Question

the image formed by a convex mirror is 1 / 3rd of the object. If the focal length of the mirror is 12 cm, where is the object and where the image.
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Answer 1

ANSWER:

• image is at a distance of 8 cm right of the convex mirror

• object is at a distance of 24 cm left of the convex mirror.

FORMULAE USED:

• magnification , m = -v / u

• magnification, m = height of image / height of object

• mirror formula: 1/f = 1/v + 1/u

KEYS:

• f is the focal length of the convex mirror.

• u is the object distance

• v is the image distance

• m is the magnification

• $h_o$ is the height of object

• $h_I$ is the height of image

SOLUTION:

refer to the three attachments

SIGN CONVENTION:

• the points to the left of mirror is negative.

• the points to right of mirror is positive

• the points above the principal axis is positive.

• the points below the axis is negative.

NOTES:

• negative sign in object distance indicates that the object is left to the convex mirror.

• positive sign in image distance indicates that it is present right to the mirror.

• convex mirror usually have positive focal length

• for concave mirror , the focal length is negative.

FOR LENS:

• convex lens has positive fecal length and concave lens has negative focal length

• lens formula, 1/f = 1/v - 1/u

• magnification ,m = v/u