NEET UG - Electric current, drift velocity, mobility and relation with current, Ohms law Online Test (MCQ Quiz)

1. What is the SI unit of electric current?

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

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

A) Electric potential B) Electric charge C) Electric field D) Electric resistance

3. 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

4. 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

5. 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.

6. In Ohm's Law, the constant of proportionality between voltage (V) and current (I) is:

A) Conductance B) Resistance C) Resistivity D) Mobility

7. 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

8. 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.

9. 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

10. 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

11. 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

12. The SI unit of mobility is:

A) m/s B) V/m C) m/(V·s) D) A·m/V

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. Ohm's law is not valid for:

A) Metallic conductors at constant temperature B) Semiconductors C) Electrolytic conductors D) All of the above

22. 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)

23. If the temperature of a metallic conductor increases, its resistance:

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

24. 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

25. 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

26. 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.

27. Conductivity (σ) is the reciprocal of:

A) Resistivity (ρ) B) Resistance (R) C) Mobility (μ) D) Electric field (E)

28. If the conductivity of a material is high, its resistivity is:

A) High B) Low C) Zero D) Infinite

29. 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

30. What is the unit of current density (J)?

A) A/m² B) A·m C) V/m D) A/V

31. 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

32. 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

33. 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

34. 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)

35. 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

36. 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

37. Which of the following quantities is NOT a vector?

A) Electric field B) Current density C) Drift velocity D) Electric current

38. 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

39. 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

40. 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)

41. 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

42. 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

43. 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

44. 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

45. 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

46. If the temperature of a semiconductor increases, its resistance:

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

47. The charge carriers in metals are:

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

48. The charge carriers in semiconductors (like Silicon) are:

A) Only electrons B) Only holes C) Electrons and holes D) Free ions

49. 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.

50. 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

Electric current, drift velocity, mobility and relation with current, Ohms law - Online Test

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