## What is focal length of concave lens using convex lens?

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The focal length of the convex lens should be lesser than the concave lens. For u and v index correction should be applied. To obtain a real and inverted image, the needle should be kept at a certain distance. To avoid parallax, a distance of at least 30 cm should be maintained between the tip of the needle and eye.

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

Focal Length of Concave Mirror Formula

- 1f.
- 1f.
- Or 1f.
- Or f=uvu−v.
- F=R2.

**How do you find the focal length of a convex lens experiment?**

It can be found by obtaining a sharp image of the Sun or a distant tree on a screen, say a plane wall, or a sheet of paper placed on the other side of the lens and measuring the distance between the lens and the image with a scale. This distance is a rough estimate of the focal length, f of the convex lens.

### Why is the focal length of a concave lens negative?

Power of Lens: The ability of a lens to converge the light. As the concave lens diverge the light instead of converging so power is negative. so the focal length is reciprocal of it so it will also be negative.

### Is the focal length of a concave lens positive or negative?

negative focal length

A concave lens is a diverging lens, so it will always have a negative focal length. Therefore, the power of a concave lens is also negative.

**What is the focal length of concave and convex mirror?**

Focal length of a concave and convex mirror is half the radius of curvature of the mirror.

#### Why the focal length of concave lens is negative?

#### How will you distinguish a concave lens from a convex lens experimentally?

A concave lens is thinner in the middle and thicker at the edges. A convex lens is thicker in the middle and thinner at the edges….Watch the video to understand Concave and Convex mirrors.

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**What are the differences between the image formed by a convex lens and a concave lens?**

Generally, a convex lens forms a real image, but it can also create a virtual image when the object is in the middle of the focus and optical centre. On the contrary, the image formed by the concave lens is erect, virtual and smaller, than the object.

## Why focal length of concave lens is positive?

The focal length of a concave surface is negative, whereas the focal length of a convex surface is positive. Therefore, for a lens, the power of a concave and convex lens is negative and positive respectively. Whereas, for a mirror, the power of concave and convex lens is positive and negative respectively.

## Why the focal length of convex lens is positive and concave lens is negative?

Reason: Power of a concave lens is always less than the power of a convex lens, as power of concave lens is negative whereas power of convex lens is positive.

**How to find the focal length of a concave lens?**

To find the focal length of a concave lens using a convex lens. An optical bench with four upright (two fixed uprights in middle, two outer uprights with lateral movement), a convex lens (less focal length), a concave lens (more focal length), two lens holders, two optical needles (one thin, one thick), a knitting needle and a half metre scale.

### What is the difference between convex lens and concave lens?

The focal length of the convex lens should be lesser than the concave lens. For u and v index correction should be applied. To obtain a real and inverted image, the needle should be kept at a certain distance. To avoid parallax, a distance of at least 30 cm should be maintained between the tip of the needle and eye.

### How do you place a convex and concave lens?

The upright and convex lens should be placed at a distance from each other. The concave lens should be placed such that it coincides with the principal axes. Repeat steps 4 and 5. Repeat the experiment by moving the object needle towards the lens by 2cm. Repeat the experiment by moving the object needle away from the lens by 2cm.

**How to check the Col-linearity of a convex lens?**

Check the col-linearity of the tip of pin P1, optical center O of convex lens L1, and the tip of image pin P2 along a horizontal straight line which is parallel to the length of the optical bench. In this condition the planes of lens and both the pins would be perpendicular to the axis of the lens.