An electrical cable having a resistance of $0.2\,\,{\rm{\Omega }}$ delivers $10\,\,{\rm{k}}\,{\rm{W}}$ at $200\,\,V\,{\rm{D}}\,{\rm{C}}$ to a factory. What is the efficiency of transmission

$\begin{array}{*{20}{l}} {{\rm{95}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{65}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{75}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{85}}\,\,{\rm{\% }}} \end{array}$

An immersion heater is rated ${\rm{418}}\,\,{\rm{W}}$. It should heat a litre of water from $10\,^\circ C$ to $30\,^\circ C$ in nearly

$\begin{array}{*{20}{l}} {{\rm{200}}\,\,{\rm{s}}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{44}}\,\,{\rm{s}}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{100}}\,\,{\rm{s}}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{400}}\,\,{\rm{s}}} \end{array}$

A wire is stretched so as to change its diameter by ${\rm{0}}{\rm{.25}}\,\,{\rm{\% }}$. The percentage change in resistance is

$\begin{array}{*{20}{l}} {{\rm{1}}{\rm{.0}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{4}}{\rm{.0}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{2}}{\rm{.0}}\,\,{\rm{\% }}} \end{array}$

$\begin{array}{*{20}{l}} {{\rm{0}}{\rm{.5}}\,\,{\rm{\% }}} \end{array}$

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JEE • PHYSICS • CURRENT ELECTRICITY

Current electricity practice · Medium

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Practice format and chapter quiz

These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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Showing 31-60 of 457 questions

31 Medium

31 of 457

Application +4 | -1

If a copper wire is stretched to make it

0.1 \%

longer, the percentage change in its resistance is

View answer and explanation

Correct option: A

0.2 \%

increase

Option A (0.2 % increase) is correct because the percentage change in resistance is twice the percentage change in length.

32 Medium

32 of 457

Remembering +4 | -1

The production of

e.m.f.

by maintaining a difference of temperature between the two junctions of two different metals is known as

View answer and explanation

Correct option: B

Seebeck effect

Option B (Seebeck effect) is correct because the Seebeck effect describes the generation of an electromotive force (emf) due to a temperature difference between two junctions of different metals.

33 Medium

33 of 457

Application +4 | -1

An electrical cable having a resistance of

0.2\,\,\mathrm{\Omega }

delivers

10\,\,\mathrm{k}\,\mathrm{W}

200\,\,V\,\mathrm{D}\,\mathrm{C}

to a factory. What is the efficiency of transmission

View answer and explanation

Correct option: D

\begin{array}{llllllllllllllllllll} {\mathrm{95}\,\,\mathrm{\% }} \end{array}

Option D (

\begin{array}{llllllllllllllllllll}{\mathrm{95}\,\,\mathrm{\% }}\end{array}

) is correct because it represents the efficiency of transmission calculated by accounting for power loss in the cable.

34 Medium

34 of 457

Application +4 | -1

A certain piece of copper is to be shaped into a conductor of minimum resistance. Its length and diameter should be respectively

View answer and explanation

Correct option: C

\ell / 2,2 {d}

The correct answer is C (

\ell / 2, 2{d}

) because this combination minimizes resistance for a given volume of copper.

35 Medium

35 of 457

Analyzing +4 | -1

Twelve wires of equal resistance

R

are connected to form a cube. The effective resistance between two opposite diagonal ends will be

View answer and explanation

Correct option: A

\left( {5/6} \right)R

Option A is correct because the effective resistance between two opposite diagonal ends of a cube formed by twelve wires of equal resistance R is (5/6)R.

36 Medium

36 of 457

Understanding +4 | -1

If current is passed through

\mathrm{Sb}-\mathrm{Bi}

thermocouple then

View answer and explanation

Correct option: A

heat is produced at junction where current is from

{Sb}

{Bi}

Option A (heat is produced at junction where current is from

{Sb}

{Bi}

) is correct because this describes the Peltier effect, where heat is either absorbed or released at the junction of two dissimilar metals depending on the direction of the current.

37 Medium

37 of 457

Application +4 | -1

An immersion heater is rated

\mathrm{418}\,\,\mathrm{W}

. It should heat a litre of water from

10\,^\circ C

30\,^\circ C

in nearly

View answer and explanation

Correct option: C

\begin{array}{llllllllllllllllllll} {\mathrm{200}\,\,\mathrm{s}} \end{array}

Option C (200 s) is correct because it correctly calculates the time required to heat the water using the power of the immersion heater and the specific heat capacity of water.

38 Medium

38 of 457

Analyzing +4 | -1

It is possible that any some constant value of emf, but the potential difference between the plates is zero?

View answer and explanation

Correct option: C

Yes, if another identical battery is joined in opposition

The correct answer is 'Yes, if another identical battery is joined in opposition' because the net emf becomes zero, resulting in zero potential difference despite each battery having a constant emf.

39 Medium

39 of 457

Application +4 | -1

A wire is stretched so as to change its diameter by

\mathrm{0}\mathrm{.25}\,\,\mathrm{\% }

. The percentage change in resistance is

View answer and explanation

Correct option: C

\begin{array}{llllllllllllllllllll} {\mathrm{1}\mathrm{.0}\,\,\mathrm{\% }} \end{array}

Option C (1.0 %) is correct because the percentage change in resistance is calculated based on the change in diameter, considering constant volume.

40 Medium

40 of 457

Understanding +4 | -1

Potentiometer measures the potential difference more accurately than a voltmeter because

View answer and explanation

Correct option: C

It does not draw current from external circuit

Option C (It does not draw current from external circuit) is correct because a potentiometer works on the null deflection method, drawing no current from the circuit being measured, thus providing a more accurate reading.

41 Medium

41 of 457

Understanding +4 | -1

Which one of the following physical quantities does NOT affect the resistance of a cylindrical resistor?

View answer and explanation

Correct option: A

The current through it

Option A (The current through it) is correct because resistance depends on resistivity, length, and area, but not on the current.

42 Medium

42 of 457

Application +4 | -1

Two bulbs when connected in parallel to a source take

\mathrm{100 W}

each. The total power consumed when they are connected in series with the same source is
 

View answer and explanation

Correct option: B

\mathrm{50 W}

Option B (50 W) is correct because the total power consumed in series is half of the individual power when connected in parallel.

43 Medium

43 of 457

Remembering +4 | -1

The current density (number of free electrons per

{\mathrm{m}^3}

) in metallic conductor is of the order of

View answer and explanation

Correct option: D

{10^{28}}

Option D (

{10^{28}}

) is correct because the number density of free electrons in a typical metallic conductor is on the order of

10^{28}

per cubic meter.

44 Medium

44 of 457

Remembering +4 | -1

Potential gradient is defined as

View answer and explanation

Correct option: A

Fall of potential per unit length of the wire

Option A (Fall of potential per unit length of the wire) is correct because potential gradient is defined as the rate of change of potential with respect to distance.

45 Medium

45 of 457

Understanding +4 | -1

Which of the following is the unit of mobility of a electron in a conductor?

View answer and explanation

Correct option: B

{kg}^{-1} {~s}^2 {~A}

Option B (

{kg}^{-1} {~s}^2 {~A}

) is correct because it represents the correct units for mobility, derived from the formula mobility = drift velocity / electric field.

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46 Medium

46 of 457

Remembering +4 | -1

Kirchoff’s second law for the analysis of circuit is based on

View answer and explanation

Correct option: B

Conversion of energy

Option B (Conversion of energy) is correct because Kirchhoff's second law, also known as the loop rule, is based on the principle of conservation of energy.

47 Medium

47 of 457

Understanding +4 | -1

Given a current carrying wire of non-uniform cross section. Which of the following quantity or quantities are constant throughout the length of the wire?

View answer and explanation

Correct option: D

Current only

Option D is correct because in a non-uniform cross-section wire, the current remains constant throughout the length, while the electric field and drift speed vary.

48 Medium

48 of 457

Understanding +4 | -1

Which one of the following statements concerning Ohm's law is true?

View answer and explanation

Correct option: D

Ohm's law is true when the resistivity of a material is independent of the applied electric field

Option D is correct because Ohm's law holds only when the resistivity of the material remains constant, irrespective of the applied electric field.

49 Medium

49 of 457

Understanding +4 | -1

A metallic resistor is connected across a battery. If the number of collisions of the free electrons with the lattice is some how decreased in the resistor (for example by cooling it), the current will

View answer and explanation

Correct option: B

Increase

Option B (Increase) is correct because decreasing collisions increases the relaxation time, leading to a higher drift velocity and thus increased current.

50 Medium

50 of 457

Application +4 | -1

When the current

i

is flowing a conductor, the drift velocity is

v

. If

2i

current is flowed through the same metal but having double the area of cross-section, then the drift velocity will be

View answer and explanation

Correct option: C

v

Option C (

v

) is correct because the drift velocity is proportional to the current density, and the current density remains the same when both current and area are doubled.

51 Medium

51 of 457

Understanding +4 | -1

Statement-1: The value of temperature coefficient of resistance is positive for metals.
Statement-2: The temperature coefficient of resistance for insulator is also positive.

View answer and explanation

Correct option: C

Statement-1 is true, Statement-2 is false

Option C (Statement-1 is true, Statement-2 is false) is correct because metals have a positive temperature coefficient of resistance, while insulators have a negative one.

52 Medium

52 of 457

Application +4 | -1

A generator of emf 100 V has an internal resistance of 0.04 ohm. If its terminal voltage is 95 V, then the current in the circuit is

View answer and explanation

Correct option: C

125 A

Option C (125 A) is correct because it is calculated using Ohm's law with the difference between the emf and terminal voltage.

53 Medium

53 of 457

Understanding +4 | -1

If temperature is decreased, then relaxation time of electrons in metals will

View answer and explanation

Correct option: A

Increase

Option A (Increase) is correct because as temperature decreases, the vibration of atoms in the metal lattice decreases, leading to fewer collisions and a longer relaxation time.

54 Medium

54 of 457

Application +4 | -1

The resistance of hot tungsten filament is about

\mathrm{10}\,\,\mathrm{times}

the cold resistance. What will be the resistance of

\mathrm{100}\,\,\mathrm{W}

and

\mathrm{200}\,\,\mathrm{V}

lamp, when not in use?

View answer and explanation

Correct option: A

\mathrm{40}\,\,\mathrm{\Omega }

Option A (

\mathrm{40}\,\,\mathrm{\Omega }

) is correct because the resistance of the lamp when not in use is the cold resistance, which is 1/10th of the hot resistance.

55 Medium

55 of 457

Understanding +4 | -1

Assertion: Resistivity of metals decreases with decrease in temperature but have some finite value as the temperature approaches absolute zero.
Reason: The residual resistivity near absolute zero is caused primarily by the collision of electrons with impurities and imperfections in the metal.

View answer and explanation

Correct option: A

If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion

Option A is correct because both the Assertion and Reason are true, and the Reason correctly explains why metals have a finite resistivity at absolute zero due to impurities and imperfections.

56 Medium

56 of 457

Application +4 | -1

A wire of resistance

4 \Omega

is used to wind a coil of radius

7 \mathrm{~cm}

. The wire has a diameter of

1.4 \mathrm{~mm}

and the specific resistance of its material is

2 \times 10^{-7} \Omega m

. Find the number of turns in the coil.

View answer and explanation

Correct option: A

n =70

Option A (

n =70

) is correct because it is the number of turns calculated using the resistance, specific resistance, and dimensions of the wire.

57 Medium

57 of 457

Understanding +4 | -1

Assertion: There is no current in the metals in the absence of electric field.

Reason: Motion of free electrons are randomly.

View answer and explanation

Correct option: A

If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Option A (If both Assertion and Reason are true and Reason is the correct explanation of Assertion) is correct because the random motion of free electrons cancels out, resulting in no net current without an electric field.

58 Medium

58 of 457

Analyzing +4 | -1

Assertion: Terminal potential difference of a cell is always less than its emf.
Reason: Potential drop due to internal resistance of cell increases the terminal potential difference.

View answer and explanation

Correct option: D

If both Assertion & Reason are False

Option D (If both Assertion & Reason are False) is correct because the terminal potential difference can be greater than the emf during charging, and the potential drop due to internal resistance decreases the terminal potential difference.

59 Medium

59 of 457

Understanding +4 | -1

A metallic block has no potential difference applied across it, then the mean velocity of free electrons at absolute temperature

T

View answer and explanation

Correct option: C

Zero

Option C (Zero) is correct because in the absence of an applied electric field, the free electrons move randomly, resulting in a zero mean velocity.

60 Medium

60 of 457

Understanding +4 | -1

Consider the following two statements:

I. Kirchhoff's junction law follows from the conservation of charge.

II. Kirchhoff's loop law follows from the conservation of energy.

Which of the following is correct?

View answer and explanation

Correct option: D

Both I and II are correct

Option D is correct. Kirchhoff's junction law is based on the conservation of charge, and Kirchhoff's loop law is based on the conservation of energy.

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