Electric current, drift velocity, mobility and relation with current, Ohms law - Question Bank

1. A constant voltage is applied across a resistor. If the resistance of the resistor is decreased, the current flowing through it will:
A) Decrease
B) Increase
C) Remain unchanged
D) Become zero
2. Which of the following statements is INCORRECT regarding drift velocity?
A) It is the average velocity of charge carriers.
B) It is directly proportional to the applied electric field.
C) It is independent of the temperature of the conductor.
D) It is responsible for the electric current in a conductor.
3. The charge carriers in semiconductors (like Silicon) are:
A) Only electrons
B) Only holes
C) Electrons and holes
D) Free ions
4. The charge carriers in metals are:
A) Electrons
B) Protons
C) Ions
D) Holes
5. If the temperature of a semiconductor increases, its resistance:
A) Increases
B) Decreases
C) Remains the same
D) Becomes infinite
6. Which physical quantity is represented by the slope of the V-I graph for an ohmic conductor?
A) Current
B) Voltage
C) Resistance
D) Conductance
7. If two resistors R₁ and R₂ are connected in parallel, the equivalent resistance is:
A) R₁ + R₂
B) R₁ R₂ / (R₁ + R₂)
C) 1 / (R₁ + R₂)
D) (R₁ + R₂) / R₁ R₂
8. If two resistors R₁ and R₂ are connected in series, the equivalent resistance is:
A) R₁ + R₂
B) R₁ R₂ / (R₁ + R₂)
C) 1 / (R₁ + R₂)
D) (R₁ + R₂) / R₁ R₂
9. The resistance of a wire depends on:
A) Material, length, and temperature
B) Material, length, and area of cross-section
C) Material, temperature, and area of cross-section
D) Length, area of cross-section, and temperature
10. A wire carries a current of 1 A. If the electron density is 10²⁹ m⁻³ and the area of cross-section is 1 mm², what is the drift velocity of electrons? (e = 1.6 x 10⁻¹⁹ C)
A) 6.25 x 10⁻⁴ m/s
B) 6.25 x 10⁻³ m/s
C) 6.25 x 10⁻⁵ m/s
D) 6.25 x 10⁻² m/s
11. What is the definition of mobility (μ) in terms of drift velocity (v_d) and electric field (E)?
A) μ = v_d * E
B) μ = v_d / E
C) μ = E / v_d
D) μ = 1 / (v_d * E)
12. For a material that does not obey Ohm's law (non-ohmic), the V-I graph is:
A) Always a straight line
B) A curve
C) A circle
D) A constant value
13. If a resistor obeys Ohm's law, its V-I graph is a:
A) Parabola
B) Hyperbola
C) Straight line passing through the origin
D) Straight line not passing through the origin
14. Which of the following quantities is NOT a vector?
A) Electric field
B) Current density
C) Drift velocity
D) Electric current
15. Ohm's law is fundamentally a statement about the relationship between:
A) Voltage and charge
B) Current and resistance
C) Electric field and current density
D) Charge and time
16. If the relaxation time (τ) of electrons in a conductor decreases, the drift velocity for a given electric field will:
A) Increase
B) Decrease
C) Remain unchanged
D) Become zero
17. Drift velocity is directly proportional to relaxation time (τ) and electric field (E). The relation is:
A) v_d = E / (m τ)
B) v_d = m E / τ
C) v_d = e E τ / m
D) v_d = m τ / (e E)
18. The average time between successive collisions of electrons with the lattice ions in a conductor is called:
A) Relaxation time (τ)
B) Time period
C) Half-life
D) Time constant
19. In the equation J = σE, if the electric field E is doubled, the current density J becomes:
A) Half
B) The same
C) Double
D) Four times
20. If the current density (J) in a conductor is uniform and the area of cross-section is A, the total current I is given by:
A) I = J / A
B) I = J + A
C) I = J A
D) I = J - A
21. What is the unit of current density (J)?
A) A/m²
B) A·m
C) V/m
D) A/V
22. The drift velocity of electrons in a metal is typically of the order of:
A) 10⁻² m/s
B) 10⁻¹ m/s
C) 10⁻⁴ m/s
D) 10⁸ m/s
23. If the conductivity of a material is high, its resistivity is:
A) High
B) Low
C) Zero
D) Infinite
24. Conductivity (σ) is the reciprocal of:
A) Resistivity (ρ)
B) Resistance (R)
C) Mobility (μ)
D) Electric field (E)
25. Which statement best describes the microscopic form of Ohm's law?
A) J = σ E, where J is current density, σ is conductivity, and E is electric field.
B) V = IR, where V is voltage, I is current, and R is resistance.
C) I = n A v_d q, relating current to drift velocity.
D) μ = v_d / E, defining mobility.
26. A battery supplies a constant voltage of 12V to a resistor. If the resistance is 3 Ohms, what is the current?
A) 4 A
B) 36 A
C) 1 A
D) 0.25 A
27. What happens to the drift velocity of electrons in a wire if its cross-sectional area is increased, while the current remains the same?
A) It increases
B) It decreases
C) It remains the same
D) It becomes zero
28. If the temperature of a metallic conductor increases, its resistance:
A) Decreases
B) Increases
C) Remains the same
D) Becomes zero
29. The relation I = n A v_d q can be rewritten using v_d = μE and E = V/L as I = n A μ q (V/L). This implies that the resistance R is proportional to:
A) L / (n A μ q)
B) n A μ q / L
C) L / (n A)
D) A / (n L)
30. Ohm's law is not valid for:
A) Metallic conductors at constant temperature
B) Semiconductors
C) Electrolytic conductors
D) All of the above
31. If a material has very high electron mobility, it implies that:
A) It is a good insulator
B) Electrons can drift easily under a small electric field
C) It has very low conductivity
D) It requires a very large electric field to conduct electricity
32. Which factor does NOT affect the drift velocity of electrons in a conductor, assuming Ohm's law is obeyed?
A) Applied electric field
B) Mobility of electrons
C) Temperature of the conductor
D) The color of the conductor
33. If the length of a conductor is doubled while keeping the cross-sectional area and applied voltage constant, the drift velocity of electrons will:
A) Halve
B) Double
C) Remain the same
D) Become four times
34. Consider a conductor of length L and cross-sectional area A. If a voltage V is applied across its ends, the electric field E inside the conductor is approximately:
A) E = V L
B) E = L / V
C) E = V / L
D) E = V + L
35. The relationship between drift velocity (v_d) and electric field (E) is given by:
A) v_d = μ / E
B) v_d = E / μ
C) v_d = μ E
D) v_d = E + μ
36. A copper wire has a cross-sectional area of 1 mm². If the electron density in copper is 8.5 x 10²⁸ m⁻³, and the drift velocity is 0.5 mm/s, what is the current flowing through the wire? (Elementary charge e = 1.6 x 10⁻¹⁹ C)
A) 0.68 A
B) 1.36 A
C) 0.068 A
D) 6.8 A
37. If the number of free electrons per unit volume (n) in a conductor increases, and other factors remain constant, the current for a given drift velocity will:
A) Decrease
B) Increase
C) Remain unchanged
D) Become zero
38. Which of the following correctly relates electric current (I), drift velocity (v_d), charge carrier density (n), charge of carrier (q), and area of cross-section (A)?
A) I = n A v_d q
B) I = n v_d q / A
C) I = A v_d q / n
D) I = n A q / v_d
39. The SI unit of mobility is:
A) m/s
B) V/m
C) m/(V·s)
D) A·m/V
40. Mobility (μ) of charge carriers is defined as the ratio of:
A) Drift velocity to electric field
B) Electric field to drift velocity
C) Charge to electric field
D) Drift velocity to charge
41. The drift velocity (v_d) of charge carriers in a conductor is proportional to:
A) The resistance of the conductor
B) The temperature of the conductor
C) The applied electric field (E)
D) The length of the conductor
42. What is the direction of drift velocity of electrons in a conductor when an electric field is applied?
A) In the direction of the electric field
B) Opposite to the direction of the electric field
C) Perpendicular to the electric field
D) Random direction
43. Drift velocity is defined as:
A) The average velocity of free electrons in the absence of an electric field.
B) The average velocity with which free electrons get drifted under the influence of an external electric field.
C) The maximum velocity of any electron in a conductor.
D) The velocity of the electric field propagation.
44. If the voltage across a resistor is doubled, and the resistance remains constant, the current through the resistor will:
A) Halve
B) Remain the same
C) Double
D) Become four times
45. In Ohm's Law, the constant of proportionality between voltage (V) and current (I) is:
A) Conductance
B) Resistance
C) Resistivity
D) Mobility
46. What is Ohm's Law?
A) The current through a conductor is directly proportional to the voltage across its ends, provided temperature and other physical conditions remain unchanged.
B) The voltage across a conductor is directly proportional to the resistance, provided current remains unchanged.
C) The resistance of a conductor is directly proportional to the length and inversely proportional to the area of cross-section.
D) The power dissipated in a circuit is equal to the product of voltage and current.
47. A conductor carries a current of 2 Amperes. What is the amount of charge passing through a cross-section of the conductor in 5 seconds?
A) 2 Coulombs
B) 5 Coulombs
C) 10 Coulombs
D) 20 Coulombs
48. Which of the following represents the mathematical definition of electric current (I)?
A) I = V/R
B) I = Q/t
C) I = P/V
D) I = R/V
49. Electric current is defined as the rate of flow of:
A) Electric potential
B) Electric charge
C) Electric field
D) Electric resistance
50. What is the SI unit of electric current?
A) Volt
B) Ohm
C) Ampere
D) Watt
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