Why is the image of an object magnified when we see it using a magnifying glass? The mirror used in a magnifying glass differs from our daily use of mirrors. Certain laws on the movement of light help us understand the formation of images by spherical mirrors. Ray Optics has answers to your questions on the working of spherical mirrors.
What are Spherical Mirrors?
A spherical mirror is a mirror that has a curved reflective surface that forms a part of a sphere. It can be either concave or convex in design. The mirror’s surface curve provides optical characteristics which enable it to reflect and tweak light.
There are two kinds of spherical mirrors:
Concave Spherical Mirror
A mirror with an inwardly curving surface resembling a sphere’s interior is called a concave spherical mirror. On the concave side, it is coated with reflective material.
Whenever parallel light rays contact a concave mirror, they converge and join at the focal point.
Concave mirrors are often used in tools like reflecting telescopes, cosmetic mirrors, and automobile headlights.
Convex Spherical Mirror
A mirror with an outward-curving surface resembling a sphere’s exterior is called a convex spherical mirror. On the convex side, it is coated with reflective material.
A convex mirror causes parallel light beams to diverge as though they had emerged from the focal point.
Convex mirrors are often used in rear-view mirrors, surveillance mirrors, and magnifying glasses because they have a broader field of view.
Alt text: Concave and convex mirror
Terminologies of Spherical Mirror
Alt text: Components of spherical mirrors
To understand the working of spherical mirrors, we need to understand certain terminologies of a spherical mirror, such as the following:
- Pole (P): The pole represents the geometric centre of the mirror surface. It is the point where the mirror stays attached or the area where it is symmetrically bent around.
- Centre of Curvature (C): The centre of curvature is the central point of the sphere, of which the mirror is a part. A convex mirror has its centre of curvature behind it, whereas a concave mirror has it in front of it.
- Principal Axis: The principal axis is the imaginary line that runs through the pole and the mirror’s centre of curvature. It is parallel to the surface of the mirror.
- Focal Point (F): The focal point is the principal axis point where the parallel incident rays following reflection or refraction converge or seem to converge. The focal point of a convex mirror is behind the mirror, as compared to a concave mirror, where it is in front of the mirror.
- Focal length (f): The focal length is the distance between the mirror’s pole and the focal point. It determines the mirror’s optical characteristics and is represented by the letter “f.” Convex mirrors have a negative focal length, while concave mirrors have a positive focal length.
- Aperture: The effective diameter of the mirror is referred to as the aperture. It refers to the size of the reflective surface.
- Radius of Curvature (r): The radius of curvature is the radius of the sphere of which the mirror is a part. It is the distance that exists between the mirror’s pole and its centre of curvature.
Conclusion
This article must have given you a short answer to your questions regarding the working of spherical mirrors. The ray optics of spherical mirrors and plane mirrors are quite different; the bending of light, the size of the image, etc., are different in both mirrors. Spherical mirrors are used in several daily activities. The curvature of these mirrors is what makes the difference in the images.
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