Light

Properties of light

Light can be described as a stream of particles traveling in a wave-like pattern in a straight path. But unlike sound waves, it does not need a medium to travel. It can travel in a vacuum or through a medium like air or glass. Light waves are a form of electromagnetic radiation (that has both electric and magnetic fields around them) just like radio waves, microwaves, and x-rays. In simple word, light can be described in terms of –

1. PHOTONS – Photons are tiny elementary particles that are the basic units of all light. They carry and transmit light.
2. WAVES – Photons travel in waves and have peaks and valleys. The distance between the two peaks is called a wavelength. Light waves travel through space at a speed of approximately 3 x 10⁶ m/s.

Visible spectrum

Visible Light is composed of 7 different colors – violet, indigo, blue, green, yellow, orange and red (VIBGYOR). The color of the light depends on its wavelength. For example, violet color has the shortest wavelength and it increases with indigo, blue and so on, with red color having the longest wavelength. When light waves of all colors travel together, they appear white.

When white light is passed through a prism, the constituent waves bend by different amounts and we see the separated colors. This phenomenon is called dispersion. During the formation of a rainbow, each suspended droplet of water in the air acts as a prism giving us one of the most beautiful phenomena in nature.

How do we see an object?

An object is visible to us either because it gives off light or because it bounces off light that falls on it. The process of bouncing off light from the surface of an object is known as the REFLECTION of light. For example, the Sun gives off its own light, and hence it is visible to us. The Moon, on the other hand, is visible to us as it bounces off the light from the Sun that falls on it.

How do we see colors?

Objects are classified into opaque, translucent and transparent depending upon their behavior with light. An opaque object does not allow light to pass through it. It reflects most of the light that falls on it. When we look at a red apple, the wavelengths of the reflected light determine the color we see on it. Most of the wavelengths reflected in this case equal to that of the wavelength of the color red. These reflected parts of light reach our eyes and special cells present in them called cone cells. The cone cells detect them and send a signal to the brain, where it is processed and interpreted as RED.

When objects like glass or water do not reflect or absorb much light and allow most of the light to pass through it, it is known as transparent. Objects that allow some light to pass through it but are not completely see-through, are known as translucent. Some plastics, frosted, and stained glass are some examples.

Check Point

1. Objects that allow light to pass through them completely are known as _____.
2. A ______ can split white light into 7 constituent colored rays.
3. Name the three main components of sunrays.
4. Too much exposure to ____ rays can cause skin cancer.
5. The elementary particles that form the basic unit of light are known as ______.

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