Light (Part -1)

According to the law of reflection:

1. The angle of incidence ($i$) is equal to the angle of reflection (r).

   i=r

2. Both the incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence lie in the same plane.

Sun appears red at sunrise and sunset due to scattering of light — specifically, Rayleigh scattering.

Explanation:

• During sunrise and sunset, sunlight passes through a larger thickness of the Earth's atmosphere.

• Shorter wavelengths (blue and violet) scatter more and are removed from the direct path.

• Longer wavelengths (red and orange) pass through and reach the observer’s eyes, making the Sun appear red.

A converging lens is also known as a convex lens.

• It is thicker in the middle and thinner at the edges, and it causes parallel rays of light to bend inward and meet (converge) at a single point called the focus (or focal point).

Stars emit light based on their temperature, following blackbody radiation principles.

The color you see corresponds to the peak wavelength of emitted light, which shifts with temperature.

Based on Wien’s Displacement Law,

• hotter objects emit light at shorter wavelengths (bluer light),
• while cooler ones emit at longer wavelengths (redder light).

• The photometer makes an accurate comparison of the intensity of light received from different sources.

The glittering of air bubbles rising through water is caused by the process of total internal reflection.

Explanation:

• Light entering the air bubble from water undergoes multiple internal reflections inside the bubble, making it sparkle or glitter as it rises.

Light changes speed when it enters a different medium:

• From air to water/glass → light slows down → bends toward the normal.
• From water/glass to air → light speeds up → bends away from the normal.

Examples

• A pencil appears bent in a glass of water.
• Lenses in glasses or cameras focus light via refraction.
• Rainbows form due to refraction in raindrops.

Light slows down when it enters a medium denser than a vacuum (or air). The denser the medium, the slower light travels.

It is a transparent material with a refractive index (1.53) almost equal to that of crown glass.