Question

How can we arrange a lens such a two beams makes parallel beams of light rays?​

Answer 1

This experiment requires two converging lenses so that the light beams passing through them become parallel beams of light rays.

So, we place two converging lenses, keeping a distance of d cm between them;

and, α = $f_1 + f_2$, in which $f_1$ and $f_2$ are the focal lengths of the respective lenses.

Then, the parallel light beams passing through the first lens will continue in its parallel path after moving from within the second lens.

The diagram has been attached below.

Answer 2

If we place two converging lens d cm apart, and α = f₁ +f₂   are focal length of both the lens then a parallel beam of light becomes parallel after passing through two lenses.

Explanation:

Refraction Rule for a Converging Lens

Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.

• Now suppose that the rays of light are traveling through the focal point on the way to the lens. These rays of light will refract when they enter the lens and refract when they leave the lens.
• As the light rays enter into the more dense lens material, they refract towards the normal; and as they exit into the less dense air, they refract away from the normal.
• These specific rays will exit the lens traveling parallel to the principal axis

Refraction Rules for a Converging Lens

Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.

Any incident ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.