Question 1

What is the thin lens equation?

Accepted Answer

The thin lens equation is 1/f = 1/do + 1/di, where f is the focal length, do is the object distance, and di is the image distance. A converging lens with f = 10 cm and an object at do = 15 cm produces an image at di = 30 cm (a real, inverted, magnified image). Positive di means a real image; negative di means a virtual image.

Question 2

What is Snell's law and how is it used?

Accepted Answer

Snell's law describes how light bends when passing between materials: n1 sin(theta1) = n2 sin(theta2). When light goes from air (n = 1.00) into glass (n = 1.50) at 30 degrees, it refracts to sin(theta2) = sin(30) / 1.50, giving theta2 = 19.5 degrees. Light bends toward the normal when entering a denser medium and away from the normal when entering a less dense medium.

Question 3

How do you calculate magnification?

Accepted Answer

Magnification equals the negative ratio of image distance to object distance: M = -di/do. A magnification of -2 means the image is twice the size of the object and inverted. Positive magnification means the image is upright (virtual), while negative magnification means it is inverted (real). For a magnifying glass held close to an object, M is positive and greater than 1.

Question 4

What is total internal reflection?

Accepted Answer

Total internal reflection occurs when light traveling in a denser medium hits the boundary at an angle greater than the critical angle, causing all light to reflect back instead of refracting. The critical angle is found using sin(theta_c) = n2/n1. For glass to air, theta_c = arcsin(1.00/1.50) = 41.8 degrees. This principle enables fiber optic cables to transmit light over long distances with minimal loss.

Question 5

What is the difference between converging and diverging lenses?

Accepted Answer

Converging (convex) lenses are thicker in the middle and bring parallel light rays together at a focal point. They can form real or virtual images depending on object position. Diverging (concave) lenses are thinner in the middle and spread light rays apart, always producing virtual, upright, reduced images. Converging lenses have positive focal lengths; diverging lenses have negative focal lengths.

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