting them, what is the common voltage?

a. 16 V

b. 140 V

c. 300 V

d. 400 V

Option b – 140 V

If k is dielectric constant and x is dielectric strength, which combination is best for capacitor materials?

a. High k, high x

b. High k, low x

c. Low k, low x

d. Low k, high x

Option a – High k, high x

A 20 µF capacitor charged to 10 V is connected to an uncharged 60 µF capacitor. How much energy is lost?

a. 250 J

b. 750 J

c. 125 J

d. 150 J

Option b – 750 J

Assertion: Energy in a capacitor decreases when the plate distance is increased after disconnection from the battery. Reason: Work must be done to separate the plates.

a. Both true, and reason explains assertion

b. Both true, but reason doesn’t explain assertion

c. Assertion true, reason false

d. Assertion false, reason true

Option d – Assertion false, reason true

What part of the energy provided by a battery is stored in a capacitor?

a. 75%

b. 100%

c. 25%

d. 50%

Option d – 50%

A 12 V battery is connected to a parallel plate capacitor. If the separation between the plates is tripled, what happens to stored energy?

a. Triples

b. Reduces to one-third

c. Remains constant

d. Reduces to one-ninth

Option b – Reduces to one-third

Identify the non-polar dielectric from the list below:

a. Ethyl alcohol

b. Benzene

c. Ammonia

d. Hydrochloric acid

Option b – Benzene

A technician combines two capacitors to obtain 3.2 µF, 4 µF, 16 µF, and 20 µF. What are their values?

a. 8 µF and 4 µF

b. 8 µF and 12 µF

c. 7 µF and 9 µF

d. 4 µF and 16 µF

Option d – 4 µF and 16 µF

A marble cube of side 2 m is placed in a 450 V/m electric field. If its dielectric constant is 2, what is the stored energy?

a. 2 µJ

b. 14 µJ

c. 20 µJ

d. 3.93 µJ

Option b – 14 µJ

What is the function of a Van de Graaff generator?

a. Produces high voltage

b. Accelerates particles like protons and deuterons

c. Used in nuclear physics

d. All of these

Option d – All of these

Capacitors are used in which circuits?

a. AC circuits

b. DC circuits

c. Both AC and DC

d. Neither AC nor DC

Option c – Both AC and DC

When an earthed uncharged conductor is placed near a charged conductor, what occurs?

a. Potential of charged conductor falls

b. Capacitance of charged conductor rises

c. Charge of charged conductor decreases

d. Both (a) and (b)

Option d – Both (a) and (b)

If one plate of a parallel plate capacitor is smaller than the other, what will be the charge on the smaller plate?

a. Less than the larger plate

b. More than the larger plate

c. Equal to the larger plate

d. Depends on the dielectric medium

Option c – Equal to the larger plate

If a positively charged body is connected to the earth, its potential becomes:

a) zero

b) infinity

c) positive

d) negative

Option a – zero

The Ohmic resistance of a capacitor for direct current is:

a) infinite

b) zero

c) 2Ω

d) 5Ω

Option a – infinite

In a uniform electric field, the lines of force are:

a) perpendicular to each other

b) parallel to each other

c) parallel to each other and equally spaced

d) carried

Option c – parallel to each other and equally spaced

The unit of capacitance is:

a) coulomb/volt

b) farad

c) ampere/volt

d) both a and b

Option d – both a and b

An arrangement that increases charge storing capacity without changing potential is called:

a) inductor

b) capacitor

c) resistor

d) transistor

Option b – capacitor

The ratio of the charge given to a conductor to its potential increase is called:

a) the capacity of the conductor

b) resistance of the conductor

c) the reactance of the conductor

d) the impedance of the conductor

Option a – the capacity of the conductor

An uncharged conductor is placed near a charged one. What changes?

a) both charge and potential remain constant

b) both charge and potential change

c) charge remains the same, potential decreases

d) charge remains the same, potential increases

Option c – charge remains the same, potential decreases

A capacitor charged using a 10 V battery holds 40 μC with air, and 100 μC with oil. The dielectric constant is:

a) 1.5

b) 2

c) 2.5

d) 5

Option c – 2.5

A 5 μF capacitor has a plate separation of 1 mm and 10 V potential. The force between the plates is:

a) 25 N

b) 0.5 N

c) 75 N

d) 0.25 N

Option b – 0.5 N

A 20 μF capacitor holds a charge of 10 mC. The potential difference is:

a) 500

b) 200

c) 50

d) 20

Option a – 500

64 drops of radius r and charge q combine. What is the charge on the larger drop?

a) q

b) 2q

c) 8q

d) 64q

Option d – 64q

When two charged conductors are connected, charge is shared:

a) equally

b) inversely with capacities

c) proportionally to capacities

d) both a and b

Option c – proportionally to capacities

Increasing the charge on a capacitor leads to:

a) more capacitance

b) more potential difference

c) less potential difference

d) no change in the field

Option b – more potential difference

The ratio of charge to potential in a body is called:

a) capacitance

b) conductance

c) induction

d) insulation

Option a – capacitance

A 4 μF capacitor charged to 400 V is connected with 10000 Ω resistance. Heat released is:

a) 0.64 J

b) 0.32 J

c) 0.16 J

d) 1.28 J

Option b – 0.32 J

Energy stored in a 1 μF capacitor charged to 1 kV is:

a) 5

b) 0.5

c) 0.005

d) 50

Option b – 0.5

Electric field between plates of a capacitor with dielectric:

a) decreases

b) increases

c) no change

d) either increases or decreases

Option a – decreases

A charged capacitor is disconnected and plates are moved apart. What happens?

a) charge becomes zero

b) capacitance becomes infinite

c) both charge and capacitance increase

d) potential difference increases

Option d – potential difference increases

The potential at the center of a charged conductor is:

a) zero

b) twice that on surface

c) half that on surface

d) equal to surface potential

Option d – equal to surface potential

What happens when the plates of a charged parallel plate capacitor are separated after disconnecting the battery?

a. The capacitor loses all its charge

b. Its capacitance becomes extremely high

c. The charge on the plates increases

d. The potential difference between the plates rises

Option d – The potential difference between the plates rises

A non-conducting sphere of radius R carries uniform charge distribution. What is true about the electric field at a distance r from the center?

a. r = R

b. For r < R, the field increases with distance

c. For r > R, the field decreases with distance

d. None of the above

Option b – For r < R, the field increases with distance

What happens to the electric field when a dielectric is inserted between the plates of a charged capacitor?

a. It decreases

b. It increases

c. It remains the same

d. None of these

Option a – It decreases

In which type(s) of electric circuits can capacitors be used?

a. Only in alternating current (AC) circuits

b. Only in direct current (DC) circuits

c. In both AC and DC circuits

d. In neither AC nor DC circuits

Option c – In both AC and DC circuits

If a dielectric slab is removed from a charged capacitor connected to a battery, what happens?

a. Some charge flows back to the battery

b. Additional charge is drawn from the battery

c. The voltage across the capacitor drops

d. No noticeable effect occurs

Option a – Some charge flows back to the battery

Assertion: Charge is a scalar quantity.

Reason: Charge remains unchanged with rotation or frame of reference.

a. Both assertion and reason are true, and the reason correctly explains the assertion

b. Both assertion and reason are true, but the reason does not explain the assertion

c. Assertion is true, but the reason is false

d. Assertion is false, but the reason is true

Option b – Both assertion and reason are true, but the reason does not explain the assertion

When 512 equal mercury drops combine to form a larger one, what is the ratio of the surface charge density of the big drop to each small drop?

a. 512 : 1

b. 1 : 8

c. 1 : 512

d. 8 : 1

Option d – 8 : 1

If three charges of equal magnitude q are placed at (0, -a, 0), (0, 0, 0), and (0, +a, 0), the equilibrium of the charge at origin is

a. Stable when displaced along Y-axis

b. Stable when displaced along Z-axis

c. Stable when displaced along X-axis

d. Stable in the XZ plane

Option a – Stable when displaced along Y-axis

Four charges of +2 µC each are placed at the corners of a square with 1 m sides. What is the force on the charge at corner B?

a. 0.04 N

b. 0.07 N

c. 0.14 N

d. 0.12 N

Option b – 0.07 N

Three charges are placed at the vertices of an equilateral triangle. Which is true regarding their equilibrium?

a. Equilibrium occurs if charges have equal magnitudes but not identical signs

b. Equilibrium occurs if all charges have the same sign but different magnitudes

c. Equilibrium occurs when the charges rotate about the triangle’s center

d. Electrostatic equilibrium is not possible in this setup

Option d – Electrostatic equilibrium is not possible in this setup

If the electric field at a distance x from a charge is E, what will be the field at 2x?

a. E/2

b. E/3

c. E/4

d. E/9

Option d – E/9

A flat circular plate has a 10 cm radius and a surface charge density of 6 μC/m². A 3 µC charge is placed 1 m away. What is the force on it?

a. 5 mN

b. 2.5 N

c. 6 N

d. 2 mN

Option a – 5 mN

Assertion: At a macroscopic level, electric charge appears continuous.

Reason: One coulomb contains around 10¹⁹ electrons.

a. Both assertion and reason are true, and the reason explains the assertion