arthham

JEE Advanced 1988 · Units and Measurements

In the formula X=3YZ2X = 3YZ^{2}, XX and ZZ have dimensions of capacitance and magnetic induction respectively. The dimensions of YY in MKSQ system are __________, __________.

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Written solution

Step 1: Identify the given quantities and their relations.

The given formula is:

X=3YZ2X = 3YZ^{2}

Since 33 is a dimensionless constant, the dimensional formula for YY is:

[Y]=[X][Z]−2[Y] = [X][Z]^{-2}

Here, XX represents capacitance and ZZ represents magnetic induction.

Step 2: Determine the dimensions of capacitance XX.

Capacitance CC is defined as charge QQ divided by potential difference VV.

[X]=[C]=[Q][V][X] = [C] = \frac{[Q]}{[V]}

Since potential difference is work done per unit charge (V=WQV = \frac{W}{Q}):

[X]=[Q]2[W][X] = \frac{[Q]^{2}}{[W]}

Using the dimensions of work [W]=ML2T−2[W] = M L^{2} T^{-2}:

[X]=Q2ML2T−2[X] = \frac{Q^{2}}{M L^{2} T^{-2}} [X]=M−1L−2T2Q2[X] = M^{-1} L^{-2} T^{2} Q^{2}

Step 3: Determine the dimensions of magnetic induction ZZ.

Magnetic induction BB is derived from the magnetic force formula:

F=qvBF = q v B [Z]=[B]=[F][q][v][Z] = [B] = \frac{[F]}{[q][v]}

Using the dimensions of force [F]=MLT−2[F] = M L T^{-2} and velocity [v]=LT−1[v] = L T^{-1}:

[Z]=MLT−2Q⋅LT−1[Z] = \frac{M L T^{-2}}{Q \cdot L T^{-1}} [Z]=MT−1Q−1[Z] = M T^{-1} Q^{-1}

Step 4: Calculate the dimensions of YY.

Substitute the dimensions of [X][X] and [Z][Z] into the relation [Y]=[X][Z]−2[Y] = [X][Z]^{-2}.

[Y]=(M−1L−2T2Q2)(MT−1Q−1)−2[Y] = \left(M^{-1} L^{-2} T^{2} Q^{2}\right) \left(M T^{-1} Q^{-1}\right)^{-2} [Y]=M−1−2L−2T2+2Q2+2[Y] = M^{-1-2} L^{-2} T^{2+2} Q^{2+2} [Y]=M−3L−2T4Q4[Y] = M^{-3} L^{-2} T^{4} Q^{4}

Answer: M−3L−2T4Q4M^{-3} L^{-2} T^{4} Q^{4}

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