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A student performs meter bridge experiment to determine specific resistance of a conducting wire of length 10cm and diameter 1mm. When a standard `6 Omega` resistance is connected on left gap and the given conducting wire is connected on the right gap, the balance points obtained for 60cm length of the meter bridge wire. The specific resistance in `Omega-m` for material of the given wire is:

A

`3.14 xx 10^(-2)`

B

`6.28 xx 10^(-2)`

C

`3.14 xx 10^(-5)`

D

`6.28 xx 10^(-5)`

Text Solution

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To determine the specific resistance (ρ) of a conducting wire using the meter bridge experiment, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding the Setup**: - We have a meter bridge where a standard 6 Ω resistance is connected on the left gap and a conducting wire of length 10 cm and diameter 1 mm is connected on the right gap. - The balance point is obtained at 60 cm on the meter bridge. 2. **Using the Meter Bridge Formula**: - The balance condition of the meter bridge is given by the formula: \[ \frac{R_1}{R} = \frac{L_1}{L} \] - Where: - \( R_1 \) is the resistance on the left (6 Ω), - \( R \) is the resistance of the wire, - \( L_1 \) is the length of the bridge wire on the left (60 cm), - \( L \) is the total length of the bridge wire (100 cm). 3. **Calculating the Resistance of the Wire**: - From the balance condition, we can rearrange the formula to find \( R \): \[ R = \frac{L}{L_1} \times R_1 \] - Substituting the values: \[ R = \frac{100 \, \text{cm}}{60 \, \text{cm}} \times 6 \, \Omega = \frac{100}{60} \times 6 = \frac{10}{6} \times 6 = 10 \, \Omega \] 4. **Finding the Specific Resistance**: - The resistance of a wire is given by the formula: \[ R = \rho \frac{L}{A} \] - Where: - \( \rho \) is the specific resistance, - \( L \) is the length of the wire (10 cm = 0.1 m), - \( A \) is the cross-sectional area of the wire. - The cross-sectional area \( A \) for a wire with diameter \( d \) is calculated as: \[ A = \frac{\pi d^2}{4} \] - Given that the diameter \( d = 1 \, \text{mm} = 1 \times 10^{-3} \, \text{m} \): \[ A = \frac{\pi (1 \times 10^{-3})^2}{4} = \frac{\pi \times 10^{-6}}{4} = \frac{3.14 \times 10^{-6}}{4} \approx 7.85 \times 10^{-7} \, \text{m}^2 \] 5. **Substituting Values to Find \( \rho \)**: - Rearranging the resistance formula to find \( \rho \): \[ \rho = R \frac{A}{L} \] - Substituting the known values: \[ \rho = 10 \, \Omega \times \frac{7.85 \times 10^{-7} \, \text{m}^2}{0.1 \, \text{m}} = 10 \times 7.85 \times 10^{-6} \, \Omega \cdot \text{m} = 7.85 \times 10^{-5} \, \Omega \cdot \text{m} \] 6. **Final Result**: - The specific resistance of the material of the given wire is approximately: \[ \rho \approx 7.85 \times 10^{-5} \, \Omega \cdot \text{m} \]
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