Question

Cunoscand ca o lanterna cu o baterie de 4,5 V si rezistenta interna de 1 Ohm are randamentul de 95% sa se determine rezistenta becului si intensitatea curentului electric.

Answer 1

   
[tex]\displaystyle\\ \eta = \frac{R}{R+r}=95\% \\\\ \frac{R}{R+r}=0,95\\\\ R = 0,95(R+r)\\\\ R = 0,95R+0,95r\\\\ R - 0,95R = 0,95r\\\\ 0,05R = 0,95r\\\\ R = \frac{0,95r}{0,05} ~~~\text{unde: } r= 1~\Omega \\\\ R = \frac{0,95\times 1}{0,05} = \frac{95}{5} = \boxed{19~\Omega } \\\\\\ I = \frac{E}{R+r} = \frac{4,5}{19+1} = \frac{4,5}{20} = \boxed{0,225~A} = \boxed{225~mA}[/tex]