7. In the electrical circuit shown in the figure, the resistances of the resistors are $R_{1}=1$ Ohm, $R_{2}=2$ Ohms, $R_{3}=3$ Ohms, and $R_{4}=4$ Ohms. Assume that the resistances of all diodes in the forward direction are negligibly small, and in the reverse direction are infinite. Determine the resistance of the entire circuit between points $A$ and $B$ in the situation where the negative pole of the current source is connected to point $A$, and the positive pole to point $B$. The resistance of the connecting wires is negligibly small. (10 points)

![](https://cdn.mathpix.com/cropped/2024_05_06_564114d217ece4a63410g-11.jpg?height=471&width=759&top_left_y=1249&top_left_x=657)
Answer: 2.38 $O m$

Solution. In the given situation, the following equivalent circuit is obtained $(2$ points $):$

![](https://cdn.mathpix.com/cropped/2024_05_06_564114d217ece4a63410g-11.jpg?height=323&width=805&top_left_y=2003&top_left_x=634)

Its total resistance: $R=\frac{R_{1} R_{2}}{R_{1}+R_{2}}+\frac{R_{3} R_{4}}{R_{3}+R_{4}}=\frac{1 \cdot 2}{1+2}+\frac{3 \cdot 4}{3+4}=\frac{50}{21} \approx 2.38$ Ohms (5 points).