# Question: Can we find rough focal length for concave lens and why?

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The distance of the screen from the lens gives us the rough focal length of the lens. This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it can be taken on a screen.

## Can you find the rough focal length of concave lens?

18. Can you find rough focal length of a concave lens? Answer. No, because it does not form a real image to be obtained on a screen.

## Can we find the rough focal length of a concave mirror?

Arrange your mirror, meter stick, and screen. Point the mirror at distant (greater than 10 m) object and move the screen along the meter stick until you obtain a sharp image of the distant object on the screen. The distance between the mirror and the screen is the approximate focal length of the mirror.

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## How do you find the focal length of a concave lens?

You can calculate the focal length (F) of combination of lenses using the formula F = uv/(u+v). The focal length of convex lens (f1) is shown inside the simulator window. You can calculate the focal length of the concave lens using the formula f2 = (f1F/(f1-F).

## Can we find rough focal length of convex mirror?

No, we cannot find rough focal length of a convex mirror, as it forms only a virtual image, which cannot be taken on a screen.

## Why do you find rough focal length in convex lens practical?

The rough focal length of a convex lens is obtained by forming sharp image of a very distant object on a screen. The distance of the screen from the lens gives us the rough focal length of the lens.

## Why do we use rough focal length?

Answer: The rough focal length of convex lens is obtained by forming the sharp image of very distant object on screen. Explanation: The focal length of a concave mirror can be found using these method we can put an object far away from the concave mirror and place a screen to obtain the image formed.

## How do you find focal length of a concave mirror?

Focal Length of Concave Mirror Formula

The focal length of the convex mirror is positive, whereas that of the concave mirror is negative. The same can also be proved by using the mirror formula: (1/f = 1/v +1/u).

## How do you find the focal point of a concave mirror?

Explanation:

1. f:focal point.
2. R:the center of curvature.
3. i:distance between image and vertex(mirror’s center)
4. o: distance between object and vertex.
5. f=R2.
6. or.
7. 1f=1o+1i.
8. 1f=i+oi⋅o.
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## Why a concave lens is used to determine the focal length of a convex lens?

The Theory:

So the light beams passing through the lens are spread out or diverged. Therefore, the concave lens is called a diverging lens. The image formed by a concave lens is virtual and diminished. Since a concave lens will not produce a real image, a convex lens is used to measure its focal length.

## Why we Cannot find the focal length of convex mirror and concave lens without combining it with convex lens experimentally?

Answer. No, we cannot find the rough focal length of convex mirror. It is so because the image formed by a convex mirror is always virtual and cannot be obtained on a screen.

## Can you measure rough focal length of a convex lens?

The rough focal length of a convex lens is obtained by forming sharp image of a very distant object on a screen. … This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it can be taken on a screen.

## Can you determine the rough focal length of a convex mirror by forming image of a distant object with its use?

No, the rough focal length for a convex mirror cannot be found out because it always forms a virtual image for any position of the object.