A ray of light can undergo both reflection and refraction - Leaving Cert Physics - Question 8 - 2014

1. The incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.
2. The angle of incidence is equal to the angle of reflection, stated as ( \theta_i = \theta_r ).

An application of reflection of light can be seen in optical instruments such as mirrors, telescopes, and cameras, where the principles of reflection are utilized to direct and focus light.

To demonstrate the law of reflection, you can conduct the following experiment:

Apparatus:

• Mirror
• Rays of light (using a torch or laser)
• Protractor

Procedure:

1. Place the mirror on a flat surface and position it vertically.
2. Use a protractor to measure the angle of incidence by directing a ray of light at the mirror.
3. Mark the incident ray and reflected ray on the surface.
4. Measure the angles using the protractor. You should find that the angle of incidence is equal to the angle of reflection, confirming the law of reflection.

Refraction of light is the bending of light rays as they pass from one medium to another with a different density. It occurs due to a change in the speed of light in different media. This bending can be observed when light travels from air into glass or water. The angle of refraction changes based on the incident angle and the refractive indices of the involved media.

The special name given to the angle of incidence when the effect shown occurs is the 'critical angle.' This is the angle of incidence above which total internal reflection occurs and light cannot pass into the second medium.

To calculate the refractive index, we use the formula:

$n = \frac{\sin{\theta_i}}{\sin{\theta_r}}$

Given that ( \theta_i = 38° ) and assuming ( \theta_r = 90° ) (as it is typical for refraction into air), we can find:

Using the sine values: (n = \frac{\sin{38°}}{\sin{90°}} = \frac{0.6157}{1} = 0.6157$. Thus, the refractive index of the glass is approximately 1.62.

The diagram should illustrate:

1. The ray of light striking the boundary between air and glass at an increased angle of incidence of 40°.
2. The normal line at the boundary.
3. The refracted ray bending away from the normal as it exits the glass into the air.

The angle of refraction should be calculated to demonstrate that it is greater than that at 38°.