Grade 7 ↓
Lighting and Optics
Light is a form of energy that travels in waves. It is what enables us to see the world around us. Light comes from various sources such as the sun, bulbs and candles. The study of light and its behaviour is called optics.
Nature of light
Light behaves like both a wave and a particle. When we see light as a wave, it travels in straight lines and can reflect or refract. As a particle, light is made up of tiny packets of energy called photons.
Wave properties of light
Light waves are similar to ripples on water. They have crests (highest points) and troughs (lowest points). The distance between two successive crests or troughs is called the wavelength, usually measured in nanometers (nm).
Wavelength (λ) = distance between two crests or troughs
Another important property of light is frequency. Frequency is the number of waves passing a point in one second. It is measured in Hertz (Hz).
Frequency (f) = number of waves per second
The speed of light is incredibly fast. In a vacuum, light travels at approximately this speed:
Speed of light (c) = 300,000 km/second or 3.0 x 10^8 m/second
Reflection of light
Reflection occurs when light bounces off a surface. You see your reflection in a mirror because light bounces off your face and bounces back into your eyes. There are two types of reflection: regular and diffuse.
- Regular reflection: This occurs on smooth surfaces like mirrors, where light reflects in a specific direction.
- Diffuse reflection: This occurs on a rough surface like paper, where light scatters in many directions.
The angle at which light falls on a surface is called the angle of incidence. The angle at which light reflects is called the angle of reflection. These angles are always equal. This is called the law of reflection:
Angle of incidence = Angle of reflection
Refraction of light
Refraction is the bending of light as it passes from one medium to another. For example, when light enters water from air, it slows down and bends. This is why a straw looks bent when you look at it half in and half out of a glass of water.
Lenses and their effects
Lenses are pieces of glass or other transparent materials that can bend light. They are used in eyeglasses, cameras, and microscopes. There are two main types of lenses: convex and concave.
- Convex lens: Thicker in the middle than at the edges. It brings the light rays together, called a converging lens.
- Concave lens: Thinner in the middle than at the edges. It spreads light rays apart, called a diverging lens.
An example of a convex lens is a magnifying glass. It converges light rays to a point, called the focal point. The distance from the lens to the focal point is the focal length.
Color of light
White light is made up of individual colors. When light passes through a prism, it is split into a spectrum of colors. This is similar to the way a rainbow is formed:
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Purple
Each colour has a different wavelength, with red colour having the longest wavelength and violet colour having the shortest wavelength.
Red: 620-750nm
Violet: 380–450 nm
Eyes and vision
Our eyes are like cameras that capture light and send signals to our brain, helping us see. The main parts of the eye include the cornea, lens, retina and optic nerve. Light enters through the cornea, passes through the lens and is focused on the retina, which sends information to the brain.
Applications of optics
Optics has many applications. Here are some examples:
- Glasses and contact lenses: Help people with vision problems see clearly.
- Camera: Capture images by focusing light onto the sensor or film.
- Telescopes: These allow us to see distant objects in space.
- Microscope: Used to observe minute details of small objects.
Conclusion
Light and optics are fascinating topics in physics. They help us understand how light behaves and how we can use it in everyday life. By studying light, reflection, refraction, and lenses, we learn more about the world as well as develop useful tools and techniques.
Comments