By Team Aakash Byju's | 12th November 2022
The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. The distance between the lens and the image is 80 cm.
Experiment to Find the Focal Length of the Given Lens
v- Image distance
u - Object distance
Lens
V - Stand
Screen
Object
Image
(Question Continues)
If the image is three times the size of the flame, find the distance at which the candle is placed from the lens. Also, find the nature of the image formed and the nature of the lens.
Experiment to Find the Focal Length of the Given Lens
v- Image distance
u - Object distance
Lens
V - Stand
Screen
Object
Image
First, find the object distance (u), the distance between the candle and the lens using the formula.
Experiment to Find the Focal Length of the Given Lens
v- Image distance
u - Object distance
Lens
V - Stand
Screen
Object
Image
In the formula
m =
v
u
Where, m is the magnification (here m = 3) v is the image distance (here v = 80 cm) and u is the object distance
Object Size
Image Size
Lens
Since the image is formed on the other side of the lens, the magnification is taken as negative.
Candle
Lens
Screen
So, to find u
The distance between the candle and the lens must be 26.67 cm approximately.
=> -3 =
80
u
=> u=
-80
3
cm
To find the nature of the lens, check whether the focal length (f) is positive or negative, using the Lens formula.
1
=
v
1
f
1
u
-
By using formula
1
=
80
1
f
3
80
+
=>
f
=
20cm
=>
Since the focal length, f, is positive, the lens is a convex lens.