Radius of curvature of concave mirror is 40 cm and the size of real im...
Given:
- Radius of curvature of concave mirror = -40 cm (negative sign indicates concave mirror)
- Size of real image = 2 × size of object
To find: Object distance
Solution:
- Step 1: Use the mirror formula to find the image distance
The mirror formula is given by:
1/f = 1/v - 1/u
where,
- f = focal length of the mirror
- v = image distance
- u = object distance
As the given mirror is concave, the focal length is negative. Therefore, f = -40 cm.
Substituting the values in the mirror formula, we get:
1/-40 = 1/v - 1/u
Simplifying the equation, we get:
(v - u)/uv = -1/40
v - u = -uv/40
40v - 40u = -u(v)
40v = u(v-40)
v = 2u
Therefore, the image distance is twice the object distance.
- Step 2: Use the magnification formula to find the magnification of the mirror
The magnification formula is given by:
m = -v/u
Substituting the value of v, we get:
m = -2
Therefore, the magnification of the mirror is -2, which means the image is inverted and twice the size of the object.
- Step 3: Use the magnification formula again to find the object distance
Substituting the value of magnification and image distance in the magnification formula, we get:
m = -v/u
-2 = -2u/u
-2 = -2
Therefore, the object distance is u = 40 cm.
Answer: The object distance is 40 cm.