Resistivity and its Temperature Dependence

Resistivity and its Temperature Dependence MDCAT MCQs with answers

35 past paper MCQs on Resistivity and its Temperature Dependence, 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.

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1.The unit of resistivity is the: (MDCAT 2020)

  1. ohm
  2. ohm metre
  3. ohm per metre
  4. metre per ohm
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Correct answer: (b) ohm metre

From $\rho=RA/L$ the unit is the ohm metre.

2.The resistance of a conductor does not depend on which of the following? (MDCAT 2022)

  1. area of cross-section
  2. resistivity
  3. length
  4. mass
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Correct answer: (d) mass

$R=\rho L/A$ has no mass in it.

3.What do substances whose resistance decreases with a rise in temperature have? (MDCAT 2022)

  1. a high temperature coefficient
  2. a negative temperature coefficient
  3. a positive temperature coefficient
  4. a zero temperature coefficient
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Correct answer: (b) a negative temperature coefficient

A falling resistance means the temperature coefficient of resistance is negative, as it is for semiconductors.

4.A wire of uniform cross-sectional area $A$, length $L$ and resistance $R$ is cut into two equal parts. What will happen to the resistivity of each part? (MDCAT 2023)

  1. it will be doubled
  2. it will be one fourth
  3. it will be halved
  4. it will remain the same
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Correct answer: (d) it will remain the same

Resistivity depends on the material and its temperature, not on the size of the piece.

5.When the length of a copper wire is doubled, its resistivity becomes: (MDCAT 2024)

  1. double
  2. half
  3. the same
  4. four times
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Correct answer: (c) the same

Resistivity is a property of the material and not of the length; it is the resistance that doubles.

6.The resistance of a semiconductor with a rise in temperature: (MDCAT 2024)

  1. increases
  2. decreases
  3. remains the same
  4. becomes infinite
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Correct answer: (b) decreases

Heating a semiconductor frees many more charge carriers, so its resistance falls.

7.The reciprocal of the resistivity of a material is called its: (UHS MDCAT 2025)

  1. impedance
  2. conductivity
  3. admittance
  4. reactance
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Correct answer: (b) conductivity

Conductivity is the reciprocal of resistivity.

8.If the length of the conductor is made 4 times its original length, its resistance becomes (UHS MDCAT 2025)

  1. quarter
  2. half
  3. zero
  4. 4 times
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Correct answer: (d) 4 times

Resistance is proportional to length, so four times the length is four times the resistance.

9.The unit of temperature coefficient of resistivity is (UHS MDCAT 2025)

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

It is a fractional change in resistivity per degree, so its unit is the reciprocal kelvin.

10.Conductance is reciprocal of resistance, its unit is: (NUMS MDCAT 2025)

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

Conductance is the reciprocal of resistance and is measured in siemens.

11.The fraction change in resistance per kelvin is: (NUMS MDCAT 2025)

  1. Coefficient of conductivity
  2. Temperature coefficient of resistance
  3. Coefficient of conductance
  4. Coefficient of resistivity
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Correct answer: (b) Temperature coefficient of resistance

That fraction is the temperature coefficient of resistance.

12.The value of temperature co-efficient of a conductor is zero. This indicates that with the rise in temperature, resistance of conductor: (SIBA MDCAT 2025)

  1. Increases
  2. Decreases
  3. Remain same
  4. Becomes zero
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Correct answer: (c) Remain same

A zero coefficient means the resistance does not change with temperature at all.

13.154.When length of copper wire is doubled then resistivity becomes: (UHS MDCAT 2024)

  1. Double
  2. Half
  3. Remains same
  4. Four times
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Correct answer: (c) Remains same

Resistivity is a property of the material, so stretching the wire does not change it.

14.155.The resistance of semi-conductor with rise in temperature (UHS MDCAT 2024)

  1. Increases
  2. Decreases
  3. Remain same
  4. Infinite
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Correct answer: (b) Decreases

Heating a semiconductor frees more carriers, so its resistance falls.

15.Temperature coefficient of resistance is defined as increase in resistance per ohm original resistance per ___? (KMU MDCAT 2024)

  1. Degree rise in temperature
  2. Unit increase in electric current
  3. Unit decrease in capacitance
  4. Degree drop in temperature
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Correct answer: (a) Degree rise in temperature

It is the fractional rise in resistance for each degree of temperature.

16.For metals, the temperature coefficient of resistance is: (KMU MDCAT 2024)

  1. Infinity
  2. Negative
  3. Positive
  4. Zero
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Correct answer: (c) Positive

A metal grows more resistive as it is heated, so its coefficient is positive.

17.The substance having negative temperature coefficient of resistance is: (NUMS MDCAT 2024)

  1. Insulators
  2. Conductor
  3. Semi-conductor
  4. Alloys
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Correct answer: (c) Semi-conductor

Heating a semiconductor frees carriers, so its resistance falls and its coefficient is negative.

18.What do the substances whose resistance decreases with increase in temperature have? (UHS MDCAT 2023)

  1. high temperature coefficient
  2. negative temperature coefficient
  3. positive temperature coefficient
  4. zero temperature coefficient
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Correct answer: (b) negative temperature coefficient

A substance whose resistance falls as it warms has a negative temperature coefficient.

19.Ohm meter us the unit of: (SZABMU MDCAT 2023)

  1. Resistance
  2. Resistivity
  3. Conductance
  4. conductivity
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Correct answer: (b) Resistivity

$\rho=RA/L$ has the unit ohm metre.

20.The total resistance of wire isinversely proportional to: (SZABMU MDCAT 2023)

  1. Length
  2. Area
  3. Temperature
  4. Time
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Correct answer: (b) Area

$R=\rho L/A$, so the thicker the wire the smaller its resistance.

21.If length of the wire becomes two times to its original value and area becomes one half to its original value, then resistance of the wire becomes: (NUMS MDCAT 2023)

  1. Double
  2. Four times
  3. One half
  4. One forth
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Correct answer: (b) Four times

$R=\rho L/A$ doubles with the length and doubles again as the area is halved.

22.Which of the following the fractional change in resistance per kelvin? (UHS MDCAT 2023)

  1. Conductivity
  2. Resistivity
  3. Temperature coefficient of resistivity
  4. Temperature coefficient of resistance
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Correct answer: (d) Temperature coefficient of resistance

That fraction is the temperature coefficient of resistance.

23.The following formula can be used to determine the resistance of a length of conductor. R pl/A In the formula, the symbol p stands for the: (UHS MDCAT 2023)

  1. Cross-sectional area of the conductor in m2
  2. Product of the length of the conductor in meters
  3. Resistivity of the material in units of ohm meters
  4. Resistance of the conductor in units of ohms per meter
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Correct answer: (c) Resistivity of the material in units of ohm meters

In $R=\rho L/A$ the symbol $\rho$ is the resistivity, measured in ohm metres.

24.The resistance of the wire varies inversely as: (UHS MDCAT 2023)

  1. Area of cross section
  2. length
  3. Resistivity
  4. Temperature
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Correct answer: (a) Area of cross section

$R=\rho L/A$, so the wider the wire the smaller its resistance.

25.A wire of uniform area of cross-section A’, length ‘L’, and resistance R is cut into two equal parts. What will happen to the resistivity of each part? (UHS MDCAT 2023)

  1. It will be doubled
  2. It will be one fourth
  3. It will be halved
  4. It will remain the same
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Correct answer: (d) It will remain the same

Resistivity is a property of the material, so cutting the wire does not change it.

26.The resistance of a conductor at absolute zero ( OK) is: (PMC MDCAT 2022)

  1. Almost zero
  2. Almost infinite
  3. No prediction at all
  4. May increase or decrease
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Correct answer: (a) Almost zero

With the lattice almost still there is nothing to scatter the electrons, so the resistance falls away.

27.Resistance of a conductor depends upon: (PMC MDCAT 2022)

  1. Temperature
  2. Nature of a conductor
  3. Length
  4. Color
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Correct answer: (c) Length

$R=\rho L/A$: the longer the conductor the greater its resistance.

28.Resistivity of a substance Is defined as the resistance of a _____ of that substance. (PMC MDCAT 2022)

  1. meter
  2. meter square
  3. meter cube
  4. centimeter
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Correct answer: (b) meter square

Resistivity is the resistance of a cube of the material of unit side, measured between opposite faces.

29.The specific resistance of a conductor Increases with: (PMC MDCAT 2022)

  1. Increase in temperature
  2. increase in cross-sectional area
  3. Decrease in length
  4. decrease In cross-sectional area
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Correct answer: (a) Increase in temperature

Heating makes the lattice vibrate more and scatter the electrons, so the resistivity rises.

30.Q.66 The resistance of pure metal increases with: (NUMS MDCAT 2022)

  1. Increase in temperature
  2. Increase in pressure
  3. Decrease in temperature
  4. Decrease in pressure
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Correct answer: (a) Increase in temperature

A metal grows more resistive as it is heated.

31.When a wire is compressed and it’s radius becomes 2R then it’s resistance will be: (PMC MDCAT 2020)

  1. 16R
  2. 4 R
  3. 1 / 16 R
  4. 1 / 4 R
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Correct answer: (c) 1 / 16 R

The volume is fixed, so four times the area means a quarter of the length, and $R$ falls to a sixteenth.

32.The change in resistance of metallic conductor at temperature below 0 degrees is: (PMC MDCAT 2020)

  1. Non-linear
  2. Curve
  3. Linear
  4. Curvilinear
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Correct answer: (c) Linear

Away from very low temperatures the resistance of a metal rises in a straight line with temperature.

33.A copper wire has length L and cross-sectional area A. Its resistance is R. If we halved the length and halved the diameter of wire, then what will be the resistance of this wire? (UHS MDCAT 2019)

  1. 4R
  2. 3R
  3. 2R
  4. R
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Correct answer: (c) 2R

Halving the diameter quarters the area, so $R=\rho(L/2)/(A/4)$ is $2R$.

34.When a potential difference is applied across the ends of a uniform wire of length l and radius r, a current I flows in the wire. If same potential difference is applied to the ends of another wire of the same material but of length 2l and radius 2r, the current in the wire is: (UHS MDCAT 2018)

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

Twice the length doubles the resistance and twice the radius quarters it, so $R$ halves and the current doubles.

35.Resistance between two opposite faces of square thin film of area 1 mm2 having thickness of 1 μm if resistivity of material is 10-6 Ω will be: (UHS MDCAT 2016)

  1. 1000 Ω
  2. 100 Ω
  3. 1 Ω
  4. 10 Ω
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Correct answer: (c) 1 Ω

$R=\rho L/A=10^{-6}\times10^{-3}/(10^{-3}\times10^{-6})$, that is $1\,\Omega$.

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