The diagram shows a circuit with a cell and three resistors with resistances$\;{R_1}$, $\;{R_2}$ and $\;{R_3}$.
The cell has negligible internal resistance.
The total resistance of the circuit is $\;{R_T}$.
Which equation for $\;{R_T}$ is correct?

1 )
${R_T}{\text{ }} = {\text{ }}{R_1}{\text{ }} + {\text{ }}{R_2} = {\text{ }}A{\text{ }} + {\text{ }}{R_3}$
2 )
${R{_T}}{\text{ }} = {\text{ }}\frac{1}{{{R_1}{\text{ }} + {\text{ }}{R_2}}} = \frac{1}{{{R_3}}}$
3 )
$\frac{1}{{{R_T}}}{\text{ }} = {\text{ }}\frac{1}{{{R_1}{\text{ }} + {\text{ }}{R_2} + {R_3}}}$
$\frac{1}{{{R_T}}}{\text{ }} = {\text{ }}\frac{1}{{{R_1}{\text{ }} + {\text{ }}{R_2}}} + \frac{1}{{{R_3}}}$
تحلیل ویدئویی تست
تحلیل ویدئویی برای این تست ثبت نشده است!