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Question

The percentage error in the calculated volume of a sphere, if there is $2\%$ error in its diameter measurement, is _________.

The correct answer is
6

Sphere Volume Formula

The volume ($V$) of a sphere is given by the formula: $V = \frac{4}{3}\pi r^3$, where $r$ is the radius.

Volume Calculation Using Diameter

Since the radius ($r$) is half the diameter ($d$), $r = \frac{d}{2}$. Substituting this into the volume formula gives the volume in terms of diameter:

$V = \frac{4}{3}\pi \left(\frac{d}{2}\right)^3 = \frac{4}{3}\pi \frac{d^3}{8} = \frac{\pi}{6}d^3$.

This shows that the volume ($V$) is proportional to the cube of the diameter ($d^3$), meaning $V \propto d^3$.

Error Propagation Rule

When a quantity depends on a power of a variable, the percentage error propagates accordingly. If $V \propto d^n$, the relationship between the percentage errors is:

$ \frac{\Delta V}{V} \times 100\% = n \left( \frac{\Delta d}{d} \times 100\% \right) $

Percentage Error in Sphere Volume

In this problem, the volume depends on the cube of the diameter ($V \propto d^3$), so the exponent $n=3$. We are given the percentage error in the diameter measurement:

$ \frac{\Delta d}{d} \times 100\% = 2\% $

Now, we apply the error propagation rule:

$ \text{Percentage Error in Volume} = 3 \times (\text{Percentage Error in Diameter}) $

$ \frac{\Delta V}{V} \times 100\% = 3 \times (2\%) $

$ \frac{\Delta V}{V} \times 100\% = 6\% $

Final Volume Error

Therefore, the percentage error in the calculated volume of the sphere is $6\%$.

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