Light

CloseThe first law of reflection says that the angle of incidence is always equal to the angle of reflection. Both angles are measured from the normal, which is an imaginary line perpendicular to the reflecting surface at the point where the light ray strikes.

CloseThe second law of reflection says that the incident ray, the reflected ray, and the normal all lie in one flat plane. This means if you draw them on paper, they will not go in different directions out of the paper.

CloseThe angle of incidence is defined as the angle between the incident ray (the incoming light ray) and the normal. The normal is an imaginary line drawn perpendicular to the reflecting surface at the point of incidence.

CloseThe angle of reflection is the angle between the reflected ray (the outgoing light ray) and the normal. Just like the angle of incidence, it is measured from the normal, not from the surface.

CloseAccording to the first law of reflection, the angle of incidence equals the angle of reflection. So if the angle of incidence is 30 degree, the angle of reflection is also 30 degree.

CloseThe normal is an imaginary line drawn at the point where the light ray hits the surface. It stands straight up from the surface at a right angle (90 degree). The word normal in geometry means perpendicular.

CloseRefraction is the bending of light when it travels from one transparent medium to another, such as from air to water or from air to glass. This happens because light changes speed when it enters a different medium.

CloseThe incident ray is the light that strikes the surface. The reflected ray is the light that bounces off the surface. The refracted ray is the one that passes into another medium and bends.

CloseIncident means falling on. The incident ray is the incoming light ray that approaches the surface. After striking the surface, it may be reflected, refracted, or absorbed.

CloseRegular reflection (also called specular reflection) occurs when light rays hit a smooth, shiny surface. All parallel incident rays remain parallel after reflection, forming a clear image. A plane mirror gives regular reflection.

CloseDiffuse reflection occurs when light hits a rough or uneven surface. The parallel incident rays get scattered in different directions because the surface has many tiny surfaces at different angles. This is why we can see a book or a wall from any direction.

CloseThe blind spot is a small area on the retina where the optic nerve passes through to send signals to the brain. There are no rod cells or cone cells at this spot, so no image is formed there.

CloseWhen reflected light from one mirror strikes another mirror and gets reflected again, it is called multiple reflection. This principle is used in periscopes and kaleidoscopes. Each reflection follows the laws of reflection.

CloseA periscope uses two plane mirrors placed at 45 degree angles inside a tube. Light from an object enters the top, reflects off the first mirror, travels down the tube, reflects off the second mirror, and enters the eye. This allows viewing over obstacles.

CloseA kaleidoscope contains two or more plane mirrors arranged in a tube. Small coloured objects at one end get reflected many times between the mirrors, creating beautiful symmetrical patterns due to multiple reflections.

CloseThe angle of incidence is measured from the normal, not from the mirror surface. The normal is perpendicular to the mirror. If the incident ray makes 40 degree with the mirror, then it makes 90 − 40 = 50 degree with the normal. So angle of incidence = 50 degree.

CloseWhen a ray falls normally (straight on) to a mirror, it travels along the normal. The angle between the incident ray and the normal is zero. So the angle of incidence is 0 degree. The reflected ray goes back along the same path.

CloseSince the angle of incidence is 0 degree, the first law of reflection tells us that the angle of reflection must also be 0 degree. The reflected ray goes straight back along the normal, exactly opposite to the incident ray.

CloseA plane mirror always forms a virtual image (cannot be caught on a screen) that is upright (same orientation as the object) and laterally inverted (left and right are swapped). The image appears to be behind the mirror.

CloseBy definition, the normal is an imaginary line drawn perpendicular (at 90 degree) to the surface at the exact point where the incident ray strikes. It is used as a reference to measure angles of incidence and reflection.

CloseDiffuse reflection happens on rough, uneven surfaces. The rough plaster wall has many tiny bumps and hollows. Light rays hit these different tiny surfaces and scatter in many directions, so no clear image is formed.

CloseA calm lake has a smooth, flat water surface. It acts like a mirror and gives regular reflection (specular reflection). You can see the reflection of trees or clouds in it. Newspaper, cloth, and tree bark are rough and give diffuse reflection.

CloseLight travels at different speeds in different transparent materials. When light enters from one medium to another (e.g., air to glass), its speed changes. This change in speed causes the light ray to bend at the boundary. That bending is refraction.

CloseLight rays coming from the part of the pencil under water travel from water to air. They bend at the surface because of refraction. Our brain assumes light travels in straight lines, so the underwater part appears at a different position, making the pencil look bent.

CloseAngle of incidence = 25 degree. Angle of reflection = 25 degree. The angle between the reflected ray and the normal is 25 degree. Since the normal is perpendicular to the mirror, the angle between the reflected ray and the mirror = 90 − 25 = 65 degree.

CloseAngle of incidence = 45 degree, so angle of reflection = 45 degree. The angle between the incident ray and the reflected ray is the sum of these two angles (on opposite sides of the normal). So 45 + 45 = 90 degree.

CloseThe pages of a book have a rough surface. When light falls on them, diffuse reflection sends light in many directions. Some of this scattered light enters your eyes no matter where you sit. If the book gave regular reflection like a mirror, you would see it only from one specific angle.

CloseThe blind spot is the region where the optic nerve exits the retina. There are no light-sensitive rod cells (for dim light) or cone cells (for colour) at this spot. Therefore, no image is detected there. Your brain fills in the missing information from the surrounding area.

CloseThe normal is a construction line used in ray diagrams. It must pass exactly through the point where the light ray hits the surface, and it must be at a right angle (90 degree) to the surface at that point.

CloseWhen two mirrors face each other or are placed at an angle, light bounces back and forth between them many times. Each bounce creates a new image. The number of images depends on the angle between the mirrors. This is an application of reflected light being reflected again.

CloseThe second law of reflection states that all three — the incident ray, the reflected ray, and the normal — are in the same plane. This means you can draw them on a single flat sheet of paper. The first law is about equality of angles.

CloseBy definition, the angle of incidence is the angle between the incident ray and the normal. It is never measured from the mirror surface. Similarly, the angle of reflection is measured from the normal.

CloseEven on a rough surface, each tiny flat area follows the laws of reflection. However, because the tiny surfaces face different directions, the reflected rays go in many different directions. So the laws still hold locally, but the overall effect is scattering.

CloseFor a plane mirror, the image appears as far behind the mirror as the object is in front. If you stand 1 metre in front of a mirror, your image looks 1 metre behind the mirror. The total distance between you and your image is 2 metre.

CloseA simple periscope uses two plane mirrors. One mirror is placed at the top of the tube at 45 degree, and another at the bottom at 45 degree. Light reflects from the top mirror to the bottom mirror and then to the eye. This allows seeing over walls or from inside a submarine.

CloseReflected light behaves just like any other light. When it strikes a second mirror, it obeys the same laws of reflection. The angle of incidence on the second mirror equals the angle of reflection from that mirror. This is how multiple reflections work.

CloseWhen light enters glass from air, it slows down and bends towards the normal. When it leaves glass back into air, it speeds up and bends away from the normal. This bending is refraction. A glass lens works on this principle.

CloseThe blind spot has no rods or cones. Even if light falls on that part of the retina, it cannot be converted into electrical signals for the brain. You normally do not notice your blind spot because your brain fills in the gap using information from the other eye and surrounding areas.

CloseLateral inversion means that the left side of the object appears as the right side in the image, and vice versa. For example, when you raise your left hand, the mirror image raises its right hand. This happens because the mirror reverses the front-back direction.

CloseIf the ray makes 20 degree with the mirror surface, then the angle with the normal is 90 − 20 = 70 degree. So angle of incidence = 70 degree. By the law of reflection, angle of reflection is also 70 degree.

CloseA virtual image is one that cannot be projected onto a screen. The light rays do not actually come from the image position; they only appear to come from there. The image in a plane mirror is behind the mirror, so no screen can catch it.

CloseOn a rough surface, each tiny facet faces a different direction. Even though each ray obeys the law of reflection, the reflected rays go off in many different directions. They are no longer parallel to each other. This is why rough surfaces do not form clear images.

CloseThe point of incidence is the exact spot on the reflecting surface where the incident ray hits. The normal is drawn at this point. All angles and rays are defined with respect to this point.

CloseThe image is formed 50 cm behind the mirror. So the object is 50 cm in front, and the image is 50 cm behind. The total distance from object to image is 50 + 50 = 100 cm.

CloseLight does not lose its ability to reflect after one bounce. It can reflect many times. Each reflection follows the laws of reflection. Periscopes, kaleidoscopes, and multiple mirror systems work because reflected light can be reflected again and again.

CloseMost everyday objects (clothes, paper, wood, walls) have rough surfaces. They scatter light in all directions due to diffuse reflection. This is why we can see them from any angle. If they gave only regular reflection, we would see them only from specific positions.

CloseThe blind spot is a small area on the retina, which is the light-sensitive layer at the back of the eye. The optic nerve leaves the eye at this point, creating a gap in the layer of photoreceptor cells.

CloseAngle of incidence = 60 degree, so angle of reflection = 60 degree. The reflected ray makes an angle of 60 degree with the normal. Since the normal is perpendicular to the mirror, the reflected ray makes an angle of 90 − 60 = 30 degree with the mirror surface.

CloseWhen light enters water from air, it slows down because water is optically denser than air. Its frequency remains the same, but its wavelength decreases. The change in speed causes the ray to bend (refract). The colour does not change unless the light is dispersed.

CloseThe laws of reflection apply to all reflecting surfaces, whether flat (plane) or curved (concave or convex). For curved mirrors, the normal is taken at the point of incidence, and the same two laws apply. This is why we can draw ray diagrams for curved mirrors using these laws.