Question

a concave lens have a focal length of 10 cm.an object 2.5 cm high is placed 30 cm from the lens. determine the position and the size of the image ​

Answer 1

Answer:

Given that,

Distance u=−10cm

Height h=2.5cm

Radius of curvature R=30cm

We know that, −f= 2R

−f= 2

30

f=−15cm

Now, using mirror’s formula

f

1

=

v

1

+

u

1

−

15

1

=

v

1

−

10

1

v

1

=−

15

1

+

10

1

v=30cm

Now, the magnification is

m=

u

−v

m=

10

30

m=3

We know that,

m=

h

h

′

3=

2.5

h

′

h

′

=7.5cm

Hence, the size of the image is 7.5 cm