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Units and Measurements question

2024 · 6 Apr · Shift 1 · Q69
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Units and Measurements question

2024 · 6 Apr · Shift 1 · Q69

JEE MainPhysicsUnits and MeasurementsMCQ+4 / −1

Match List I with List II

LIST I LIST II
A. Torque I.
[M1L1T−2A−2]\left[M^1 L^1 T^{-2} A^{-2}\right][M1L1T−2A−2]
B. Magnetic field II.
[L2A1]\left[L^2 A^1\right][L2A1]
C. Magnetic moment III.
[M1T−2A−1]\left[M^1 T^{-2} A^{-1}\right][M1T−2A−1]
D. Permeability of free space IV.
[M1L2T−2]\left[M^1 L^2 T^{-2}\right][M1L2T−2]

Choose the correct answer from the options given below:

  1. A
    A-I, B-III, C-II, D-IV
  2. B
    A-IV, B-II, C-III, D-I
  3. C
    A-III, B-I, C-II, D-IV
  4. D
    A-IV, B-III, C-II, D-I
View written solutionFree

Correct answer: D

  1. Find dimensions of each quantity in List I

We match each physical quantity with its dimensional formula.


  1. A. Torque

Torque =Force×distance= \text{Force} \times \text{distance}=Force×distance

Since, [Force]=[M1L1T−2][\text{Force}] = [M^1L^1T^{-2}][Force]=[M1L1T−2]

Therefore, [τ]=[M1L1T−2]⋅[L]=[M1L2T−2][\tau] = [M^1L^1T^{-2}]\cdot [L] = [M^1L^2T^{-2}][τ]=[M1L1T−2]⋅[L]=[M1L2T−2]

So, A→IVA \to IVA→IV


  1. B. Magnetic field

Using Lorentz force, F=qvBF = qvBF=qvB

So, B=FqvB = \frac{F}{qv}B=qvF​

Now,

  • [F]=[M1L1T−2][F] = [M^1L^1T^{-2}][F]=[M1L1T−2]
  • [q]=[AT][q] = [AT][q]=[AT]
  • [v]=[LT−1][v] = [LT^{-1}][v]=[LT−1]

Hence, [B]=[M1L1T−2][AT][LT−1][B] = \frac{[M^1L^1T^{-2}]}{[AT][LT^{-1}]}[B]=[AT][LT−1][M1L1T−2]​

[B]=[M1T−2A−1][B] = [M^1T^{-2}A^{-1}][B]=[M1T−2A−1]

So, B→IIIB \to IIIB→III


  1. C. Magnetic moment

Magnetic moment of a current loop, μ=I×area\mu = I \times \text{area}μ=I×area

Thus, [μ]=[A]⋅[L2]=[L2A1][\mu] = [A]\cdot [L^2] = [L^2A^1][μ]=[A]⋅[L2]=[L2A1]

So, C→IIC \to IIC→II


  1. D. Permeability of free space

From magnetic force between two long parallel wires, FL=μ0I1I22πr\frac{F}{L} = \frac{\mu_0 I_1 I_2}{2\pi r}LF​=2πrμ0​I1​I2​​

So, μ0=FL⋅rI2\mu_0 = \frac{F}{L}\cdot \frac{r}{I^2}μ0​=LF​⋅I2r​

Now, [FL]=[M1T−2]\left[\frac{F}{L}\right] = [M^1T^{-2}][LF​]=[M1T−2]

Multiplying by rrr: [M1T−2]⋅[L]=[M1L1T−2][M^1T^{-2}]\cdot [L] = [M^1L^1T^{-2}][M1T−2]⋅[L]=[M1L1T−2]

Dividing by [A2][A^2][A2]: [μ0]=[M1L1T−2A−2][\mu_0] = [M^1L^1T^{-2}A^{-2}][μ0​]=[M1L1T−2A−2]

So, D→ID \to ID→I


  1. Final matching

Thus the correct match is:

  • A→IVA \to IVA→IV
  • B→IIIB \to IIIB→III
  • C→IIC \to IIC→II
  • D→ID \to ID→I

This corresponds to Option D.


  1. Comparison with stored answer

Stored correct answer = D

Our derived answer = D

So, the answer agrees with the stored answer.

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