Question

If a man face is 25cm in front of concave shaving mirror producing erect image 1.5 times the size of face, focal length of the mirror would be :​

Answer 1

Answer:

f=-75cm

Explanation:

By magnification formula:

m=-v/u

1.5=-v/-25

-v=1.5*-25

-v=-37.5

v=37.5

By mirror formula:

1/f=1/v+1/u

1/f=1/37.5+-1/25

lcm=75

1/f=2/75+-3/75

1/f=-1/75

f=75/-1

f=-75cm

Hope you understands....

Answer 2

Given,

Distance of face from mirror=25cm

Erect image is formed which is 1.5 times the size of the face.

To Find,

Focal length of the mirror.

Solution,

Face is 25cm in front of the mirror

So, u=-25cm

Magnification of the mirror=1.5

We know the magnification formula,

m=-v/u

⇒1.5=-v/-25

⇒-v=1.5*-25

⇒-v=-37.5

⇒v=37.5

By using mirror formula to find the focal length of the mirror,

1/f=1/v+1/u

⇒1/f=1/37.5+-1/25

⇒1/f=2/75+-3/75

⇒1/f=-1/75

⇒f=-75cm

Hence, focal length of the mirror is 75cm.