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JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Page 2
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Page 3
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Page 4
JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1: Match List - I with List - II.
List I (Number) List II (Significant figure)
(A) 1001 (I) 3
(B) 010.1 (II) 4
(C) 100.100 (III) 5
(D) 0.0010010 (IV) 6
Choose the correct answer from the options given below :
(a) (A)-(II), (B)-(I), (C)-(IV), (D)-(III)
(b) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
(c) (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
(d) (A)-(III), (B)-(IV), (C)-(II), (D)-(I) [JEE Main 2024 (Online) 1st February Evening Shift]
Ans: (a)
Significant figures in a number represent the digits that carry meaning contributing to its precision. This
includes all digits except:
All leading zeros.
Trailing zeros only when they are merely placeholders to indicate the scale of the number (they must
not be significant if there is no decimal point).
Here is the explanation for the significant figures of each number in List I:
(A) 1001 - All the digits in this number are significant because there are no leading or trailing zeros acting
as placeholders. Hence, this number has 4 significant figures.
(B) 010.1 - The leading zero is not significant, but the zero between 1 and the decimal point, the
1itself, andthe1 after the decimal point are all significant. So, this number has 3 significant figures.
(C) 100.100 - Here, the number has zeros which are significant since they are between significant digits
or after the decimal point. This makes all the zeros and the 1s significant. Therefore, the number has 6
significant figures.
(D) 0.0010010 - The leading zeros are not significant, but the three zeros within and at the end of the
number are significant because they are between significant digits or at the end of the number after the
decimal. Therefore, this number has 5 significant figures.
2024
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JEE Main Previous Year Questions
(2021-2025): Units & Measurements
2025
Q1: Match List - I with List - II.
List I (Number) List II (Significant figure)
(A) 1001 (I) 3
(B) 010.1 (II) 4
(C) 100.100 (III) 5
(D) 0.0010010 (IV) 6
Choose the correct answer from the options given below :
(a) (A)-(II), (B)-(I), (C)-(IV), (D)-(III)
(b) (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
(c) (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
(d) (A)-(III), (B)-(IV), (C)-(II), (D)-(I) [JEE Main 2024 (Online) 1st February Evening Shift]
Ans: (a)
Significant figures in a number represent the digits that carry meaning contributing to its precision. This
includes all digits except:
All leading zeros.
Trailing zeros only when they are merely placeholders to indicate the scale of the number (they must
not be significant if there is no decimal point).
Here is the explanation for the significant figures of each number in List I:
(A) 1001 - All the digits in this number are significant because there are no leading or trailing zeros acting
as placeholders. Hence, this number has 4 significant figures.
(B) 010.1 - The leading zero is not significant, but the zero between 1 and the decimal point, the
1itself, andthe1 after the decimal point are all significant. So, this number has 3 significant figures.
(C) 100.100 - Here, the number has zeros which are significant since they are between significant digits
or after the decimal point. This makes all the zeros and the 1s significant. Therefore, the number has 6
significant figures.
(D) 0.0010010 - The leading zeros are not significant, but the three zeros within and at the end of the
number are significant because they are between significant digits or at the end of the number after the
decimal. Therefore, this number has 5 significant figures.
2024
Given List I and List II, the correct matching based on the explanation of significant figures is as follows:
Option A
(A) - II (1001 has 4 significant figures)
(B) - I (010.1 has 3 significant figures)
(C) - IV (100.100 has 6 significant figures)
(D) - III ( 0.0010010 has 5 significant figures)
Thus, the correct answer is Option A.
Q2: 10 divisions on the main scale of a Vernier calliper coincide with 11 divisions on the Vernier scale.
If each division on the main scale is of 5 units, the least count of the instrument is :
(a)
?? ????
(b)
????
????
(c)
????
????
(d)
?? ?? [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
The least count of a Vernier caliper is the smallest measurement that can be obtained with it and is
determined by the difference in the measurement of one main scale division and one Vernier scale
division.
In this case, 10 divisions on the main scale coincide with 11 divisions on the Vernier scale. This means
that 11 divisions on the Vernier scale are equal in length to 10 divisions on the main scale. Since each
division on the main scale is 5 units, this is equal to:
10 divisions on main scale × 5 units per division = 50 units
The length of 10 divisions on the main scale (or 50 units) is therefore equal to the length of 11 divisions
on the Vernier scale. This means that:
1 division on the Vernier scale =
50 units
11
Therefore, the least count of the Vernier caliper, which is the difference between one division on the
main scale and one division on the Vernier scale, can be calculated as follows:
Least count = value of one main scale division - value of one Vernier scale division
Least count = 5 units -
50 units
11
Least count =
55 units
11
-
50 units
11
Least count =
5 units
11
Thus, the least count of the Vernier caliper is
5 units
11
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