1.A 6.0 cm tall object is placed 20 cm in front of a convex mirror with focal -1
ID: 1454247 • Letter: 1
Question
1.A 6.0 cm tall object is placed 20 cm in front of a convex mirror with focal -100 cm focal length. Which of the following describes the image?
real and inverted
real and upright
virtual and inverted
not possible to determine
2.A coin has been dropped inadvertently into a bucket full of cleaning fluid (n=1.13). The bottom of the bucket is 15cm beneath the top – how far beneath the surface does the washer therefore APPEAR to be?
13.3cm
17.0cm
7.5cm
More information is needed
3.A concave mirror has an object placed 40 cm in front of it. An image forms 60 cm in front of the mirror. What is the focal length of the mirror?
60 cm
120 cm
-120 cm
100 cm
24 cm
not possible to determine
Explanation / Answer
1) The image is virtual and upright
given
u = 20 cm
f = -100 cm
let v is the image distance.
1/u + 1/v = 1/f
1/v = 1/f - 1/u
1/v = 1/(-100) - 1/20
v = -16.7 cm
2) 13.3 cm
apparent depth = real depth/n
= 15 cm/1.13
= 13.3 cm
3) 24 cm
given
u = 40 cm
v = 60 cm
apply, 1/f = 1/u + 1/v
1/f = 1/40 + 1/60
f = 24 cm
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