JEE Main - Electric current, drift velocity and mobility Online Test (MCQ Quiz)

1. What is the SI unit of electric current?

A) Volt B) Ampere C) Ohm D) Coulomb

2. Electric current is defined as the rate of flow of:

A) Potential difference B) Electric charge C) Electric field D) Magnetic field

3. If a charge of 10 Coulombs passes through a conductor in 2 seconds, what is the current?

A) 2 Amperes B) 5 Amperes C) 10 Amperes D) 20 Amperes

4. Which quantity is directly proportional to the electric current passing through a conductor?

A) Resistance B) Drift velocity C) Mobility D) Charge

5. What is drift velocity?

A) The random velocity of charge carriers B) The average velocity of charge carriers in a specific direction under an electric field C) The maximum velocity of charge carriers D) The velocity of light

6. In a metallic conductor, the charge carriers responsible for electric current are:

A) Electrons B) Protons C) Ions D) Neutrons

7. When an electric field is applied across a conductor, the free electrons:

A) Move randomly with increased speed B) Drift in a direction opposite to the electric field C) Drift in the same direction as the electric field D) Become stationary

8. The drift velocity of electrons in a conductor is generally:

A) Very high, of the order of 10^8 m/s B) Very low, of the order of 10^-4 m/s C) Comparable to the speed of light D) Zero

9. Mobility of charge carriers is defined as:

A) The ratio of drift velocity to electric field strength B) The product of drift velocity and electric field strength C) The inverse of drift velocity D) The inverse of electric field strength

10. The SI unit of mobility is:

A) m^2 V^-1 s^-1 B) m V^-1 s^-1 C) m^2 s^-1 D) V s^-1

11. Which of the following factors affects the drift velocity of electrons in a conductor?

A) Temperature B) Material of the conductor C) Length of the conductor D) All of the above

12. As temperature increases, the drift velocity of electrons in a conductor generally:

A) Increases B) Decreases C) Remains constant D) Becomes zero

13. The relationship between current (I), drift velocity (v_d), charge carrier density (n), and cross-sectional area (A) is given by:

A) I = n A v_d e B) I = n A v_d / e C) I = n e / (A v_d) D) I = A v_d / (n e)

14. In the formula I = n A v_d e, 'e' represents:

A) Electric field strength B) Charge of an electron C) Number of charge carriers D) Area of cross-section

15. If the drift velocity of electrons in a conductor doubles, and other factors remain constant, the current will:

A) Halve B) Double C) Remain the same D) Become four times

16. Mobility is a measure of how easily charge carriers can move under the influence of an electric field. Higher mobility means:

A) Slower movement of charge carriers B) Faster movement of charge carriers C) No movement of charge carriers D) Random movement of charge carriers

17. Which of the following has higher mobility of charge carriers?

A) Metals B) Semiconductors C) Insulators D) Vacuum

18. In a semiconductor, the charge carriers can be both electrons and holes. Their mobility values are generally:

A) Equal B) Different C) Zero D) Infinite

19. Ohm's law relates voltage, current, and resistance. It is a consequence of the microscopic description involving drift velocity when:

A) Temperature is not constant B) The conductor is non-ohmic C) The electric field is uniform and temperature is constant D) The conductor is very short

20. The average time interval between two successive collisions of electrons in a conductor is called:

A) Relaxation time B) Drift time C) Collision time D) Transit time

21. Drift velocity (v_d) is related to relaxation time (τ) and electric field (E) by the equation:

A) v_d = e E τ / m B) v_d = m E τ / e C) v_d = E τ / (m e) D) v_d = m τ / (e E)

22. In the equation v_d = e E τ / m, 'm' represents:

A) Mass of the electron B) Mobility C) Electric field D) Relaxation time

23. If the relaxation time of electrons in a conductor increases, the drift velocity will:

A) Decrease B) Increase C) Remain unchanged D) Become zero

24. A conductor has a current of 1.6 A. If the charge of an electron is 1.6 x 10^-19 C, how many electrons pass through a cross-section per second?

A) 10^19 B) 1.6 x 10^19 C) 10 D) 1.6

25. Consider a wire of length L and cross-sectional area A. If a voltage V is applied across its ends, the electric field E is approximately V/L. The drift velocity is proportional to:

A) V B) 1/L C) V/L D) L/V

26. The mobility of electrons in copper is approximately 4.3 x 10^-3 m^2 V^-1 s^-1. If an electric field of 10^-2 V/m is applied, what is the drift velocity?

A) 4.3 x 10^-5 m/s B) 4.3 x 10^-3 m/s C) 4.3 x 10^-1 m/s D) 4.3 x 10^-7 m/s

27. Which statement is INCORRECT regarding electric current?

A) It is the flow of charge. B) Its SI unit is Ampere. C) It is a scalar quantity. D) It is defined as the rate of flow of protons.

28. Drift velocity is a consequence of the interaction between charge carriers and the:

A) Applied electric field B) Atomic lattice of the conductor C) Magnetic field D) Both A and B

29. If the number density of charge carriers (n) in a conductor decreases, and drift velocity remains the same, the current will:

A) Increase B) Decrease C) Remain the same D) Become zero

30. The direction of conventional current is defined as the direction of flow of:

A) Electrons B) Positive charge C) Negative charge D) Holes

31. In most metallic conductors, the drift velocity of electrons is in the direction:

A) Of the applied electric field B) Opposite to the applied electric field C) Perpendicular to the applied electric field D) Random

32. Which of the following is NOT a factor determining mobility?

A) Mass of charge carrier B) Relaxation time C) Electric field strength D) Charge of the carrier

33. A current of 1 A flows through a wire. If the cross-sectional area is 1 mm^2 and the number density of electrons is 10^29 m^-3, calculate the drift velocity.

A) 10^-5 m/s B) 10^-4 m/s C) 10^-3 m/s D) 10^-2 m/s

34. The drift velocity of charge carriers in a conductor is directly proportional to the product of relaxation time and:

A) Charge carrier density B) Cross-sectional area C) Electric field strength D) Mass of charge carrier

35. Mobility is defined as the magnitude of drift velocity per unit:

A) Current B) Charge C) Electric field D) Resistance

36. In a conductor, the collisions of electrons with the lattice ions cause:

A) Increase in drift velocity B) Decrease in drift velocity C) Generation of heat D) Both B and C

37. Which material typically exhibits the highest mobility for its charge carriers?

A) Silicon B) Germanium C) Copper D) Gallium Arsenide

38. If the length of a conductor is doubled while keeping the voltage across it constant, the electric field strength:

A) Doubles B) Halves C) Remains the same D) Becomes zero

39. The relationship between drift velocity (v_d) and current (I) for a conductor of cross-sectional area A is:

A) I ∝ v_d B) I ∝ 1/v_d C) I ∝ sqrt(v_d) D) I ∝ v_d^2

40. Mobility of charge carriers in semiconductors is generally:

A) Higher than in metals B) Lower than in metals C) Equal to that in metals D) Zero

41. What happens to the drift velocity if the cross-sectional area of the conductor decreases, while current and charge carrier density remain constant?

A) Increases B) Decreases C) Remains the same D) Becomes zero

42. The relaxation time (τ) is inversely proportional to:

A) Temperature B) Electric field C) Charge carrier density D) Cross-sectional area

43. If the number of free electrons per unit volume in a conductor is 'n', the current density (J) is given by:

A) J = n e v_d B) J = n v_d / e C) J = e / (n v_d) D) J = v_d / (n e)

44. Which of the following statements about drift velocity is true?

A) It is the average speed of electrons between collisions. B) It is the net velocity of electrons in the direction of the electric field. C) It is always zero in a conductor. D) It increases with temperature.

45. Mobility of charge carriers is a property of the:

A) Electric field B) Voltage source C) Material of the conductor D) Geometry of the conductor

46. If a conductor carries a current of 0.5 A, and the drift velocity of electrons is 2.5 x 10^-4 m/s, what is the effective cross-sectional area if the electron density is 10^28 m^-3?

A) 10^-6 m^2 B) 10^-5 m^2 C) 10^-4 m^2 D) 10^-3 m^2

47. The drift velocity is directly proportional to the applied electric field (E) and the mobility (μ). This relationship is expressed as:

A) v_d = μ / E B) v_d = E / μ C) v_d = μ E D) v_d = E + μ

48. In a conductor, the mean free path of electrons is related to relaxation time and their average speed. A shorter mean free path implies:

A) Longer relaxation time B) Shorter relaxation time C) No change in relaxation time D) Zero relaxation time

49. Which of the following quantities is a vector?

A) Electric current B) Electric charge C) Drift velocity D) Mobility

50. If the temperature of a metallic conductor increases, the resistance increases because:

A) The number of free electrons increases B) The drift velocity of electrons increases C) The relaxation time of electrons decreases D) The mobility of electrons increases

Electric current, drift velocity and mobility - Online Test

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