The ray of light appears to diverge from the principal focus located on the same side of the lens.

The ray of light converges and passes through the principal focus on the other side of the convex lens.

Lenses with small apertures and where the two centres of curvature are equidistant from the optical centre are referred to as thin lenses. The discussion in this chapter is specifically limited to the behavior of such thin lenses.

In a series circuit, the current (I) remains constant throughout. The current through each resistor in the series is also equal to the total current flowing through the circuit. This is a fundamental characteristic of series circuits.