focal point and focal length of concave mirror class 10

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This video is about focal point and focal length of concave and convex mirror class 10 physics chapter 12 geometrical optics.
Focal Point and Focal Length of Concave and Convex Mirrors

In reflection of light, spherical mirrors play an important role. A spherical mirror has a pole, principal axis, center of curvature, focal point, and focal length. Among these terms, the focal point and focal length are very important for understanding image formation by a concave mirror and a convex mirror.

The focal point of a mirror is defined as the point on the principal axis where rays of light parallel to the principal axis either meet or appear to meet after reflection. The distance between the pole of the mirror and the focal point is called the focal length. Thus, focal length is the distance from the pole to the focal point along the principal axis.

Focal Point and Focal Length of a Concave Mirror

A concave mirror is a spherical mirror whose reflecting surface is curved inward, like the inside of a spoon. When rays of light parallel to the principal axis strike a concave mirror, they reflect and actually converge at a point in front of the mirror. This point is called the real focal point of the concave mirror.

The focal point of a concave mirror lies in front of the mirror, on the same side as the incident light. Since the reflected rays actually meet at the focal point, the focal point of a concave mirror is called a real focal point. The focal length of a concave mirror is always taken as negative according to the sign convention used in physics.

The focal length of a concave mirror is equal to half of the radius of curvature, that is
f = R/2. A concave mirror is used in torches, headlights, solar cookers, and shaving mirrors because its focal point and focal length help in concentrating light.

Focal Point and Focal Length of a Convex Mirror

A convex mirror is a spherical mirror whose reflecting surface is curved outward. When rays of light parallel to the principal axis fall on a convex mirror, they reflect and diverge. These reflected rays do not actually meet, but they appear to come from a point behind the mirror. This point is called the virtual focal point of the convex mirror.

The focal point of a convex mirror lies behind the mirror. Since the rays only appear to meet, the focal point of a convex mirror is a virtual focal point. The focal length of a convex mirror is always taken as positive.

Just like a concave mirror, the focal length of a convex mirror is also equal to half the radius of curvature. Convex mirrors are commonly used as rear-view mirrors in vehicles because their focal length provides a wide field of view.

Conclusion

In summary, the focal point and focal length help us understand how a concave mirror converges light and how a convex mirror diverges light. The focal point, focal length, concave mirror, and convex mirror are essential concepts in Class 10 Physics and in the chapter Reflection of Light.


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