concave and convex mirrors
- The reflecting surface of a convex mirror bulges out at the centre.
- The reflecting surface of a concave mirror 'caves in' at the centre.
terms used to describe spherical mirrors
- The centre of the spherical mirror is called the pole of the mirror. (P)
- The centre of the sphere from which the mirror is made is called the centre of curvature of the mirror. (C)
- The straight line joining the pole to the centre of curvature is called the principal axis or axis of the mirror.
- The point half way between the centre of curvature and the pole is called the focus or focal point of the mirror. (F)
- The distance from the focus to the pole is called the focal length of the mirror. (f)
REFLECTION OF LIGHT FROM A CONCAVE MIRROR
how an image is formed in a concave mirror
A real image is an image formed by the actual intersection of rays. Such an image can be located on a screen or by the method of no parallax.
FOR A CONCAVE MIRROR:
FOR A CONCAVE MIRROR:
- If the object is outside the focus the image is real and located in front of the mirror.
- If the object is inside or at the focus the image is virtual and is located behind the mirror.
A virtual image is an image formed by the apparent intersection of rays. Such an image can never be formed on a screen. It can be located by the method of no parallax.
uses of concave mirrors
- Dentist's mirrors: by placing a mirror close to teeth, they are positioned inside the focal length, and a magnified image is formed.
- Shaving or make-up mirrors: These are often found in bathrooms. If you stand close to them, you get an enlarged image of your face.
formula for focal length
- For virtual images, v is always negative.
- For a convex mirror, f is always negative.
formula for magnification
reflection of light from a convex mirror
the formation of an image by a convex mirror
FOR A CONVEX MIRROR:
- The image is always virtual and located behind the mirror.
- The image is always diminished. The nearer the object is to the mirror the bigger the image.
uses of convex mirrors
- In shops as security devices, so that a large can be easily seen.
- On country roads, to aid vision on dangerous corners.
- As the wing mirrors in a car, giving a large field of vision (but with the problem that the image is diminished and can lead a driver to feel another car is further away than it really is.)