Дано:
$P_{1} = 25$ Вт;
$P_{2} = 40$ Вт;
$P_{3} = 60$ Вт;
$P_{4} = 100$ Вт;
U = 220 В.
Найти:
$R_{1}$ − ?
$R_{2}$ − ?
$R_{3}$ − ?
$R_{4}$ − ?
Решение:
P = UI;
$I = \frac{P}{U}$;
$R = \frac{U}{I} = \frac{U}{\frac{P}{U}} = \frac{U^{2}}{P}$;
$R_{1} = \frac{U^{2}}{P_{1}} = \frac{220^{2}}{25} = 1936$ Ом;
$R_{2} = \frac{U^{2}}{P_{2}} = \frac{220^{2}}{40} = 1210$ Ом;
$R_{3} = \frac{U^{2}}{P_{3}} = \frac{220^{2}}{60} = 807$ Ом;
$R_{4} = \frac{U^{2}}{P_{4}} = \frac{220^{2}}{100} = 484$ Ом.
Ответ: 1936 Ом; 1210 Ом; 807 Ом; 484 Ом.