Some lenses are shaped with one flat side and one spherically-shaped side. This shape is designed to focus parallel light rays onto a single point. In a few sentences, explain how the spherical shape of the lens' surfaces causes parallel light rays to focus on a single point. (Assume the light is travelling through air into a lens with an index of refraction greater than that of air.) g

Some lenses are used to focus light to a pre-defined point based on the amount of curvature of their surfaces.

In a piano design convex, some surfaces are flat while others has positive lenses (biconvex)

Explanation:

Solution

These lenses are applied to pay attention to light in a  point pre-defined  based on the amount of curvature of their surfaces.

For that of a plano-convex design, one surface has a positive curve and for biconvex lenses, both surfaces are positively curved while the other  remains flat.

when used practically, plano-convex lenses are most commonly used where the object being imaged is far apart from lens.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.