8.3.22 | правка #20103 | Решения Савченко

Statement

8.3.22. When studying the dependence of the photocell current on its illumination, a microammeter is used, the scale of which is not enough for measurements. To double the current measurement limits, a corresponding shunt is connected to the microammeter. After that, under the same light of the photocell, not only the deviation of the arrow of the device changed, but also the current itself. Explain why, and confirm your explanation with a calculation. Photocell for continuous operation. In the case of continuous lighting, it can be considered a voltage generator or a current generator with fixed parameters.

Solution

Let $$r$$ be the resistance of the ammeter. To double the measurement range of the meter, a shunt with resistance $$r$$ must be connected in parallel with the meter so that half of the measured current is diverted to the shunt. The meter and the shunt together has resistance $$r/2$$ . Suppose that the photocell is a voltage generator $$V$$ and is connected to the load $$R$$ . Without the shunt, the measured current is $$V/(R+r)$$ . With the shunt, the measured current becomes $$V/(R+r/2)$$ .

Answer

See the solution.