Question

(ii) A student conducts an experiment using a concave mirror with focal length of
30cm. He places an object at a distance of 20cm in front of the mirror. Where is the
image likely to form?
(a) 10cm in front of the mirror
(c) 30 cm behind the mirror
(b). 20 cm in front of the
mirror
(d) 60 сm behind the mirror

Answer 1

Explanation:

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so here we go

now here concave mirror ,,

focal length (f)=-30 cm

object distance (u)=20 cm

so we have to image distance ie v

so apply mirror formula ie

1/v+1/u=1/f

so substitute given values we get

1/v=1/20=1/(-30)

now be careful as there is negative sign

so 1/v=1/(-30)-1/20

=1/30+1/20

=(30+20)/30×20

=50/600

thus 1/v=1/12

hence v=12

hence the image is formed above principal axis and lies to the ryt of it ie in quadrant 1

hence image is likely to form 12 cm infronnt of the mirror

Answer 2

Answer:

1/f= 1/u + 1/v ( without sign convensation)

F= focal length

U= object distance

V= image distance

Power= 1/f ( in meters)

1/f = 1/60 +1/30

=. 1/60+ 2/60

1/f = 3/60

F= 60/3 = 20 cm

Power= 1/f = 1/ 0.2

= 0.05 Diopters

Power= + 0.05 D

(Convex lenses have positive power values. Concave lenses have negative power values)

Explanation:

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