Ohm’s Law

Ohm’s Law MDCAT MCQs with answers

47 past paper MCQs on Ohm’s Law, from the Current Electricity unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.The statement that the magnitude of the current in a metal is proportional to the potential difference across it as long as the temperature of the conductor is kept constant is known as: (MDCAT 2024)

  1. Joule's law
  2. Gauss's law
  3. Ohm's law
  4. Ampere's law
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Correct answer: (c) Ohm's law

That proportionality at constant temperature is Ohm's law, $V=IR$.

2.A resistor of \$6\,\Omega\$ with a tolerance of 10% and another of \$4\,\Omega\$ with a tolerance of 10% are joined in series. The tolerance of the combination is about: (UHS MDCAT 2017)

  1. 5%
  2. 12%
  3. 10%
  4. 13%
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Correct answer: (c) 10%

The uncertainties add: $0.6+0.4=1.0\,\Omega$ in $10\,\Omega$, which is again 10%.

3.A wire of resistance \$4\,\Omega\$ is bent into a circle. The resistance between the ends of any diameter is: (UHS MDCAT 2017)

  1. $1\,\Omega$
  2. $2\,\Omega$
  3. $4\,\Omega$
  4. $8\,\Omega$
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Correct answer: (a) $1\,\Omega$

A diameter splits the wire into two $2\,\Omega$ halves in parallel, giving $1\,\Omega$.

4.When resistances are joined in series, the equivalent resistance is equal to the: (UHS MDCAT 2017)

  1. product of the reciprocals of the individual resistances
  2. sum of the reciprocals of the individual resistances
  3. product of the individual resistances
  4. sum of the individual resistances
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Correct answer: (d) sum of the individual resistances

The same current passes through each, so the potential drops add and the resistances add with them.

5.If the potential difference (V) across a conductor is doubled, keeping resistance (R) constant, the power dissipated (P) becomes: (KMU MDCAT 2025)

  1. Doubled
  2. Halved
  3. Four times
  4. Remains unchanged
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Correct answer: (c) Four times

$P=V^2/R$, so twice the voltage across the same resistance dissipates four times the power.

6.If voltage across a resistor is doubled then its resistance will become: (temperature and physical state of the conductor remains constant). (SZABMU MDCAT 2025)

  1. Doubled
  2. Half
  3. Four times
  4. Remains constant
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Correct answer: (d) Remains constant

Resistance is a property of the conductor, so it is unchanged; the current doubles instead.

7.High slope of Ohm's law graph means (SZABMU MDCAT 2025)

  1. Low resistance
  2. High resistance
  3. Open circuit
  4. Low current
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Correct answer: (a) Low resistance

On a graph of current against potential difference the slope is $1/R$, so a steep line means a small resistance.

8.What will potential difference, if a wire has resistance of 10Ω and current 2A flow through it : (SZABMU MDCAT 2025)

  1. 5V
  2. 10V
  3. 20V
  4. 40V
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Correct answer: (c) 20V

$V=IR=2\times10$, which is $20\,\mathrm{V}$.

9.153.The magnitude of the current in metals is proportional to the potential difference across it as long as temperature of conductor is kept constant is known as: (UHS MDCAT 2024)

  1. Joule's Law
  2. Gauss Law
  3. Ohm's Law
  4. Ampere's Law
Show answer

Correct answer: (c) Ohm's Law

That is Ohm’s law.

10.156.Volt x Ampere is the measure of; (UHS MDCAT 2024)

  1. Current
  2. Volt
  3. Resistance
  4. Power
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Correct answer: (d) Power

Volts times amperes is watts, the unit of power.

11.The I-V Graph for a non-Ohmic material is always (KMU MDCAT 2024)

  1. Curved
  2. Horizontal
  3. Linear
  4. Perpendicular
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Correct answer: (a) Curved

A non-ohmic conductor has no constant resistance, so its current voltage graph is not a straight line.

12.If R1 and R2 are respectively the filament resistance of a 100-Watt bulb and 200-Watt bulb designed to operate on the same voltage, then power of: (KMU MDCAT 2024)

  1. R1 is two times R2
  2. R2 is two times R1
  3. R2 is four times R1
  4. R1 is four times R2
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Correct answer: (a) R1 is two times R2

$R=V^2/P$ at the same voltage, so the $100\,\mathrm{W}$ filament has twice the resistance of the $200\,\mathrm{W}$ one.

13.Equivalent resistance between A and B (three 1Ω resistors in parallel): (NUMS MDCAT 2024)

  1. 3/2 Ω
  2. 1/3 Ω
  3. 3 Ω
  4. 2/3 Ω
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Correct answer: (b) 1/3 Ω

Three equal resistors in parallel give a third of one of them.

14.How much potential drop exist across closed switch? (UHS MDCAT 2023)

  1. 0 V
  2. 1V
  3. 2V
  4. 3V
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Correct answer: (a) 0 V

A closed switch is a length of conductor with no resistance, so no potential is dropped across it.

15.A 3 V battery is connected in series with ammeter and 2 ohm resistance after short circuiting circuiting. What will be the reading of ammeter? (UHS MDCAT 2023)

  1. 1 A
  2. 1.5 A
  3. 5 A
  4. 6 A
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Correct answer: (b) 1.5 A

$I=V/R=3/2$, which is $1.5\,\mathrm{A}$.

16.Which of the following statement is NOT CORRECT about Kirchhoff's rule? (UHS MDCAT 2023)

  1. Kirchhoff's current rule based upon the law of conservation of charge
  2. Wheatstone bridge is an application of Kirchhoff's rule
  3. Kirchhoff's rules are more suitable in AC circuits
  4. Kirchhoff's voltage rule based upon the law of conservation of energy
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Correct answer: (c) Kirchhoff's rules are more suitable in AC circuits

The rules were framed for steady currents; alternating circuits need reactance as well as resistance.

17.Volt × Ampere is the unit of: (NUMS MDCAT 2023)

  1. Current
  2. Volt
  3. Resistance
  4. Power
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Correct answer: (d) Power

Volts times amperes is watts, the unit of power.

18.The ohmmeter of a portable digital multi meter need: (UHS MDCAT 2023)

  1. Internal battery
  2. Wet cell
  3. Voltmeter
  4. Ammeter
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Correct answer: (a) Internal battery

An ohmmeter must drive its own current through the resistor, so it carries a battery.

19.Calculate the work done in a resistor of 20 ohm carrying 5A of current in 3 hours? (PMC MDCAT 2022)

  1. 1 kWh
  2. 1.5 kWh
  3. 2 kWh
  4. 3 kWh
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Correct answer: (b) 1.5 kWh

$P=I^2R=25\times20=500\,\mathrm{W}$, and $500\times3$ watt hours is $1.5\,\mathrm{kWh}$.

20.Basically a potentiometer is a device for: (PMC MDCAT 2022)

  1. Comparing two voltage
  2. Measuring current
  3. Comparing two currents
  4. Measuring voltage
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Correct answer: (a) Comparing two voltage

A potentiometer balances one emf against another, so it compares voltages without drawing current.

21.Which of the following statements is true? (PMC MDCAT 2022)

  1. Power is proportional to voltage only
  2. Power is proportional to current only
  3. Power is neither proportional to voltage nor to the current
  4. Power is proportional to both the voltage and current
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Correct answer: (d) Power is proportional to both the voltage and current

$P=VI$, so it rises with either.

22.Ohm’s law is applicable to (PMC MDCAT 2022)

  1. Semiconductors
  2. Vacuum tubes
  3. Carbon resistors
  4. Conductors
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Correct answer: (d) Conductors

Ohm’s law holds for metallic conductors at constant temperature; semiconductors and valve tubes are non-ohmic.

23.In series circuit, current remains? (PMC MDCAT 2022)

  1. Same
  2. Different
  3. Variable
  4. Zero
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Correct answer: (a) Same

There is only one path in a series circuit, so the same current passes through every element.

24.In parallel voltage remains? (PMC MDCAT 2022)

  1. Same
  2. Different
  3. Variable
  4. Zero
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Correct answer: (a) Same

Elements in parallel are connected across the same two points, so they share the same voltage.

25.A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is: (PMC MDCAT 2022)

  1. 6.4 a,6.9 a
  2. 6.4 a, 9.6 a
  3. 4.6 a,6.9 a
  4. 4.6 a,9.6 a
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Correct answer: (b) 6.4 a, 9.6 a

The current divides in inverse ratio to the resistances, giving $9.6\,\mathrm{A}$ in the $8\,\Omega$ branch and $6.4\,\mathrm{A}$ in the other.

26.The circuit which gives continuously varying potential is called: (PMC MDCAT 2022)

  1. Complex network
  2. Wheatstone bridge
  3. Potential divider
  4. Galvanometer
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Correct answer: (c) Potential divider

A potential divider taps off any fraction of the supply voltage as the slider is moved.

27.The sensitivity of a potentiometer can be Increased by ____ (PMC MDCAT 2022)

  1. Increasing the e.m.f of the primary coil
  2. Increasing the Potential gradient
  3. lncreasing the length of the potentiometer wire
  4. Decreasing the length of the potentiometer wire
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Correct answer: (c) lncreasing the length of the potentiometer wire

A longer wire gives a smaller potential gradient, so a given voltage is balanced over a greater length.

28.Which one of the following is a disadvantage of a potentiometer over a voltmeter? (PMC MDCAT 2022)

  1. It can measure internal resistance of a cell
  2. It can measure the e.m.f. of a cell
  3. It is heavy and not portable
  4. It can measure accurately very small pd. of the microvolt
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Correct answer: (c) It is heavy and not portable

The potentiometer is accurate but bulky, and it must be set up and balanced for each reading.

29.The SI Unit for resistance is? (PMC MDCAT 2022)

  1. Ohm
  2. Ampere
  3. Watt
  4. Volts
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Correct answer: (a) Ohm

Resistance is measured in ohms.

30.__________ relationship exists between current and voltage in terms of Ohm’s law: (PMC MDCAT 2022)

  1. Non linear
  2. Varying
  3. Linear
  4. Alternating
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Correct answer: (c) Linear

$V=IR$ with $R$ constant is the equation of a straight line.

31.Ohm’s Law is applicable only when temperature is: (PMC MDCAT 2022)

  1. changing
  2. absolute zero
  3. constant
  4. decreasing
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Correct answer: (c) constant

Resistance changes with temperature, so Ohm’s law holds only while the temperature is held.

32.Ohm’s law is valid when the temperature of conductor Is : (PMC MDCAT 2022)

  1. Very low
  2. Very high
  3. Varying
  4. Constant
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Correct answer: (d) Constant

Resistance changes with temperature, so the law holds only while the temperature is held constant.

33.Correct form of ohm’s law (PMC MDCAT 2022)

  1. I = VR
  2. V = I/R
  3. V = IR
  4. R= IV
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Correct answer: (c) V = IR

Ohm’s law is $V=IR$.

34.In order to achieve high accuraccy, the slide wire of a potentiometer should be (PMC MDCAT 2022)

  1. As long as possible
  2. As short as possible
  3. Neither too small not to large
  4. Very thick
Show answer

Correct answer: (a) As long as possible

A long wire gives a small potential gradient, so the balance point can be read finely.

35.Q.65 A magnitude of the current in metals is proportional to the applied voltage as long as temperature of conductor is kept constant. It is statement of: (NUMS MDCAT 2022)

  1. Joule's law
  2. Gauss's law
  3. Ohm, law
  4. Ampere's law
Show answer

Correct answer: (c) Ohm, law

That is Ohm’s law.

36.Ohm’s Law is not applicable when the temperature is: (PMC Practice 2021)

  1. Changing
  2. Constant
  3. All of These
  4. None of these
Show answer

Correct answer: (a) Changing

Resistance changes with temperature, so the law holds only while the temperature is held.

37.Formula for Power is? (PMC Practice 2021)

  1. P =IV
  2. P=V/I
  3. p=V+I
  4. p=VQ
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Correct answer: (a) P =IV

Electrical power is the product of current and potential difference.

38.In a lamp load, when more than one lamp are switched on, the total resistance of the load: (PMC Practice 2021)

  1. Increases
  2. Decreases
  3. Remains same
  4. None of the above
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Correct answer: (b) Decreases

The lamps are in parallel, so each one added gives the current another path.

39.Electric power is? (PMC Practice 2021)

  1. Rate of electric work done per unit time
  2. Voltage per unit time
  3. Electric charge per unit time
  4. Current per unit time
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Correct answer: (a) Rate of electric work done per unit time

Electrical power is the work done by the current in unit time.

40.An example of a non-ohmic resistor is: (PMC Practice 2021)

  1. Diode
  2. Tungsten wire
  3. Carbon resistor
  4. Copper wire
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Correct answer: (a) Diode

A diode conducts one way and not the other, so its current voltage graph is not a straight line.

41.Galvanometer is an? (PMC Practice 2021)

  1. Electromechanical device
  2. Electrosolar device
  3. Electrothermal device
  4. None of these options is correct
Show answer

Correct answer: (a) Electromechanical device

A galvanometer turns a current into a mechanical deflection, so it is electromechanical.

42.Find the resistance if the voltage of a circuit is 45 volts and current is 30 Amperes? (PMC Practice 2021)

  1. 1.6 Ohms
  2. 1.5 Ohms
  3. 1.7 Ohms
  4. 1.8 Ohms
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Correct answer: (b) 1.5 Ohms

$R=V/I=45/30$, that is $1.5\,\Omega$.

43.One of the following is an Ohmic device: (PMC MDCAT 2020)

  1. Filament bulb
  2. Semiconductor diode
  3. Transistor
  4. Copper wire
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Correct answer: (d) Copper wire

A copper wire at constant temperature obeys Ohm’s law; the other three do not.

44.Calculate the rate at which energy is transferred by 220 V mains supply, which provides a current of 0.1 A to a LED? (UHS MDCAT 2019)

  1. 2.2 W
  2. 2.2 kW
  3. 22 kW
  4. 22 W
Show answer

Correct answer: (d) 22 W

$P=VI=220\times0.1$, that is $22\,\mathrm{W}$.

45.A wire of resistance 4Ω is bent in the form of a circle. The resistance between the ends of any diameter is: (UHS MDCAT 2017)

  1. 1 Ω
  2. 2 Ω
  3. 4 Ω
  4. 8 Ω
Show answer

Correct answer: (a) 1 Ω

The diameter divides the ring into two arcs of $2\,\Omega$ each in parallel, that is $1\,\Omega$.

46.A resistor of 6 Ω with a tolerance of 10% and another of 4 Ω with a tolerance of 10% are connected in series. The tolerance of combination is about: (UHS MDCAT 2017)

  1. 5%
  2. 12%
  3. 10%
  4. 13%
Show answer

Correct answer: (c) 10%

Both resistances carry the same fractional uncertainty, so the sum carries it too.

47.When resistances are connected in series, the equivalent resistances is equal to: (UHS MDCAT 2017)

  1. Product of the reciprocals of the individual resistances
  2. Sum of the reciprocals of the individual resistances
  3. Product of the individual resistances
  4. Sum of the individual resistances
Show answer

Correct answer: (d) Sum of the individual resistances

Resistances in series simply add.

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