Question

An object of 3 cm size is placed at a distance of 20cm in front of a concave mirror of focal length of 15 cm. At what distance from the mirror a screen is to be placed to obtain a sharp image?

Answer 1

★ Answer:-

Ho = 3cm

U = -20 [sign convention]

F = -12. [sign convention]

V=?

Using Mirror formula,

1/f = 1/U+1/V

1/V=1/U-1/F

1/V=1/(-20)-1/(-12)

1/V = 1/(-20)+1/12

1/V = 1/20-1/12

1/V = 3-5/60

1/V=-2/60= -1/30

V = -30

We know that,

M = -V/U= Hi/Ho. [where Hi is height of

Image and Ho is height of object]

-V/U = Hi/Ho

-(-30)/(-20) = Hi/3

30/-20 = Hi/3 -20 Hi=30x3

Hi = 90/-20

Hi = 4.5

M is negative, So image is Inverted and

real.

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Answer 2

Answer:

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