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Units and Measurements · Question 13

JEE Main 2026 (Online) 2nd April Morning ShiftMCQMedium📈 Topic in 29% papers+4−1
1

The diameter of a wire measured by a screw gauge of least count 0.001 cm is 0.08 cm. The length measured by a scale of least count 0.1 cm is 150 cm. When a weight of 100 N is applied to the wire, the extension in length is 0.5 cm, measured by a micrometer of least count 0.001 cm. The error in the measured Young's modulus is 109 N/m2. The value of is . (Ignore the contribution of the load to Young's modulus error calculation)

  1. 1.3
  2. 1.65
  3. 0.13
  4. 0.25

Answer

(2) 1.65

Solution

Y= F/A l/L= 4FL d2 l

Data in SI: F=100 N, L=1.5 m, d=0.08 cm=8 10-4 m, l=0.5 cm=5 10-3 m

Y= 4 100 1.53.1416 (8 10-4)2 5 10-3

= 6001.005 10-8

5.97 1010 N/m2

Fractional error (load ignored):

YY=2 dd+ LL+ ( l) l

=2 0.0010.08+ 0.1150+ 0.0010.5

=0.025+0.00067+0.002=0.02767

Y=0.02767 5.97 1010

1.65 109 N/m2

=1.65

Answer: (2)

JEE Main 2026 (Online) 2nd April Morning Shift

Keep practising — Units and Measurements

2

Dimensions of universal gravitational constant (G) in terms of Planck's constant (h), distance (L), mass (M) and time (T) are .

  1. [ hTLM-2 ]
  2. [ hT-1LM-2 ]
  3. [ hTL2M-2 ]
  4. [ h-1T-1LM-2 ]
JEE Main 2026 (Online) 2nd April Evening Shift
3

In a screw gauge the zero of main scale reference line coincides with the fifth division of the circular scale when two studs are in contact. There are 100 divisions in circular scale and pitch of screw gauge is 0.1 mm. When diameter of a sphere is measured, the reading of main scale is 5 mm and 50th division of circular scale coincides with the reference line of main scale. The diameter of sphere is mm.

  1. 5.045
  2. 5.055
  3. 5.450
  4. 5.550
JEE Main 2026 (Online) 2nd April Evening Shift
4

When both jaws of vernier callipers touch each other, zero mark of the vernier scale is right to zero mark of main scale, 4th mark on vernier scale coincides with certain mark on the main scale. While measuring the length of a cylinder, observer observes 15 divisions on main scale and 5th division of vernier scale coincides with a main scale division. Measured length of cylinder is mm. (Least count of Vernier calliper = 0.1 mm)

  1. 15.5
  2. 15.4
  3. 15.9
  4. 15.1
JEE Main 2026 (Online) 28th January Morning Shift
5

The time period of a simple harmonic oscillator is T = 2 mk. Measured value of mass (m) of the object is 10 g with an accuracy of 10 mg and time for 50 oscillations of the spring is found to be 60 s using a watch of 2 s resolution. Percentage error in determination of spring constant (k) is %.

  1. 3.43
  2. 7.60
  3. 3.35
  4. 6.76
JEE Main 2026 (Online) 28th January Evening Shift
6

Match List - I with List - II. Choose the correct answer from the options given below :

  1. A-I, B-II, C-IV, D-III
  2. A-IV, B-III, C-I, D-II
  3. A-IV, B-I, C-II, D-III
  4. A-I, B-III, C-II, D-IV
JEE Main 2026 (Online) 28th January Evening Shift
7

In an experiment, a set of readings are obtained as follows: 1.24 mm, 1.25 mm, 1.23 mm, 1.21 mm. The expected least count of the instrument used in recording these readings is mm.

  1. 0.01
  2. 0.05
  3. 0.001
  4. 0.1
JEE Main 2026 (Online) 28th January Evening Shift
8

Match the LIST-I with LIST-II Choose the correct answer from the options given below:

  1. A-III, B-IV, C-II, D-I
  2. A-I, B-III, C-IV, D-II
  3. A-IV, B-III, C-I, D-II
  4. A-III, B-IV, C-I, D-II
JEE Main 2026 (Online) 24th January Morning Shift
9

In a vernier callipers, 50 vernier scale divisions are equal to 48 main scale divisions. If one main scale division = 0.05 mm, then the least count of the vernier callipers is mm.

  1. 0.002
  2. 0.02
  3. 0.05
  4. 0.005
JEE Main 2026 (Online) 24th January Evening Shift
10

In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal pitch line when their metallic studs are brought in contact. Using this instrument thickness of a sheet is measured. If pitch scale reading is 1 mm and the circular scale reading is 51 then the correct thickness of the sheet is mm. [Assume least count is 0.01 mm]

  1. 1.54
  2. 1.50
  3. 1.51
  4. 1.48
JEE Main 2026 (Online) 23rd January Morning Shift
11

Four persons measure the length of a rod as 20.00 cm, 19.75 cm, 17.01 cm and 18.25 cm. The relative error in the measurement of average length of the rod is :

  1. 0.18
  2. 0.24
  3. 0.06
  4. 0.08
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