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QJEEM20Ph7de3: JEE Main 2020 Physics - Class 12 JEEM20Ph7de3 Solution: In a meter bridge experiment S is a standard resistance. R is a …

In a meter bridge experiment S is a standard resistance. R is a resistance wire. It is found that balancing length is ll = 25 cm. If R is replaced by a wire of half length and half diameter that of R of same material, then the balancing distance l′l' (in cm) will now be________. JEE Main 2020 (Online) 9th January Evening Slot Physics - Current Electricity Question 221 English

Step-by-Step Verified Solution

SR=7525{S \over R} = {{75} \over {25}} = 3

R = ρLA{{\rho L} \over A} = 4ρLπd2{{4\rho L} \over {\pi {d^2}}}

R' = 4ρ(L2)π(d2)2{{4\rho \left( {{L \over 2}} \right)} \over {\pi {{\left( {{d \over 2}} \right)}^2}}} = 2R

Then SR′=100−ll{S \over {R'}} = {{100 - l} \over l}

⇒\Rightarrow 100−ll{{100 - l} \over l} = S2R{S \over {2R}} = 32{3 \over 2}

⇒\Rightarrow ll = 40 cm

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