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A cell of internal resistance r supplies current to a 6.0Ω resistor and its effic...


Question

A cell of internal resistance r supplies current to a 6.0Ω resistor and its efficiency is 75%. Find the value of r.

Options

A) 4.5Ω

B) 1.0Ω

C) 8.0Ω

D) 2.0Ω


The correct answer is D.

Explanation:

Efficiency = power out put/power input * 100/1
= power out put/ power + that due * 100/1
to internal resistance
=> 75/1 = 12R *100/1
12(R+r)
i.e 75/100 = 6/6+r => 75 (6+r) = 100/*6
i.e 450 + 75r = 600
75r =600 - 450
i.e r = 150/75 = 2Ω
i.e r = 2Ω

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Dicussion (1)

  • Efficiency = power out put/power input * 100/1
    = power out put/ power + that due * 100/1
    to internal resistance
    => 75/1 = 12R *100/1
    12(R+r)
    i.e 75/100 = 6/6+r => 75 (6+r) = 100/*6
    i.e 450 + 75r = 600
    75r =600 - 450
    i.e r = 150/75 = 2Ω
    i.e r = 2Ω

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