NEETAceToday's NEET Daily

V-I characteristics of ohmic and non-ohmic conductors: NEET MCQs with answers

49 questions on this topic of Current Electricity (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

Practise Current Electricity freeAll Current Electricity questions

Free with a Google sign-in; NEET Daily needs no sign-in at all.

easy

1. Which of the following conditions is fundamentally required for a metallic conductor to exhibit a strictly linear V-I relationship as stated by Ohm's law?

  1. The electric field inside the conductor must vary inversely with drift speed.
  2. The potential difference applied must always exceed the work function of the metal.
  3. The conductor must have zero free-electron concentration at absolute zero.
  4. Physical conditions like temperature and mechanical strain must remain strictly constant.
Show answer and explanation

Answer: (D) Physical conditions like temperature and mechanical strain must remain strictly constant.

Ohm's law holds true for metallic conductors only when their physical conditions, such as temperature, dimensions, and mechanical strain, remain constant. If temperature changes, the relaxation time of electrons changes, causing the resistance to vary and leading to a non-linear V-I response.

medium

2. An electric component has a current-voltage relation given by I = 0.5 V², where V is in volts (V > 0) and I is in amperes. What is the dynamic resistance of this component when the operating potential difference is 4 V?

  1. 0.25 Ω
  2. 0.5 Ω
  3. 1.0 Ω
  4. 2.0 Ω
Show answer and explanation

Answer: (A) 0.25 Ω

From the given equation I = 0.5 V², differentiating with respect to V gives dI/dV = 2(0.5) V = V. Dynamic resistance r is the reciprocal, r = dV/dI = 1/V. Substituting V = 4 V yields r = 1/4 = 0.25 Ω.

hard

3. Two non-ohmic components X and Y are connected in series. The voltage drops across them depend on the common current I as V_X = 4 I² and V_Y = 6 I. What is the total dynamic resistance of the series combination when the current flowing through them is 1.5 A?

  1. 15 Ω
  2. 24 Ω
  3. 18 Ω
  4. 12 Ω
Show answer and explanation

Answer: (C) 18 Ω

The total voltage across the combination is V = V_X + V_Y = 4 I² + 6 I. The total dynamic resistance is r_d = dV/dI = d/dI (4 I² + 6 I) = 8 I + 6. Substituting I = 1.5 A gives r_d = 8(1.5) + 6 = 12 + 6 = 18 Ω.

medium

4. Consider the following statements regarding the V-I characteristics of devices: Statement I: An electrolyte solution can show deviation from Ohm's law at high potential gradients due to complete dissociation and saturation of ion drift. Statement II: Ohm's law is a fundamental law of nature like Newton's gravitational law.

  1. Both Statement I and Statement II are correct.
  2. Statement I is correct but Statement II is incorrect.
  3. Statement I is incorrect but Statement II is correct.
  4. Both Statement I and Statement II are incorrect.
Show answer and explanation

Answer: (B) Statement I is correct but Statement II is incorrect.

Statement I is correct; electrolytes and gases exhibit non-linearities at extreme electric fields. Statement II is incorrect because Ohm's law is an empirical relationship obeyed only by certain materials under specific physical conditions, not a fundamental universal law of nature.

easy

5. According to NCERT, which of the following is NOT one of the three main ways that conductors can deviate from Ohm's law?

  1. The resistance always drops strictly to zero whenever the applied electric field exceeds a critical value
  2. The relation between V and I depends on the sign of V for the same absolute value
  3. The relation between V and I is non-unique, such that there is more than one value of V for a given current I
  4. V ceases to be directly proportional to I as current increases
Show answer and explanation

Answer: (A) The resistance always drops strictly to zero whenever the applied electric field exceeds a critical value

NCERT classifies the limitations of Ohm's law into three categories: (a) V ceases to be proportional to I (e.g., heating of a metallic wire), (b) The relation between V and I depends on the sign of V (e.g., diode), and (c) The relation between V and I is not unique, i.e., there is more than one value of V for the same current I (e.g., GaAs). Resistance dropping strictly to zero is superconductivity at critical temperatures, not a general limitation outlined for normal non-ohmic behavior.

hard

6. A cylindrical conductor of length L and uniform area A is made of an ohmic material of resistivity ρ. If it is stretched isothermally so that its length increases by 10% while retaining uniform volume, the slope of its new I-V characteristic (with I on the vertical axis and V on the horizontal axis) compared to the initial slope S₀ will be:

  1. S₀ / 1.21
  2. 1.21 S₀
  3. S₀ / 1.10
  4. 1.10 S₀
Show answer and explanation

Answer: (A) S₀ / 1.21

For an ohmic conductor, the slope on an I-V plot is S = 1/R. Volume V = A·L is constant, so when L becomes 1.10 L, area A becomes A/1.10. New resistance R' = ρ(1.10 L)/(A/1.10) = 1.21 R₀. Therefore, the new slope is S' = 1/R' = 1/(1.21 R₀) = S₀ / 1.21.

medium

7. The dynamic resistance of a certain non-ohmic device varies with current I as r_d = dV/dI = α I², where α = 6.0 V A⁻³. When the current through the device is increased from 1.0 A to 2.0 A, the increase in potential difference ΔV across the device is:

  1. 21.0 V
  2. 18.0 V
  3. 7.0 V
  4. 14.0 V
Show answer and explanation

Answer: (D) 14.0 V

The change in potential difference is obtained by integrating the dynamic resistance with respect to current: ΔV = ∫ r_d dI = ∫ (6.0 I²) dI from I = 1.0 A to 2.0 A. Integrating gives ΔV = [2.0 I³] from 1 to 2 = 2.0 × (8 - 1) = 14.0 V.

medium

8. Statement I: A solar cell generates an electromotive force, and its I-V curve passes through quadrants other than the first quadrant when no external bias is applied. Statement II: An ideal ohmic conductor always has an I-V curve that passes through the origin (0, 0) and is symmetric under reversal of polarity of V.

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct

Statement I is correct; NCERT Figure 3.5(d) shows the I-V curve of a solar cell lying in the fourth quadrant because it delivers power rather than absorbing it. Statement II is correct because for an ideal ohmic conductor, I = V/R, meaning V = 0 gives I = 0, and reversing V simply reverses the sign of I symmetrically.

medium

9. Consider the following statements regarding the V-I characteristics of different materials: Statement A: In an ohmic conductor, the ratio V/I is independent of the value of V. Statement B: For a light-emitting diode (LED), the V-I curve is completely linear once conduction starts. Choose the correct option:

  1. Both Statement A and Statement B are correct.
  2. Statement A is correct, but Statement B is incorrect.
  3. Statement A is incorrect, but Statement B is correct.
  4. Both Statement A and Statement B are incorrect.
Show answer and explanation

Answer: (B) Statement A is correct, but Statement B is incorrect.

Statement A is correct because the resistance R = V/I is constant for an ohmic conductor. Statement B is incorrect because an LED is a semiconductor diode, and even beyond the threshold voltage, its V-I characteristic is exponential, making it non-linear and non-ohmic.

medium

10. A non-ohmic element satisfies the voltage-current relationship V = 8 I + 2 I², where V is in volts and I is in amperes. If the current through the element increases from 2 A to 4 A, the average dynamic resistance of the element over this interval is:

  1. 24 Ω
  2. 16 Ω
  3. 20 Ω
  4. 12 Ω
Show answer and explanation

Answer: (C) 20 Ω

The average dynamic resistance over the interval is ΔV/ΔI. At I₁ = 2 A: V₁ = 8(2) + 2(2)² = 16 + 8 = 24 V. At I₂ = 4 A: V₂ = 8(4) + 2(4)² = 32 + 32 = 64 V. Therefore, ΔV = 64 - 24 = 40 V, and ΔI = 4 - 2 = 2 A. Thus, R_avg = ΔV/ΔI = 40 / 2 = 20 Ω.

medium

11. In an experiment to study the V-I characteristics of a resistor, four readings of voltage (V in volts) and current (I in amperes) are recorded: (1.5, 0.30), (3.0, 0.60), (4.5, 0.88), (6.0, 1.15). What is the average dynamic resistance of this element between V = 3.0 V and V = 6.0 V?

  1. 5.00 Ω
  2. 4.80 Ω
  3. 5.45 Ω
  4. 5.22 Ω
Show answer and explanation

Answer: (C) 5.45 Ω

Dynamic resistance between 3.0 V and 6.0 V is given by ΔV / ΔI. Here, ΔV = 6.0 - 3.0 = 3.0 V, and ΔI = 1.15 - 0.60 = 0.55 A. Therefore, r_d = 3.0 / 0.55 ≈ 5.45 Ω.

medium

12. An electric discharge tube containing neon gas exhibits a voltage drop that falls from 120 V to 90 V when the current increases from 10 mA to 25 mA. The dynamic resistance of the gas discharge in this operating range is:

  1. +1200 Ω
  2. +2000 Ω
  3. -1200 Ω
  4. -2000 Ω
Show answer and explanation

Answer: (D) -2000 Ω

Dynamic resistance is r = ΔV / ΔI = (90 V - 120 V) / (25 × 10⁻³ A - 10 × 10⁻³ A) = -30 V / (15 × 10⁻³ A) = -2000 Ω. A negative value reflects a negative dynamic resistance region characteristic of gaseous discharges.

Keep going with Current Electricity. All 381 questions with instant answers, your mistakes saved for revision and your accuracy by topic.
Start practising

Other topics in Current Electricity