9. For a plane mirror, what is ratio of the object height y to the image height

Question

9.

For a plane mirror, what is ratio of the object height y to the image height y?

1/2

0

1

2

10.

For a plane mirror, how is the object distance s related to the image distance s?

s = 2s

s = -s

s = s/2

s = s

11.

An object is placed 15.0 cm to the left of a thin convex lens of focal length 20.0 cm. The image of this object is located

8.57 cm to the right of the lens.

60.0 cm to the left of the lens.

30.0 cm to the left of the lens.

60.0 cm to the right of the lens.

8.57 cm to the left of the lens.

9.

For a plane mirror, what is ratio of the object height y to the image height y?

1/2

0

1

2

10.

For a plane mirror, how is the object distance s related to the image distance s?

s = 2s

s = -s

s = s/2

s = s

Explanation / Answer

9)Answer : The ratio is 1.

10) Answer : s = -s'

Explanation for both 9 and 10 is below:

We know that, the focal length of plane mirroe is infinity.Let f be the focal length, s be the object distance and s' be that of image.

from lens eqn we know that : 1/f = 1/s + 1/s' when f = infinity

1/s + 1/s' => s = -s'

s = s' Problem 10 Proved here.

We know that,

M = -s'/s = h'/h

-(-s)/s = h'/h

h'/h = 1 Problem 9 proved here.

11) Hence, i = -60 cm, to the left of the lens.

explanation:

Given that,

object distance = o = 15 cm

focal length = f = 20 cm (positive for convex lens)

Let i be the image distance,

We know from lens eqn: 1/f = 1/i + 1/o

i = o x f / ( o - f ) = 15 x 20 ( 15 - 20) = -60 cm

Hence, i = -60 cm, to the left of the lens.

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