4 items
A wire spiral is connected to an ideal constant-voltage mains source with voltage $V$.
The circuit in Fig.
A luminous object is placed on the optical axis of a thin converging lens $\text{Л}_1$ with focal length $F$.
The optical element is a thin converging lens with focal length $f = 50\ \text{cm}$ and diameter $d = 5\ \text{cm}$.