Question

a convex lens of focal length 20cm is used and an object is placed at a distance of 50cm from the lens.if the object moves 20 cm towards the lens in 4 seconds what is the average velocity of the of the image

Answer 1

Explanation:

ANSWER

From lens equation

v

1

−

u

1

=

f

1

v

1

−

(−20)

1

=

(.3)

1

=

3

10

v

1

=

3

10

−

20

1

v

1

=

60

197

;v=

197

60

Velocity of image wrt. to lens is given by v

I/L

=m

2

v

O

/L

direction of velocity of image is same as that

of object

v

O/L

=5m/s

v

I/L

=(

197×20

60×1

)

2

(5)

1.16×10

−3

m/s towards the lens