Question

Focal length of a concave mirror is 15 cm. An object of length 5 cm is placed in front of this mirror. Draw neat diagrams to find the length and position of image when object is at 

(i) 5 cm, ii) 12 cm, (iii) 20 cm, (iv) 35 cm away from the mirror.

Answer 1

i) An object is kept at a distance of 5 cm from the mirror.

So the image is virtual ,erect and at a distance of 7.5 cm in the mirror.

Magnification = -(v/u) = -7.5/-5 = 1.5. So the image is 1.5 times the object .

ii)

∴ v = 60 cm

so the image is virtual and erect at a distance of 60 cm in the mirror.

Magnification = -(v/u) = -60/-12 = 5

∴ The image is enlarged by 5 times.

iii)

∴ v = -60 cm 

So the image is real and inverted and formed beyond c.

Magnification = -(v/u) = -(-60)/-20 = -3

so it is enlarged by three times.

iv)

∴  v = 105/4 = -26.25

The image is real and inverted and formed between F and C.

Magnification 

 

So the image is diminished.