JEE Main Previous Year Questions (2021-2025): Units & Measurements | Physics for JEE Main & Advanced PDF Download

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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