MCQs Physics chapter 1 electric charges and fields
MCQs Physics chapter 1 electric charges and fields
This chapter provides a comprehensive introduction to the fundamental principles of electrostatics, focusing primarily on the nature and behavior of electric charges. Through examples drawn from daily life, the author elucidates the properties of attraction and repulsion between charges and references the classification of positive and negative charges proposed by Benjamin Franklin. The text explains essential properties of charge—such as conservation, additivity, and quantization—demonstrating that charge is always an integral multiple of a specific fundamental unit. Coulomb's Law mathematically defines the force acting between two point charges, a concept subsequently extended to multi-charge systems through the Principle of Superposition. Furthermore, the text distinguishes between conductors and insulators, and describes instruments—such as the gold-leaf electroscope—used for detecting electric charge. Finally, through various examples, the electric force is compared with the gravitational force, thereby underscoring its immense significance within the realm of physics.
1. The word 'electricity' is coined from the Greek word 'elektron', which translates to:
A) Silk
B) Amber
C) Wool
D) Glass
Answer: B
2. By historical convention, what is the sign of the charge acquired by a glass rod when it is rubbed with silk?
A) Negative
B) Neutral
C) Positive
D) Variable
Answer: C
3. Which simple apparatus can be used to detect the presence of an electric charge on a body?
A) Torsion balance
B) Voltmeter
C) Gold-leaf electroscope
D) Ammeter
Answer: C
4. When a neutral solid body is electrified by rubbing, the charge is acquired primarily through the transfer of:
A) Protons
B) Neutrons
C) Atoms
D) Electrons
Answer: D
5. Materials like glass, plastic, and nylon that offer high resistance to the passage of electricity are classified as:
A) Conductors
B) Semiconductors
C) Insulators
D) Superconductors
Answer: C
6. Which of the following is NOT one of the basic properties of electric charge?
A) Additivity
B) Quantisation
C) Conservation
D) Directionality
Answer: D
7. The fact that electric charge is always an integral multiple of a basic unit ($e$) was experimentally demonstrated in 1912 by:
A) Michael Faraday
B) Benjamin Franklin
C) Robert Millikan
D) Charles Coulomb
Answer: C
8. Approximately how many electrons are contained in a charge of –1 Coulomb?
A) $1.6 \times 10^{-19}$
B) $6 \times 10^{18}$
C) $9 \times 10^9$
D) $6.02 \times 10^{23}$
Answer: B
9. If $10^9$ electrons move out of a body to another body every second, approximately how much time is required to accumulate a total charge of 1 C?
A) 2 years
B) 20 years
C) 200 years
D) 2000 years
Answer: C
10. What device did Charles Coulomb use to measure the electrostatic force between two charged metallic spheres?
A) Gold-leaf electroscope
B) Spring balance
C) Torsion balance
D) Beam balance
Answer: C
11. In the SI system, the approximate value of the proportionality constant $k$ ($1/4\pi\epsilon_0$) in Coulomb's law is:
A) $8.854 \times 10^{-12} \text{ N m}^2\text{C}^{-2}$
B) $1.602 \times 10^{-19} \text{ N m}^2\text{C}^{-2}$
C) $9 \times 10^9 \text{ N m}^2\text{C}^{-2}$
D) $1 \text{ N m}^2\text{C}^{-2}$
Answer: C
12. The rule stating that the total force on any given charge is the vector sum of all the forces exerted on it by individual charges is known as:
A) Coulomb's Law
B) The principle of superposition
C) Gauss's Law
D) The law of conservation of charge
Answer: B
13. The SI unit for the electric field is:
A) Coulomb (C)
B) Newton (N)
C) Newton per Coulomb (N/C)
D) Coulomb per Newton (C/N)
Answer: C
14. For a point source exhibiting a positive charge, the electric field lines are directed:
A) Radially inwards
B) Radially outwards
C) In parallel straight lines
D) In concentric circles
Answer: B
15. If an electron and a proton fall through the same distance in an identical uniform electric field (ignoring gravity), how do their times of fall compare?
A) The electron takes a greater time.
B) The proton takes a greater time.
C) Both take the exact same time.
D) The time of fall is zero.
Answer: B
16. Which of the following is a correct characteristic of electrostatic field lines?
A) They form closed loops.
B) They can intersect each other at exactly one point.
C) They start from negative charges and end at positive charges.
D) They are continuous curves without any breaks in a charge-free region.
Answer: D
17. Electric flux $\Delta\phi$ through an area element $\Delta S$ is mathematically defined as:
A) $E + \Delta S$
B) $E / \Delta S$
C) $E \cdot \Delta S$
D) $E \times \Delta S$
Answer: C
18. By convention, the direction of the electric dipole moment vector $\mathbf{p}$ is:
A) From the positive charge to the negative charge
B) From the negative charge to the positive charge
C) Perpendicular to the axis connecting the charges
D) Outward from the center in all directions
Answer: B
19. At a distance $r$ that is much larger than the separation between the charges of a dipole ($r \gg a$), the electric field falls off as:
A) $1/r$
B) $1/r^2$
C) $1/r^3$
D) $1/r^4$
Answer: C
20. Molecules that possess a permanent electric dipole moment even in the absence of an external electric field (such as water) are called:
A) Non-polar molecules
B) Polar molecules
C) Neutral molecules
D) Insulating molecules
Answer: B
21. When a permanent electric dipole is placed in a uniform external electric field, the net force acting on the dipole is:
A) $qE$
B) $2qE$
C) Zero
D) Dependent on its orientation angle
Answer: C
22. The magnitude of the torque ($\tau$) experienced by a dipole with moment $p$ in a uniform electric field $E$ at an angle $\theta$ is given by:
A) $pE \cos\theta$
B) $pE \sin\theta$
C) $p/E$
D) $p + E$
Answer: B
23. Why does a plastic comb rubbed through dry hair attract small pieces of uncharged paper?
A) The paper becomes positively charged by induction.
B) The comb polarises the paper and exerts a net force due to its non-uniform electric field.
C) The paper converts into a perfect conductor.
D) The comb creates a magnetic field.
Answer: B
24. The SI unit of surface charge density ($\sigma$) is:
A) C/m
B) $\text{C/m}^3$
C) $\text{C/m}^2$
D) C
Answer: C
25. Gauss's law states that the total electric flux through any closed surface is equal to the total charge enclosed by the surface multiplied by:
A) $\epsilon_0$
B) $1/\epsilon_0$
C) $4\pi\epsilon_0$
D) $1/4\pi\epsilon_0$
Answer: B
26. When choosing a Gaussian surface to evaluate an electric field, what must be carefully avoided?
A) The surface passing through a continuous charge distribution
B) Choosing a spherical or cylindrical shape
C) The surface passing through any discrete point charge
D) Choosing a surface that encloses zero net charge
Answer: C
27. The magnitude of the electric field produced by an infinitely long thin straight wire with uniform linear charge density $\lambda$ is proportional to:
A) $1/r^2$
B) $1/r$
C) $r$
D) $1/r^3$
Answer: B
28. The electric field $E$ created by a uniformly charged infinite plane sheet with surface charge density $\sigma$ is:
A) $\sigma / \epsilon_0$
B) $\sigma / (2\epsilon_0)$
C) $2\sigma / \epsilon_0$
D) $\sigma \epsilon_0 / 2$
Answer: B
29. What is the electric field at all points inside a uniformly charged thin spherical shell?
A) $q / (4\pi\epsilon_0 r^2)$
B) $q / (4\pi\epsilon_0 R^2)$
C) Zero
D) Dependent on the radius $r$
Answer: C
30. What happens when an electrified glass rod is brought into direct contact with the silk cloth it was originally rubbed against?
A) They repel each other strongly.
B) They attract each other more strongly than before.
C) They no longer attract or repel each other as their unlike charges nullify each other's effect.
D) Their electric charges double in magnitude.
Answer: C
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