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A Wheatstone bridge has arms AB = 100 $\Omega$, BC = 10 $\Omega$, CD = 5 $\Omega$, DA = 60 $\Omega$. Is the bridge balanced for these values?
AYes, because all four resistances are different
BYes, because the opposite arms are equal
CNo, because $\dfrac{100}{60} \neq \dfrac{10}{5}$
DNo, because the total resistance is not 175 $\Omega$
Answer & Solution
Correct answer: C. No, because $\dfrac{100}{60} \neq \dfrac{10}{5}$
1. Balance requires the ratio of adjacent arms on each side to be equal.
2. Check $AB/DA = 100/60 = 1.67$ against $BC/CD = 10/5 = 2$.
3. Since $1.67 \neq 2$, the bridge is not balanced and a galvanometer current flows.
4. So C; having unequal or summed resistances (A, B, D) is not the balance test.
_Source: NCERT Class 12 Physics Ch 3 "Current Electricity", p.20_
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