The electric power P (in W) produced by a certain battery is given by: P= 49r/ (r+0.8)^2, where r is the resistance in the circuit. For what value of r is the power a maximum?

r = 1 Ohms

Explanation:

Given that:

P =

where r is the resistance in the circuit.

If r = 1 Ohms;

P =

  =

  =

  = 15.1235

P = 15.12 W

If r = 3 Ohms;

P =

  =

P   = 10.18 W

If r = 5 Ohms;

P =

  =

  = 7.230

P = 7.23 W

Therefore, the value of r for maximum power is 1 Ohms.

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