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NEET2018PhysicsCurrent ElectricityActual

A set of n equal resistances, of value R each, are connected in series to a battery of emf E and internal resistances R . The current drawn is I . Now, the n resistance are connected in parallel to the same battery. Then the current drawn from battery becomes 10 I . The value of n is

Options

  1. A20
  2. B11
  3. C10
  4. D9

Correct answer

C. 10

Step-by-step solution

In the first case, it is given that 'n' resistances are arranged in series, each having a resistance R . In that case, the nett reistance of the external circuit is ' nR '. The internal resistance itself is R . Hence, the resultant resistance of the circuit is n R + R = ( n + 1 ) R . ∵ I =   ε n R + R ⇒ I = E ( n + 1 ) R .... (i) In the case of parallel combination, these external n resistances are arranged in parallel,thereby their nett external resistance is R n . This is in

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