A concave mirror has focal length of 20 cm. At what distance from the mirror 5 cm tall object be placed so that it forms an image at 15 cm from the mirror.Also calculate the size of the object.
Answers
Answered by
3
Given: A concave mirror of radius of curvature 20cm forms image of the sun. The diameter of the sun subtends an angle 1
o
on the earth.
To find the diameter of the image
Solution:
As sun is more far from the earth,
Then we take u = infinite
Radius of curvature, R=−20cm
Focal length, f=
2
R
=
2
−20
=−10cm
From the mirror formula
v
1
+
u
1
=
f
1
⟹
(−10)
1
=
v
1
+
∞
1
⟹v=−10cm
And we also know that
Angle = 1
o
=
180
∘
π
We know,
θ=
f
d
, where θ is the angle subtended on the earth, d is the diameter of the image and f is the focal length of the concave mirror.
d=θ×f
⟹d=
180
∘
π
×10
⟹d=
18
π
cm
is the diameter of the image
hope it helps u☺❤❤
Similar questions