Question

Stie cineva 18 ,19 , 20 sau 24 ? va rog frumos ? . explicatie pas cu pas daca se poate

Answer 1

18) rezistenta interioara=r

P ext = RE patrat/ (R+r) patrat

$p \: ext = \frac{5 {e}^{2} }{ {(5 + r)}^{2} }$

$p \: ext = \frac{0.2 {e}^{2} }{ {(0.2 + r)}^{2} }$

Egalam cele doua puteri exterioare:

$\frac{5 {e}^{2} }{ {(5 + r)}^{2} } = \frac{0.2 {e}^{2} }{ {(0.2 + r)}^{2} }$

${(5 + r)}^{2} \times 0.2 {e}^{2} = {(0.2 + r)}^{2} \times 5 {e}^{2}$

Impartim prin e patrat:

${(5 + r)}^{2} \times 0.2 = {(0.2 + r)}^{2} \times 5$

Impartim totul la 0.2:

${(5 + r)}^{2} = {(0.2 + r)}^{2} \times 25$

Desfacem parantezele:

${r}^{2} + 10r + 25 = ( {r}^{2} + 0.4r + 0.04) \times 25$

${r}^{2} + 10r + 25 = 25 {r}^{2} + 10r + 1$

-r patrat

10r+25=24r patrat+10r+1/-10r

25=24 r patrat+1/-1

24= 24 r patrat/ ÷24

r patrat = 1 => r= 1 ohm