Question

Difficulty: MediumPhysical Quantities, Units and Dimensions

The speed vv of a transverse wave traveling along a stretched string under tension TT with mass per unit length μ\mu is given by v=kTxμyv = k T^x \mu^y, where kk is a dimensionless constant. What is the numerical value of the exponent xx?

Answer: 0.5

Answer

The numerical value of the exponent xx is 0.5.
Applying the principle of dimensional homogeneity, the dimensions on both sides must match. Speed [v]=LT1[v] = L T^{-1}, tension force [T]=MLT2[T] = M L T^{-2}, and mass per unit length [μ]=ML1[\mu] = M L^{-1}. Substituting these into v=kTxμyv = k T^x \mu^y yields M0L1T1=Mx+yLxyT2xM^0 L^1 T^{-1} = M^{x+y} L^{x-y} T^{-2x}. Comparing the exponents of TT gives 2x=1-2x = -1, leading to x=0.5x = 0.5.

Step-by-Step Solution

1
Determine the dimensions of speed vv, tension force TT, and linear density μ\mu.
[v]=LT1[v] = L T^{-1}, [T]=MLT2[T] = M L T^{-2}, [μ]=ML1[\mu] = M L^{-1}
Tension is a force (F=maF=ma) with dimensions [MLT2][M L T^{-2}], and μ\mu is mass per unit length (m/lm/l) with dimensions [ML1][M L^{-1}].
2
Substitute the dimensional formulas into the equation v=kTxμyv = k T^x \mu^y and collect powers of base dimensions.
M0L1T1=Mx+yLxyT2xM^0 L^1 T^{-1} = M^{x+y} L^{x-y} T^{-2x}
Combining exponents for base dimensions MM, LL, and TT allows applying the principle of dimensional homogeneity.
3
Equate the exponent of TT on both sides to solve for xx.
2x=1    x=0.5-2x = -1 \implies x = 0.5
The exponent of TT on the left side is 1-1 and on the right side is 2x-2x.

Key Concept

Dimensional Analysis and Determination of Exponents
Estimated Time:1m 30s
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