Question

class :10th chapte lights Reflection_Refraction ❣❣❣❣❣❣❣❣❣❣❣❣❣❣
✧༺♥༻✧✧༺♥༻✧
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Answer 1

focal length, f = +20 cm

Let the size of image be h

So,

size of object = 3h

We know,

Magnification, m = image size / object size

==> m = h/3h

==> m = 1/3

also,

m = - v / u

1/3 = -v / u

==> u = -3v ....(1)

We know,

==> 1/f = 1/v + 1/u

==> 1/20 = 1/v - 1/3v ( from (1) )

==> 1/20 = 3 - 1/3v

==> 3v = 40

==> v = 40/3

substituting value of v in (1)

==> u = -3v

==> u = -3 × 40/3

==> u = - 40 cm

Location of Object : 40 cm in front of the mirror

Type of Mirror : Convex mirror

Nature or Image : Virtual, Erect and smaller than the size of object.

Answer 2

Explanation:

focal length, f = +20 cm

Let the size of image be h

So,

size of object = 3h

We know,

Magnification, m = image size / object size

==> m = h/3h

==> m = 1/3

also,

m = - v / u

1/3 = -v / u

==> u = -3v ....(1)

We know,

==> 1/f = 1/v + 1/u

==> 1/20 = 1/v - 1/3v ( from (1) )

==> 1/20 = 3 - 1/3v

==> 3v = 40

==> v = 40/3

substituting value of v in (1)

==> u = -3v

==> u = -3 × 40/3

==> u = - 40 cm

Location of Object : 40 cm in front of the mirror

Type of Mirror : Convex mirror

Nature or Image : Virtual, Erect and smaller than the size of object.