Problem 3: Focusing Properties of a Lens (20 points) In class, we considered the

Question

Problem 3: Focusing Properties of a Lens (20 points) In class, we considered the ray picture to examine the propagation properties of electromagnetic radiation. Using this approach, suppose that we have a perfectly collimated beam of light that is normally incident on a lens of focal length, f At the focal point, what is the spot size (i.e. the beam diameter) of the beam? You must show how you arrived at your answer analytically a. b. Does the answer make physical sense? Why or why not? . What is it about the ray description of electromagnetic radiation that allows for this answer?

Explanation / Answer

A) At the focal point well collimated rays will form a point. The beam diameter essentially goes to zero.
As any ray parallel to the optical axis will end up on the focal point of a lens after refraction, and collimated rays are parallel to the optical axis, so all the rays meet at the focal point of the lens.

B) This answer makes sense. Collimated rays have plane wavefront, a point source at large distance can be approximated to have a plane wavefront. So when the collimated rays pass through the lens it creates an image of the source. in this case, a point.

C) According to the ray description of electromagnetic radiation rays always travel at a straight line. This description allows the collimated beam to meet at the focus and make an image of the approximated point source.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.