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Electromagnetic Induction question

2006 · Shift 0 · Q92
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Electromagnetic Induction question

2006 · Shift 0 · Q92

JEE MainPhysicsElectromagnetic InductionMCQ+4 / −1
Which of the following units denotes the dimension ML2Q2{{M{L^2}} \over {{Q^2}}}Q2ML2​, where QQQ denotes the electric charge?
  1. A
    Wb/m2Wb/{m^2}Wb/m2
  2. B
    Henry (H)(H)(H)
  3. C
    H/m2H/{m^2}H/m2
  4. D
    Weber (Wb)(Wb)(Wb)
View written solutionFree

Correct answer: B

  1. Given dimension

We need the unit corresponding to ML2Q2\frac{M L^2}{Q^2}Q2ML2​ where QQQ is electric charge.

Since electric charge has dimension [Q]=[IT],[Q] = [IT],[Q]=[IT], we get ML2Q2=ML2I2T2.\frac{M L^2}{Q^2} = \frac{M L^2}{I^2 T^2}.Q2ML2​=I2T2ML2​.

  1. Now find the dimensions of each option

Option A: Wbm2\dfrac{Wb}{m^2}m2Wb​

We know 1 Wb=1 T⋅m21\,Wb = 1\,T\cdot m^21Wb=1T⋅m2 and tesla has dimension [T]=NA m=MLT−2IL=MT−2I−1.[T] = \frac{N}{A\,m} = \frac{M L T^{-2}}{I L} = M T^{-2} I^{-1}.[T]=AmN​=ILMLT−2​=MT−2I−1. So, [Wb]=[T][m2]=ML2T−2I−1.[Wb] = [T][m^2] = M L^2 T^{-2} I^{-1}.[Wb]=[T][m2]=ML2T−2I−1. Therefore, [Wbm2]=MT−2I−1.\left[\frac{Wb}{m^2}\right] = M T^{-2} I^{-1}.[m2Wb​]=MT−2I−1. This is not equal to ML2I2T2\dfrac{M L^2}{I^2 T^2}I2T2ML2​.

So, A is incorrect.


Option B: Henry (H)(H)(H)

Inductance is defined by V=LdIdtV = L\frac{dI}{dt}V=LdtdI​ so [L]=[V][t][I].[L] = \frac{[V][t]}{[I]}.[L]=[I][V][t]​. Now, [V]=[energy][charge]=ML2T−2IT=ML2T−3I−1.[V] = \frac{[\text{energy}]}{[\text{charge}]} = \frac{M L^2 T^{-2}}{I T} = M L^2 T^{-3} I^{-1}.[V]=[charge][energy]​=ITML2T−2​=ML2T−3I−1. Thus, [H]=(ML2T−3I−1)(T)I=ML2T−2I−2.[H] = \frac{(M L^2 T^{-3} I^{-1})(T)}{I} = M L^2 T^{-2} I^{-2}.[H]=I(ML2T−3I−1)(T)​=ML2T−2I−2. Since Q=ITQ = ITQ=IT, ML2T−2I−2=ML2Q2.M L^2 T^{-2} I^{-2} = \frac{M L^2}{Q^2}.ML2T−2I−2=Q2ML2​. So, B matches exactly.

Thus, B is correct.


Option C: Hm2\dfrac{H}{m^2}m2H​

Using [H]=ML2T−2I−2,[H] = M L^2 T^{-2} I^{-2},[H]=ML2T−2I−2, we get [Hm2]=MT−2I−2.\left[\frac{H}{m^2}\right] = M T^{-2} I^{-2}.[m2H​]=MT−2I−2. This is not equal to ML2I2T2\dfrac{M L^2}{I^2 T^2}I2T2ML2​.

So, C is incorrect.


Option D: Weber (Wb)(Wb)(Wb)

From above, [Wb]=ML2T−2I−1.[Wb] = M L^2 T^{-2} I^{-1}.[Wb]=ML2T−2I−1. This is not equal to ML2I2T2\dfrac{M L^2}{I^2 T^2}I2T2ML2​.

So, D is incorrect.

  1. Final answer

The required unit is Henry (H)\boxed{\text{Henry }(H)}Henry (H)​

  1. Comparison with stored correct answer

Stored correct answer: B

Our derived answer: B

So, the answer agrees with the stored correct answer.

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