Why focal length of convex mirror and convex lens is positive while concave mirror and concave lens negative?

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Solution

This is due to its shape concave or convex.
By simply whether its concave or convex we can find whether its focal length is positive or negative. You must remember both concave & convex is cut from spherical mirror. From this we can find its focal length sign.

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Similar questions

A spherical mirror and a spherical lens each have a focal length of, -15 cm. The mirror and the lens are likely to be : (a) both concave. (b) both convex. (c) the mirror is concave but the lens is convex. (d) the mirror is convex but the lens is concave.

Q. According to New Cartesian Sign Convention:

(a) focal length of concave mirror is positive and that of convex mirror is negative
(b) focal length of both concave and convex mirrors is positive
(c) focal length of both concave and convex mirrors is negative
(d) focal length of concave mirror is negative and that of convex mirror is positive

What will happen to the focal length of a concave mirror, convex mirror, concave lens and convex lens when immersed in water? will it change ? if yes explain .

Question 7

You are provided with a convex mirror, a concave mirror, a convex lens and a concave lens. You can get an inverted image from

(a) both concave lens and convex lens.

(b) both concave mirror and convex mirror.

(d) Both convex mirror and concave lens.

Q. Question 4
A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be

(a) both concave
(b) both convex
(c) the mirror is concave and the lens is convex
(d) the mirror is convex, but the lens is concave

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Why focal length of convex mirror and convex lens is positive while concave mirror and concave lens negative?

This is due to its shape concave or convex. By simply whether its concave or convex we can find whether its focal length is positive or negative. You must remember both concave & convex is cut from spherical mirror. From this we can find its focal length sign.

This is due to its shape concave or convex.
By simply whether its concave or convex we can find whether its focal length is positive or negative. You must remember both concave & convex is cut from spherical mirror. From this we can find its focal length sign.