Page 1
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1. A quantity Q is formulated as . X, Y, and Z are independent
parameters which have fractional errors of 0.1, 0.2, and 0.5, respectively in measurement.
The maximum fractional error of Q is [2025]
(a) 0.6
(b) 0.8
(c) 0.7
(d) 0.1
Ans: (c)
The quantity Q is expressed as . The variables X, Y, and Z are
independent parameters with fractional errors of 0.1, 0.2, and 0.5, respectively. To determine the
maximum fractional error in Q, we can use the following method:
Fractional error in
Substituting the fractional errors into the equation:
Calculating each term gives:
= 0.2 + 0.3 + 0.2
Summing these values results in:
= 0.7
Thus, the maximum fractional error in Q is 0.7.
Q2: The dimension of is equal to that of: (µ
0
= Vacuum permeability and ?
0
=
Vacuum permittivity) [2025]
(a) Voltage
(b) Inductance
(c) Resistance
(d) Capacitance
Ans: (c)
Page 2
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1. A quantity Q is formulated as . X, Y, and Z are independent
parameters which have fractional errors of 0.1, 0.2, and 0.5, respectively in measurement.
The maximum fractional error of Q is [2025]
(a) 0.6
(b) 0.8
(c) 0.7
(d) 0.1
Ans: (c)
The quantity Q is expressed as . The variables X, Y, and Z are
independent parameters with fractional errors of 0.1, 0.2, and 0.5, respectively. To determine the
maximum fractional error in Q, we can use the following method:
Fractional error in
Substituting the fractional errors into the equation:
Calculating each term gives:
= 0.2 + 0.3 + 0.2
Summing these values results in:
= 0.7
Thus, the maximum fractional error in Q is 0.7.
Q2: The dimension of is equal to that of: (µ
0
= Vacuum permeability and ?
0
=
Vacuum permittivity) [2025]
(a) Voltage
(b) Inductance
(c) Resistance
(d) Capacitance
Ans: (c)
The dimension of can be understood as follows:
Vacuum permeability (µ
0
) and vacuum permittivity (?
0
) relate to the properties of inductance and
capacitance, respectively, in a vacuum. We start by considering the formulas for inductance (L)
and capacitance (C):
Inductance (L) is given by:
Capacitance (C) is given by:
From these, the ratio L/C can be expressed as :
Taking the square root of this ratio, we have:
This simplifies further to considering the relationship between time constant (t) and resistance
(R):
Thus, by taking the square root:
In conclusion, the dimension of is equivalent to the dimension of resistance, R.
Q3: Match List - I with List - II. [2025]
Choose the correct answer from the options given below :
Page 3
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1. A quantity Q is formulated as . X, Y, and Z are independent
parameters which have fractional errors of 0.1, 0.2, and 0.5, respectively in measurement.
The maximum fractional error of Q is [2025]
(a) 0.6
(b) 0.8
(c) 0.7
(d) 0.1
Ans: (c)
The quantity Q is expressed as . The variables X, Y, and Z are
independent parameters with fractional errors of 0.1, 0.2, and 0.5, respectively. To determine the
maximum fractional error in Q, we can use the following method:
Fractional error in
Substituting the fractional errors into the equation:
Calculating each term gives:
= 0.2 + 0.3 + 0.2
Summing these values results in:
= 0.7
Thus, the maximum fractional error in Q is 0.7.
Q2: The dimension of is equal to that of: (µ
0
= Vacuum permeability and ?
0
=
Vacuum permittivity) [2025]
(a) Voltage
(b) Inductance
(c) Resistance
(d) Capacitance
Ans: (c)
The dimension of can be understood as follows:
Vacuum permeability (µ
0
) and vacuum permittivity (?
0
) relate to the properties of inductance and
capacitance, respectively, in a vacuum. We start by considering the formulas for inductance (L)
and capacitance (C):
Inductance (L) is given by:
Capacitance (C) is given by:
From these, the ratio L/C can be expressed as :
Taking the square root of this ratio, we have:
This simplifies further to considering the relationship between time constant (t) and resistance
(R):
Thus, by taking the square root:
In conclusion, the dimension of is equivalent to the dimension of resistance, R.
Q3: Match List - I with List - II. [2025]
Choose the correct answer from the options given below :
(a) (A)-(IV), (B)-(II), (C)-(III), (D)-(I)
(b) (A)-(II), (B)-(III), (C)-(IV), (D)-(I)
(c) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
(d) (A)-(IV), (B)-(II), (C)-(I), (D)-(III)
Ans: (d)
(A) Mass density:
Mass density is defined as mass per unit volume.
The dimension of mass is [M].
The dimension of volume is [L
3
].
Therefore, the dimension of mass density is
Matches with (IV).
(B) Impulse:
Impulse is defined as the change in momentum, or force multiplied by time.
Impulse = Force x Time
The dimension of force is [MLT
-2
].
The dimension of time is [T].
Therefore, the dimension of impulse is [MLT
-2
] ·[T] = [MLT
-1
].
Matches with (II).
(C) Power:
Power is defined as the rate of doing work or energy per unit time.
Power = Work / Time
The dimension of work (or energy) is [ML
2
T
-2
]
The dimension of time is [T].
Therefore, the dimension of power is
Matches with (I).
(D) Moment of inertia:
Moment of inertia is defined as I = m
2
, where m is mass and r is the distance from the axis of
rotation.
The dimension of mass is [M].
The dimension of distance squared is [
2
].
Therefore, the dimension of moment of inertia is [ML
2
T
0
]
Matches with (III).
So, the correct matches are:
(A) - (IV)
(B) - (II)
(C) - (I)
(D) - (III)
Therefore, the correct option is D.
Q4: In an electromagnetic system, a quantity defined as the ratio of electric dipole
moment and magnetic dipole moment has dimension of [M
P
L
Q
T
R
A
S
] . The value of P and
Page 4
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1. A quantity Q is formulated as . X, Y, and Z are independent
parameters which have fractional errors of 0.1, 0.2, and 0.5, respectively in measurement.
The maximum fractional error of Q is [2025]
(a) 0.6
(b) 0.8
(c) 0.7
(d) 0.1
Ans: (c)
The quantity Q is expressed as . The variables X, Y, and Z are
independent parameters with fractional errors of 0.1, 0.2, and 0.5, respectively. To determine the
maximum fractional error in Q, we can use the following method:
Fractional error in
Substituting the fractional errors into the equation:
Calculating each term gives:
= 0.2 + 0.3 + 0.2
Summing these values results in:
= 0.7
Thus, the maximum fractional error in Q is 0.7.
Q2: The dimension of is equal to that of: (µ
0
= Vacuum permeability and ?
0
=
Vacuum permittivity) [2025]
(a) Voltage
(b) Inductance
(c) Resistance
(d) Capacitance
Ans: (c)
The dimension of can be understood as follows:
Vacuum permeability (µ
0
) and vacuum permittivity (?
0
) relate to the properties of inductance and
capacitance, respectively, in a vacuum. We start by considering the formulas for inductance (L)
and capacitance (C):
Inductance (L) is given by:
Capacitance (C) is given by:
From these, the ratio L/C can be expressed as :
Taking the square root of this ratio, we have:
This simplifies further to considering the relationship between time constant (t) and resistance
(R):
Thus, by taking the square root:
In conclusion, the dimension of is equivalent to the dimension of resistance, R.
Q3: Match List - I with List - II. [2025]
Choose the correct answer from the options given below :
(a) (A)-(IV), (B)-(II), (C)-(III), (D)-(I)
(b) (A)-(II), (B)-(III), (C)-(IV), (D)-(I)
(c) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
(d) (A)-(IV), (B)-(II), (C)-(I), (D)-(III)
Ans: (d)
(A) Mass density:
Mass density is defined as mass per unit volume.
The dimension of mass is [M].
The dimension of volume is [L
3
].
Therefore, the dimension of mass density is
Matches with (IV).
(B) Impulse:
Impulse is defined as the change in momentum, or force multiplied by time.
Impulse = Force x Time
The dimension of force is [MLT
-2
].
The dimension of time is [T].
Therefore, the dimension of impulse is [MLT
-2
] ·[T] = [MLT
-1
].
Matches with (II).
(C) Power:
Power is defined as the rate of doing work or energy per unit time.
Power = Work / Time
The dimension of work (or energy) is [ML
2
T
-2
]
The dimension of time is [T].
Therefore, the dimension of power is
Matches with (I).
(D) Moment of inertia:
Moment of inertia is defined as I = m
2
, where m is mass and r is the distance from the axis of
rotation.
The dimension of mass is [M].
The dimension of distance squared is [
2
].
Therefore, the dimension of moment of inertia is [ML
2
T
0
]
Matches with (III).
So, the correct matches are:
(A) - (IV)
(B) - (II)
(C) - (I)
(D) - (III)
Therefore, the correct option is D.
Q4: In an electromagnetic system, a quantity defined as the ratio of electric dipole
moment and magnetic dipole moment has dimension of [M
P
L
Q
T
R
A
S
] . The value of P and
Q are : [2025]
(a) -1, 0
(b) 0, -1
(c) -1, 1
(d) 1, -1
Ans: (b)
After compering values of P & Q are 0 , - 1
Q5: For the determination of refractive index of glass slab, a travelling microscope is
used whose main scale contains 300 equal divisions equals to 15 cm . The vernier scale
attached to the microscope has 25 divisions equals to 24 divisions of main scale. The
least count (LC) of the travelling microscope is (in cm): [2025]
(a) 0.002
(b) 0.0025
(c) 0.0005
(d) 0.001
Ans: (a)
Determine one main scale division (msd):
300 msd = 15 cm
Therefore,
1 msd = 15/300 cm = 0.05 cm
Determine one vernier scale division (vsd):
25 vsd = 24 vsd
Therefore,
1 vsd = 24/25 msd
Calculate the least count (LC):
The least count is given by the difference between one main scale division and one vernier
scale division:
LC = 1 msd - 1 vsd
Substitute the expression for 1 vsd:
This simplifies to:
Page 5
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1. A quantity Q is formulated as . X, Y, and Z are independent
parameters which have fractional errors of 0.1, 0.2, and 0.5, respectively in measurement.
The maximum fractional error of Q is [2025]
(a) 0.6
(b) 0.8
(c) 0.7
(d) 0.1
Ans: (c)
The quantity Q is expressed as . The variables X, Y, and Z are
independent parameters with fractional errors of 0.1, 0.2, and 0.5, respectively. To determine the
maximum fractional error in Q, we can use the following method:
Fractional error in
Substituting the fractional errors into the equation:
Calculating each term gives:
= 0.2 + 0.3 + 0.2
Summing these values results in:
= 0.7
Thus, the maximum fractional error in Q is 0.7.
Q2: The dimension of is equal to that of: (µ
0
= Vacuum permeability and ?
0
=
Vacuum permittivity) [2025]
(a) Voltage
(b) Inductance
(c) Resistance
(d) Capacitance
Ans: (c)
The dimension of can be understood as follows:
Vacuum permeability (µ
0
) and vacuum permittivity (?
0
) relate to the properties of inductance and
capacitance, respectively, in a vacuum. We start by considering the formulas for inductance (L)
and capacitance (C):
Inductance (L) is given by:
Capacitance (C) is given by:
From these, the ratio L/C can be expressed as :
Taking the square root of this ratio, we have:
This simplifies further to considering the relationship between time constant (t) and resistance
(R):
Thus, by taking the square root:
In conclusion, the dimension of is equivalent to the dimension of resistance, R.
Q3: Match List - I with List - II. [2025]
Choose the correct answer from the options given below :
(a) (A)-(IV), (B)-(II), (C)-(III), (D)-(I)
(b) (A)-(II), (B)-(III), (C)-(IV), (D)-(I)
(c) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
(d) (A)-(IV), (B)-(II), (C)-(I), (D)-(III)
Ans: (d)
(A) Mass density:
Mass density is defined as mass per unit volume.
The dimension of mass is [M].
The dimension of volume is [L
3
].
Therefore, the dimension of mass density is
Matches with (IV).
(B) Impulse:
Impulse is defined as the change in momentum, or force multiplied by time.
Impulse = Force x Time
The dimension of force is [MLT
-2
].
The dimension of time is [T].
Therefore, the dimension of impulse is [MLT
-2
] ·[T] = [MLT
-1
].
Matches with (II).
(C) Power:
Power is defined as the rate of doing work or energy per unit time.
Power = Work / Time
The dimension of work (or energy) is [ML
2
T
-2
]
The dimension of time is [T].
Therefore, the dimension of power is
Matches with (I).
(D) Moment of inertia:
Moment of inertia is defined as I = m
2
, where m is mass and r is the distance from the axis of
rotation.
The dimension of mass is [M].
The dimension of distance squared is [
2
].
Therefore, the dimension of moment of inertia is [ML
2
T
0
]
Matches with (III).
So, the correct matches are:
(A) - (IV)
(B) - (II)
(C) - (I)
(D) - (III)
Therefore, the correct option is D.
Q4: In an electromagnetic system, a quantity defined as the ratio of electric dipole
moment and magnetic dipole moment has dimension of [M
P
L
Q
T
R
A
S
] . The value of P and
Q are : [2025]
(a) -1, 0
(b) 0, -1
(c) -1, 1
(d) 1, -1
Ans: (b)
After compering values of P & Q are 0 , - 1
Q5: For the determination of refractive index of glass slab, a travelling microscope is
used whose main scale contains 300 equal divisions equals to 15 cm . The vernier scale
attached to the microscope has 25 divisions equals to 24 divisions of main scale. The
least count (LC) of the travelling microscope is (in cm): [2025]
(a) 0.002
(b) 0.0025
(c) 0.0005
(d) 0.001
Ans: (a)
Determine one main scale division (msd):
300 msd = 15 cm
Therefore,
1 msd = 15/300 cm = 0.05 cm
Determine one vernier scale division (vsd):
25 vsd = 24 vsd
Therefore,
1 vsd = 24/25 msd
Calculate the least count (LC):
The least count is given by the difference between one main scale division and one vernier
scale division:
LC = 1 msd - 1 vsd
Substitute the expression for 1 vsd:
This simplifies to:
Calculate the LC in cm:
Substituting the value of 1 msd:
Hence, the least count of the traveling microscope is 0.002 cm.
Q6: In an electromagnetic system, the quantity representing the ratio of electric flux and
magnetic flux has dimension of M
P
L
Q
T
R
A
S
, where value of 'Q' and 'R' are [2025]
(a) (3, -5)
(b) (-2, 1)
(c) (-2, 2)
(d) (1, -1)
Ans: (d)
To solve this problem, we need to find the dimensions of the electric flux and the magnetic flux,
and then take their ratio.
Determine the dimension of electric flux (F?)
Electric flux is defined as
The electric field E has dimensions:
Since force has dimensions MLT
-2
, and charge (in SI) has dimensions AT, we get:
The area element dA has dimensions L
2
.
Thus, the electric flux has dimensions:
Determine the dimension of magnetic flux (F_B):
Magnetic flux is defined as
The magnetic field B has dimensions determined via the Lorentz force law (using F = q v B),
giving:
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