Electric Current & Ohm's Law — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Electric Current & Ohm's Law MCQs with step-by-step solutions (21 questions). Part of Current Electricity. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Electric Current & Ohm's Law · easy · theory
Electric current is defined as:
A. The charge stored per unit potential
B. The rate of flow of charge, and it is a scalar quantity ✓ Correct
C. The rate of flow of charge, and it is a vector quantity
D. The force per unit charge
Solution: $I = \dfrac{q}{t}$, measured in ampere. Although it has a direction of flow, current adds algebraically and is treated as a scalar.
Q2 — Electric Current & Ohm's Law · easy · theory
Ohm's law states that, at constant temperature:
A. The potential difference is independent of the current
B. The resistance is proportional to the current
C. The current through a conductor is proportional to the potential difference across it ✓ Correct
D. The current is proportional to the resistance
Solution: $V = IR$ holds only while the physical conditions, especially temperature, remain unchanged.
Q3 — Electric Current & Ohm's Law · easy · theory
The direction of conventional current in a metallic conductor is:
A. Opposite to the direction of electron flow ✓ Correct
B. Undefined
C. The same as the direction of electron flow
D. Perpendicular to the electron flow
Solution: Conventional current was defined as the flow of positive charge before the electron was discovered, so it runs opposite to the actual drift of electrons.
Q4 — Electric Current & Ohm's Law · medium · theory
The drift velocity of free electrons in a conductor is:
A. The speed of light in the conductor
B. The speed of the electric signal along the wire
C. The instantaneous thermal velocity of the electrons
D. The average velocity acquired by electrons in the direction opposite to the applied field ✓ Correct
Solution: Random thermal motion averages to zero; the field superimposes a very small net drift, typically a fraction of a millimetre per second.
Q5 — Electric Current & Ohm's Law · medium · theory
The relation between current $I$ and drift velocity $v_d$ in a conductor of area $A$ with $n$ free electrons per unit volume is:
A. $I = \dfrac{nev_d}{A}$
B. $I = nAe^2v_d$
C. $I = \dfrac{nAe}{v_d}$
D. $I = nAev_d$ ✓ Correct
Solution: In one second the electrons in a cylinder of length $v_d$ cross the section, carrying a total charge $nAev_d$.
Q6 — Electric Current & Ohm's Law · easy · theory
A conductor that does NOT obey Ohm's law is described as:
A. Superconducting
B. A perfect insulator
C. Ohmic
D. Non-ohmic, for example a semiconductor diode ✓ Correct
Solution: For a non-ohmic device the $V$-$I$ graph is not a straight line through the origin, so the resistance depends on the operating point.
Q7 — Electric Current & Ohm's Law · medium · theory
Current density in a conductor is defined as:
A. The potential difference per unit length
B. The current per unit length
C. The current per unit area of cross-section ✓ Correct
D. The charge per unit volume
Solution: $J = \dfrac{I}{A}$, measured in $\text{A/m}^2$. Unlike current, current density is a vector.
Q8 — Electric Current & Ohm's Law · medium · theory
The mobility of a charge carrier is defined as:
A. The drift velocity acquired per unit electric field ✓ Correct
B. The current per unit area
C. The charge carried per unit time
D. The resistance per unit length
Solution: $\mu = \dfrac{v_d}{E}$, measured in $\text{m}^2\text{V}^{-1}\text{s}^{-1}$.
Q9 — Electric Current & Ohm's Law · easy · numerical
A charge of $60\text{ C}$ flows through a conductor in $30\text{ s}$. The current is:
A. $1800\text{ A}$
B. $2\text{ A}$ ✓ Correct
C. $30\text{ A}$
D. $0.5\text{ A}$
Solution: $I = \dfrac{q}{t} = \dfrac{60}{30} = 2\text{ A}$.
Q10 — Electric Current & Ohm's Law · easy · numerical
A current of $2\text{ A}$ flows through a resistance of $5\,\Omega$. The potential difference across it is:
A. $0.4\text{ V}$
B. $2.5\text{ V}$
C. $20\text{ V}$
D. $10\text{ V}$ ✓ Correct
Solution: $V = IR = 2 \times 5 = 10\text{ V}$.
Q11 — Electric Current & Ohm's Law · easy · numerical
A potential difference of $12\text{ V}$ drives a current of $3\text{ A}$ through a conductor. Its resistance is:
A. $36\,\Omega$
B. $9\,\Omega$
C. $0.25\,\Omega$
D. $4\,\Omega$ ✓ Correct
Solution: $R = \dfrac{V}{I} = \dfrac{12}{3} = 4\,\Omega$.
Q12 — Electric Current & Ohm's Law · medium · numerical
A steady current of $2\text{ A}$ flows for $5\text{ minutes}$. The charge transported is:
A. $150\text{ C}$
B. $600\text{ C}$ ✓ Correct
C. $10\text{ C}$
D. $60\text{ C}$
Solution: $q = It = 2 \times 300 = 600\text{ C}$.
Q13 — Electric Current & Ohm's Law · medium · numerical
The number of electrons constituting a charge of $1\text{ C}$ is approximately:
A. $1.6 \times 10^{19}$
B. $6.25 \times 10^{18}$ ✓ Correct
C. $1.6 \times 10^{-19}$
D. $6.02 \times 10^{23}$
Solution: $N = \dfrac{q}{e} = \dfrac{1}{1.6 \times 10^{-19}} \approx 6.25 \times 10^{18}$.
Q14 — Electric Current & Ohm's Law · medium · numerical
A current of $1.6\text{ A}$ flows through a wire. The number of electrons crossing a section per second is:
A. $10^{18}$
B. $10^{19}$ ✓ Correct
C. $1.6 \times 10^{19}$
D. $6.25 \times 10^{18}$
Solution: $N = \dfrac{I}{e} = \dfrac{1.6}{1.6 \times 10^{-19}} = 10^{19}$ electrons per second.
Q15 — Electric Current & Ohm's Law · hard · numerical
A wire of area $10^{-6}\text{ m}^2$ with $8.5 \times 10^{28}$ free electrons per cubic metre carries $1.7\text{ A}$. The drift velocity is approximately:
A. $1.25 \times 10^{-2}\text{ m/s}$
B. $1.25 \times 10^{-4}\text{ m/s}$ ✓ Correct
C. $3 \times 10^8\text{ m/s}$
D. $1.25\text{ m/s}$
Solution: $v_d = \dfrac{I}{nAe} = \dfrac{1.7}{8.5 \times 10^{28} \times 10^{-6} \times 1.6 \times 10^{-19}} \approx 1.25 \times 10^{-4}\text{ m/s}$.
Q16 — Electric Current & Ohm's Law · medium · numerical
A current of $10\text{ A}$ flows through a wire of cross-sectional area $2 \times 10^{-6}\text{ m}^2$. The current density is:
A. $20\text{ A/m}^2$
B. $5 \times 10^6\text{ A/m}^2$ ✓ Correct
C. $2 \times 10^{-7}\text{ A/m}^2$
D. $5 \times 10^5\text{ A/m}^2$
Solution: $J = \dfrac{I}{A} = \dfrac{10}{2 \times 10^{-6}} = 5 \times 10^6\text{ A/m}^2$.
Q17 — Electric Current & Ohm's Law · easy · numerical
A current of $0.5\text{ A}$ flows through a $20\,\Omega$ resistor. The potential difference across it is:
A. $0.025\text{ V}$
B. $20\text{ V}$
C. $10\text{ V}$ ✓ Correct
D. $40\text{ V}$
Solution: $V = IR = 0.5 \times 20 = 10\text{ V}$.
Q18 — Electric Current & Ohm's Law · easy · numerical
An appliance draws $5\text{ A}$ from a $220\text{ V}$ supply. The power consumed is:
A. $44\text{ W}$
B. $5500\text{ W}$
C. $1100\text{ W}$ ✓ Correct
D. $225\text{ W}$
Solution: $P = VI = 220 \times 5 = 1100\text{ W}$.
Q19 — Electric Current & Ohm's Law · medium · numerical
A current of $3\text{ A}$ flows through a $10\,\Omega$ resistor. The power dissipated is:
A. $90\text{ W}$ ✓ Correct
B. $300\text{ W}$
C. $3.3\text{ W}$
D. $30\text{ W}$
Solution: $P = I^2R = 9 \times 10 = 90\text{ W}$.
Q20 — Electric Current & Ohm's Law · medium · numerical
A potential difference of $200\text{ V}$ is applied across a $100\,\Omega$ resistor. The power dissipated is:
A. $200\text{ W}$
B. $400\text{ W}$ ✓ Correct
C. $2\text{ W}$
D. $20000\text{ W}$
Solution: $P = \dfrac{V^2}{R} = \dfrac{40000}{100} = 400\text{ W}$.
Q21 — Electric Current & Ohm's Law · medium · numerical
A $100\text{ W}$ lamp burns for one hour. The electrical energy consumed is:
A. $6000\text{ J}$
B. $3.6 \times 10^5\text{ J}$ ✓ Correct
C. $100\text{ J}$
D. $3600\text{ J}$
Solution: $W = Pt = 100 \times 3600 = 3.6 \times 10^5\text{ J}$, which is $0.1\text{ kWh}$.