What is an Image?
An image is formed when light from an object reaches our eyes.
The image represents the appearance of the object as perceived by the observer.
Images can be formed by mirrors and lenses, which use light in different ways.
Mirrors form images by reflection of light, while lenses form images due to refraction of light.
Depending on how light behaves, an image may appear upright or inverted, larger or smaller, and at different positions relative to the object.
Understanding how images are formed is central to the study of optics. In this topic, we will explore how mirrors and lenses use light to form images and how these images help us see and understand the world around us.
What is a Mirror?
A mirror is a smooth, polished surface that reflects most of the light falling on it. When light from an object strikes a mirror, it is reflected back into the same medium, allowing an image to be formed.
Mirrors do not produce light on their own. They simply redirect light by reflection, enabling us to see images of objects placed in front of them. Mirrors are among the simplest and most widely used optical devices in everyday life.
Types of Mirrors
Mirrors are classified based on the shape of their reflecting surface.
Plane Mirror
A plane mirror has a flat reflecting surface. The image formed by a plane mirror is upright, of the same size as the object, and appears to be located behind the mirror.
Plane mirrors are commonly used in homes, vehicles, and optical instruments.
Concave Mirror
A concave mirror has a reflecting surface that curves inward. It can form different types of images depending on the position of the object.
Concave mirrors are used in applications such as shaving mirrors, headlights, and reflecting telescopes.
Convex Mirror
A convex mirror has a reflecting surface that curves outward. It always forms an upright, diminished image.
Convex mirrors are commonly used as security and rear-view mirrors because they provide a wider field of view.
Image Formation with Mirror
Image formation by mirrors occurs due to the reflection of light. The characteristics of the image—such as size, orientation, and position—depend on the type of mirror and the position of the object.
The formation of images by mirrors is commonly explained using ray diagrams, which show the paths taken by light rays after reflection. These diagrams help us predict how and where images will be formed.
What is a Lens?
A lens is a transparent optical device made of glass or plastic that bends light passing through it. Unlike mirrors, lenses form images by refraction of light.
Lenses are designed to converge or diverge light rays, allowing them to form images at different positions. Lenses play a vital role in vision and in many optical instruments.
Types of Lenses
Lenses are classified based on their shape and how they affect light.
Convex Lens
A convex lens is thicker at the centre than at the edges. It converges parallel light rays to a point.
Convex lenses are used in magnifying glasses, cameras, microscopes, and the human eye.
Concave Lens
A concave lens is thinner at the centre and thicker at the edges. It diverges light rays.
Concave lenses are commonly used in spectacles to correct short-sightedness.
Image Formation with Lens
Image formation by lenses occurs due to the refraction of light as it passes through the lens. The nature of the image depends on the type of lens and the position of the object relative to the lens.
Ray diagrams are used to understand how lenses bend light and where images are formed. These diagrams help determine whether an image is real or virtual, upright or inverted, and magnified or diminished.
Glossary of Key Terms
Recap of the Key Terms in Mirrors & Lenses
Concave Lens: A lens that is thinner at the centre and thicker at the edges. It diverges light rays and always forms a virtual, upright, and diminished image.
Concave Mirror: A spherical mirror with a reflecting surface that curves inward. It can form real or virtual images depending on the object’s position.
Convex Lens: A lens that is thicker at the centre than at the edges. It converges parallel light rays and can form real or virtual images.
Convex Mirror: A spherical mirror with a reflecting surface that curves outward. It always forms a virtual, upright, and diminished image.
Image: The optical representation of an object formed when light rays reflected or refracted from the object reach the observer’s eyes.
Lens: A transparent optical device made of glass or plastic that forms images by bending light through refraction.
Mirror: A smooth, polished surface that reflects light and forms images by the process of reflection.
Optics: The branch of physics that deals with the study of light, its behaviour, and the formation of images using mirrors and lenses.
Plane Mirror: A mirror with a flat reflecting surface that forms an upright image of the same size as the object, appearing behind the mirror.
Ray Diagram: A graphical representation used to trace the path of light rays and predict the position, size, and nature of images formed by mirrors or lenses.
Real Image: An image formed when light rays actually meet after reflection or refraction. It can be projected on a screen.
Reflection: The bouncing back of light into the same medium when it strikes a smooth surface such as a mirror.
Refraction: The bending of light when it passes from one medium to another due to a change in its speed.
Virtual Image: An image formed when light rays appear to meet but do not actually converge. It cannot be projected on a screen.
Quiz
Recap the concepts you have learnt. Try to answer the questions. You can find the answer to any question by clicking on the icon.
What is reflection of light?
Reflection is the bouncing back of light from a surface.
What is a mirror?
A mirror is a surface that reflects light to form images.
What is a plane mirror?
A flat mirror that produces upright images of the same size.
What is a concave mirror?
A mirror with a reflecting surface that curves inward.
What is a convex mirror?
A mirror with a reflecting surface that bulges outward.
What is refraction?
Refraction is the bending of light when it passes from one medium to another.
What is a lens?
A transparent optical device that refracts light to form images.
What is a convex lens?
A lens that converges light rays to a focus.
What is a concave lens?
A lens that diverges light rays.
What is focal length?
The distance between the lens or mirror and its focus.