7.
A physical quantity P is related to four observables a, b, c and d as
P-
[tex] \sqrt{ab \times} d {}^{a} \div \sqrt{c} [/tex]
ab.de (ais Constan!) The percentage errors is a, b, c and d are 0.5% in each. If
the percentage error in P is 2%, then a is
1)
5/2
2)
2/5
3)
3/4
4)
3/2

Answer :

Answer:

To find the value of \( a \), we need to analyze the given equation for the physical quantity \( P \) and calculate the percentage error.

### Given:

\[ P = \frac{\sqrt{ab} \cdot d^a}{\sqrt{c}} \]

The percentage errors in \( a \), \( b \), \( c \), and \( d \) are all 0.5%.

The percentage error in \( P \) is 2%.

### Step-by-Step Solution:

First, let's rewrite \( P \) in a more convenient form for error analysis.

\[ P = \frac{(ab)^{1/2} \cdot d^a}{c^{1/2}} \]

Taking the natural logarithm on both sides to make differentiation easier:

\[ \ln P = \ln \left( \frac{(ab)^{1/2} \cdot d^a}{c^{1/2}} \right) \]

Using logarithm properties:

\[ \ln P = \ln \left( (ab)^{1/2} \right) + \ln \left( d^a \right) - \ln \left( c^{1/2} \right) \]

\[ \ln P = \frac{1}{2} \ln (ab) + a \ln d - \frac{1}{2} \ln c \]

Further expanding the logarithms:

\[ \ln P = \frac{1}{2} (\ln a + \ln b) + a \ln d - \frac{1}{2} \ln c \]

Differentiating both sides to find the relative error:

\[ \frac{dP}{P} = \frac{1}{2} \left( \frac{da}{a} + \frac{db}{b} \right) + a \frac{dd}{d} - \frac{1}{2} \frac{dc}{c} \]

The relative errors of \( a \), \( b \), \( c \), and \( d \) are given as 0.5% each. Converting to decimal form for calculation:

\[ \frac{da}{a} = \frac{db}{b} = \frac{dc}{c} = \frac{dd}{d} = 0.005 \]

Substituting these into the error equation:

\[ \frac{dP}{P} = \frac{1}{2} (0.005 + 0.005) + a \cdot 0.005 - \frac{1}{2} \cdot 0.005 \]

Simplifying:

\[ \frac{dP}{P} = \frac{1}{2} \cdot 0.01 + a \cdot 0.005 - 0.0025 \]

\[ \frac{dP}{P} = 0.005 + 0.005a - 0.0025 \]

\[ \frac{dP}{P} = 0.0025 + 0.005a \]

Given the percentage error in \( P \) is 2% or 0.02 in decimal:

\[ 0.02 = 0.0025 + 0.005a \]

Solving for \( a \):

\[ 0.02 - 0.0025 = 0.005a \]

\[ 0.0175 = 0.005a \]

\[ a = \frac{0.0175}{0.005} \]

\[ a = 3.5 \]

Therefore, the value of \( a \) is:

\[ \boxed{3.5} \]

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Answer:

2)

2/5

Explanation:

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