Question

An object placed 15 cm in front of a lens forms a real image three times magnified. where is the image formed
1. 45 cm
2. 20 cm
3. 50 cm
4. 5.5 cm​

Answer 1

Answer:

According to new cartesian sign convention,

Object distance, u=−15 cm

Focal length of the concave mirror, f=−10 cm

Height of the object, h

0

=2 cm

According to mirror formula,

v

1

+

u

1

=

f

1

⇒

v

1

=

f

1

−

u

1

=

−10

1

−

1−5

1

=

−10

1

+

15

1

or v=−30 cm

The image is formed at a distance of 30 cm from the mirror on the same side of the object.

It is a real image.

Magnification of the mirror, m=

u

−v

=

h

0

h

1

⇒

−15

−(−30)

=

2

h

1

⇒h

I

=−4 cm.

Negative sign shows that image is inverted.

The image is real, inverted, of size 4 cm at a distance of 30 cm in front of the mirror.