Electrostatics deals with the study of electric charges at rest. This chapter explains electric charge, types of charges, Coulomb’s law, electric field, electric potential, and capacitance. It also covers practical applications of electrostatics such as capacitors, photocopiers, and electrostatic painting. Understanding electrostatics is essential for grasping the basics of electricity and electronics.
1. The SI unit of electric charge is:
- A. Coulomb ✅
- B. Volt
- C. Ampere
- D. Ohm
Explanation: The coulomb (C) is the standard SI unit of electric charge.
2. Like charges:
- A. Attract each other
- B. Repel each other ✅
- C. Have no effect on each other
- D. Neutralize each other
Explanation: According to electrostatic principles, like charges repel while unlike charges attract.
3. Coulomb’s law states that the electrostatic force is directly proportional to:
- A. Product of charges ✅
- B. Sum of charges
- C. Difference of charges
- D. Square of charges
Explanation: F ∝ q₁ × q₂ and inversely proportional to the square of the distance between them.
4. The medium between two charges affects the force between them because of:
- A. Its density
- B. Its permittivity ✅
- C. Its temperature
- D. Its pressure
Explanation: The permittivity of a medium determines how much it reduces the electrostatic force compared to vacuum.
5. The region around a charged object where other charges feel a force is called:
- A. Magnetic field
- B. Electric field ✅
- C. Potential difference
- D. Capacitance
Explanation: An electric field exists around a charged body and exerts force on other charges within it.
6. The electric field lines for a positive charge point:
- A. Radially outward ✅
- B. Radially inward
- C. Circular around the charge
- D. Tangential to the surface
Explanation: Field lines originate from positive charges and terminate on negative charges.
7. Which of the following is used to store electric charge?
- A. Resistor
- B. Capacitor ✅
- C. Transformer
- D. Inductor
Explanation: Capacitors store electric charge and release it when needed in a circuit.
8. The unit of capacitance is:
- A. Volt
- B. Coulomb
- C. Farad ✅
- D. Ohm
Explanation: Capacitance is measured in farads (F), defined as 1 coulomb per volt.
9. In photocopiers, the electrostatic principle used is:
- A. Electromagnetic induction
- B. Attraction of toner particles to charged areas ✅
- C. Total internal reflection
- D. Diffraction
Explanation: Toner particles are charged and stick to oppositely charged areas of the drum to form images.
10. Which factor does NOT affect the capacitance of a parallel plate capacitor?
- A. Plate area
- B. Distance between plates
- C. Voltage applied ✅
- D. Dielectric constant
Explanation: Capacitance depends on geometry and dielectric material, not on applied voltage.
11. If two charges of +2 μC and -2 μC are separated, the force between them is:
- A. Repulsive
- B. Attractive ✅
- C. Zero
- D. Neutral
Explanation: Opposite charges always attract each other.
12. Which instrument is used to detect small electric charges?
- A. Ammeter
- B. Gold-leaf electroscope ✅
- C. Voltmeter
- D. Multimeter
Explanation: A gold-leaf electroscope is sensitive to small electric charges and indicates them by leaf divergence.
13. Which of these materials is a good insulator?
- A. Copper
- B. Rubber ✅
- C. Aluminum
- D. Iron
Explanation: Rubber does not allow free movement of charges, making it a good electrical insulator.
14. The process of transferring charge from one object to another by direct contact is called:
- A. Conduction ✅
- B. Induction
- C. Polarization
- D. Discharge
Explanation: In conduction, charges are transferred through direct contact between conductors.
15. Which dielectric material is commonly used in capacitors?
- A. Copper
- B. Mica ✅
- C. Iron
- D. Steel
Explanation: Mica is a good dielectric with high insulation strength, used in certain types of capacitors.