Physics

Determining the Focal Length and Radius of Curvature through the Reflection of Light Beams in Different Types of Mirrors

Joanna Abalos, Raechelle Daysa , Sharmaine Esquilona, Pauline Mariano, *Jerik Rola

University of the Philippines- Baguio

Governor Pack Road, Baguio City

*jcqr1995@hotmail.com

Abstract

The aim of this experiment is for the students to determine the focal length and radius of curvature of different types of mirrors. Also, the students should be able to show a visual representation of the reflection off plane and curved mirrors. This was done by using a light source and a silver-coated mirror with three facets- the plane, concave and convex. Incoming and outgoing rays along with the normal, incident and reflected rays were traced and indicated. At the end of the experiment, it was found that reflection obeys the law of reflection and the focal length and radius of curvature were determined.

1.Introduction

Reflection is a phenomenon that occurs when a ray of light strikes a surface and the direction of the ray is changed1. Light always follows the law of reflection, whether the surface is plane or curved. In this experiment, silver-coated mirror was used due to its high reflectivity2.

The law of reflection states that the angle of incidence is equal to the angle of reflection2. Curved mirrors, which use cylindrical lenses makes use of the centre of curvature to determine their focal length and they follow the equation:

f= r/2 (eq. 1)

where r: radius of curvature and f: focal length

Mirrors and the concept of reflection are used widely; examples of the uses of mirrors include telescopes, lasers, cameras and other equipment that uses lenses. Convex lenses are often used in rear view mirrors of vehicles and in shops to monitor for thieves because they take in a wide field of view while concave lenses are used in cosmetic mirrors2. To better understand its uses, reflection is studied in this experiment. The image produced (real...