LIGHT

CloseWhen two mirrors are placed at an angle θ (theta) to each other, the number of images formed is (360/θ) − 1, provided 360/θ is an even number. If it is odd, the formula gives the number of images for symmetric placement of the object.

CloseUsing the formula (360 / angle) − 1 = (360 / 60) − 1 = 6 − 1 = 5 images. This is why a kaleidoscope or a mirror room creates many reflections of a single object.

CloseWhen two mirrors are exactly parallel, light keeps reflecting back and forth endlessly. Each reflection produces a new image, and theoretically the number of images is infinite. In practice, the images become dimmer and eventually disappear due to absorption of light.

CloseA kaleidoscope has two or three rectangular plane mirrors arranged in a triangle or V-shape inside a tube. Small coloured pieces of glass or plastic at one end are reflected many times, creating symmetrical and colourful patterns when the tube is rotated.

CloseRotating the kaleidoscope causes the small coloured objects at the end to tumble into new positions. The multiple reflections then create a new symmetrical pattern. Without rotation, the pattern remains the same.

CloseWhite sunlight is actually a mixture of seven colours: violet, indigo, blue, green, yellow, orange, and red (VIBGYOR). When these colours are mixed in the right proportions, they appear white to our eyes. A rainbow shows these colours separated.

CloseDispersion is the phenomenon where white light splits into its component colours when it passes through a transparent medium like a glass prism or water droplets in the air. Rainbows are formed by dispersion of sunlight by raindrops.

CloseThe iris is the coloured part of the eye (blue, brown, green, etc.). It has a hole in the centre called the pupil. The iris muscles contract or expand to make the pupil smaller or larger, thus controlling how much light enters the eye.

CloseThe pupil is the opening in the centre of the iris. It looks black because the inside of the eye is dark. In dim light, the pupil becomes larger to let in more light. In bright light, it becomes smaller to protect the retina.

CloseThe cornea is the clear, dome-shaped window at the very front of the eye. It helps focus light as it enters the eye. It has no blood vessels and gets oxygen directly from the air.

CloseThe eye lens is a soft, transparent, and flexible structure. It can change its shape (become thicker or thinner) to focus on objects at different distances. This ability is called accommodation.

CloseThe retina is a thin layer of tissue lining the back of the eye. It contains millions of light-sensitive cells (rods and cones) that convert light into electrical signals. These signals are sent to the brain via the optic nerve.

CloseRods are photoreceptor cells in the retina that work best in low light conditions. They do not detect colour; they only sense brightness and darkness. This is why in very dim light, we see only shades of grey, not colours.

CloseCones are photoreceptor cells that need bright light to function. They are responsible for colour vision. There are three types of cones: sensitive to red, green, and blue light. Together they allow us to see millions of colours.

CloseThe optic nerve is a bundle of more than one million nerve fibres. It carries visual information from the retina to the brain. The brain then interprets these signals as images. The point where the optic nerve leaves the retina has no light-sensitive cells; this creates the blind spot.

CloseWashing eyes with clean water removes dust and keeps them refreshed. Reading in dim light strains the eyes, rubbing with dirty hands can cause infection, and staring at the sun can permanently damage the retina.

CloseLooking at a distant object relaxes the ciliary muscles that control the eye lens. The 20-20-20 rule is often recommended: every 20 minutes, look at something 20 feet away for 20 seconds.

CloseRubbing can scratch the cornea. Washing with clean, cool water helps flush out the particle. If irritation continues, one should see a doctor. Never use unprescribed eye drops.

CloseBraille is a writing and reading system for people who are blind or have severe visual impairment. It uses raised dots that are felt with the fingertips. Each pattern of dots represents a letter, number, or punctuation.

CloseA standard Braille cell is a rectangle with two columns and three rows, making six possible positions. Different combinations of raised dots in these six positions represent different characters. There are 64 possible combinations (2 to the power 6).

CloseLouis Braille was a Frenchman who became blind after a childhood accident. At age 15, he developed the Braille system based on a military code called night writing. He published his system in 1829.

CloseLateral inversion is the swapping of left and right in a plane mirror image. For example, when you raise your right hand, the mirror image raises its left hand. This happens because the mirror reverses the front-back direction.

CloseWhen a driver looks in their rear-view mirror, the mirror creates a laterally inverted image. If AMBULANCE is written normally, it would appear reversed in the mirror. By writing it in reverse on the vehicle, the mirror shows it correctly, helping drivers identify it quickly.

CloseLateral inversion specifically refers to left-right reversal. For example, if you hold a book with the word TIME in front of a mirror, the mirror shows EMIT. The order of letters is reversed left to right.

CloseThe retina works like the film in a camera or the screen in a cinema. Light rays are focused by the cornea and lens onto the retina. The retina then converts the light into electrical signals for the brain.

CloseRods are very sensitive and work in low light, but they do not detect colour. Cones need bright light to work. In dim light, only rods are active, so we see shades of grey, not colours. In bright light, cones become active and we see colours.

CloseUsing the formula (360 / angle) − 1 = (360 / 90) − 1 = 4 − 1 = 3 images. If you stand between two mirrors at right angles, you will see three images of yourself.

CloseA kaleidoscope uses multiple reflections between plane mirrors arranged at an angle. The small coloured objects at one end are reflected many times, creating symmetrical patterns. Changing the position of the objects (by rotating the tube) changes the pattern.

CloseWhen white sunlight passes through a glass prism, it splits into a band of seven colours called a spectrum. This happens because different colours of light bend by different amounts when passing through the prism. This experiment was first done by Isaac Newton.

CloseThe iris is a circular muscle with pigment cells that give it colour. The amount and type of pigment determine whether eyes are blue, brown, green, or grey. The iris controls the size of the pupil.

CloseVitamin A is essential for good vision, especially for the functioning of rod cells in the retina. Foods rich in vitamin A include carrots, spinach, sweet potatoes, mangoes, and eggs. Deficiency of vitamin A can cause night blindness.

CloseFor a normal human eye, the most comfortable distance for reading is about 25 centimetre (10 inches). Holding a book too close strains the ciliary muscles that control the lens. Holding it too far makes the image small and hard to read.

CloseWatching TV in a dark room causes the pupil to become large, and the bright screen creates a high contrast. This can strain the eyes. It is better to have some soft background light in the room.

CloseBraille is read by moving the fingertips over the raised dots. The most commonly used finger is the index finger. People who are fluent in Braille can read at speeds comparable to sighted readers.

CloseThe sclera is the tough, white, protective outer layer of the eyeball. It is what we commonly call the white of the eye. It covers most of the eyeball, while the cornea is the transparent part at the front.

CloseThe aqueous humour is a clear, watery fluid that fills the front part of the eye between the cornea and the lens. It provides nutrients to the cornea and lens and helps maintain the shape of the front of the eye.

CloseThe vitreous humour is a clear, jelly-like substance that fills the space between the lens and the retina. It makes up about 80 percent of the eye’s volume and helps the eye maintain its round shape.

CloseLateral inversion causes the left and right sides of an object to swap in the mirror image. So your left ear is seen on the right side of the image, and your right ear is seen on the left side of the image.

CloseLateral inversion reverses the order of letters left to right. The letter L becomes L (but mirrored), E becomes E (but mirrored), F becomes F (but mirrored), T becomes T (but mirrored). The sequence becomes TFEL when read normally. This is why mirror writing looks strange.

CloseThe human retina has about 120 million rod cells. Rods are far more numerous than cones (which are about 6 million). This high number of rods makes the retina extremely sensitive to low light levels.

CloseCones are responsible for colour vision and for seeing fine details (high visual acuity). They are concentrated in a small area of the retina called the fovea. There are three types of cones sensitive to red, green, and blue light.

CloseColour blindness (difficulty distinguishing certain colours) is usually caused by the absence or malfunction of one or more types of cone cells. It is more common in males because the genes for cone pigments are on the X chromosome.

CloseMost kaleidoscopes use either two mirrors arranged in a V-shape (which gives a single repeating pattern) or three mirrors arranged in a triangle (which gives a full hexagonal pattern). Three mirrors are more common in high-quality kaleidoscopes.

CloseUsing the formula (360 / angle) − 1 = (360 / 45) − 1 = 8 − 1 = 7 images. As the angle between mirrors decreases, the number of images increases. At 30 degree, you get 11 images; at 10 degree, you get 35 images.

CloseThe eye lens is flexible. Ciliary muscles attached to the lens contract to make it thicker (for focusing on nearby objects) or relax to make it thinner (for focusing on distant objects). This ability is called accommodation.

CloseIn Braille, a machine called a Braille writer or a slate and stylus is used to create raised dots on thick paper. These dots are then read by touch. Modern technology also allows Braille to be displayed on refreshable Braille displays.

CloseLateral inversion is a property of all mirrors that produce a virtual image. Plane mirrors, convex mirrors, and concave mirrors (when the object is within the focal length) all produce laterally inverted images.

CloseThe best lighting for reading is to have light coming from behind you and falling onto the page. This illuminates the page well without shining directly into your eyes. Light shining into your eyes causes glare and strain.

CloseMultiple reflections are used in kaleidoscopes (to create patterns) and in periscopes (to see over obstacles). Both devices use two or more plane mirrors to reflect light multiple times.

CloseThe optic nerve must pass through the retina to reach the brain. At the point where it passes through, there is no space for rods or cones. This creates a small blind spot in each eye. Your brain fills in this gap using information from the other eye and from surrounding visual information.