**Contents**show

## What is the power of lens if its focal length is 50 cm?

= 100/50 = **2 dioptre**.

## Is focal length of concave mirror positive?

The focal length f of a concave mirror **is positive**, since it is a converging mirror. Figure 2.

## Why is focal length positive for convex lens?

Convex lens **converges incident rays**. Hence the rays to converge at a point in front of the lens. So image distance is positive here. We can easily clarify that the focal length is positive direction for a Convex lens while negative with concave lens.

## Is the power of concave lens positive?

The power of the **concave lens is negative**. Concave lens surfaces have a virtual radius of curvature, and thus a negative curvature. Optical power is denoted by the same convention signs that are used for focal length.

## What is the focal length of concave mirror?

Focal Length – **The distance between the pole P of the concave mirror and the focus F** is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a ‘Real image’ of a distant object at its focus, as shown in the figure.

## Is the power of a lens is 2D what is its focal length?

Power of a lens is -2D, negative sign indicates it is a Concave lens. Focal length (in meters)=1/power of the lens, thus focal length=1/2=0.5m=50cm. Answer: Since, **Power P = -2 D**, Focal length f = 100/(-2) = – 50 cm.

## How we can find focal length?

The focal length of a double convex lens is given by the formula **(1/v) + (1/u) = (1/f)**, where u is the distance between the object and the lens, v is the distance between the image and the lens.

## What is the value of rough focal length of convex lens?

Answer: 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.

## What is the focal length if power is?

The power of a lens is defined as **the reciprocal of the focal length**. Lens power is measured in dioptres (D). Converging (convex ) lenses have positive focal lengths, so they also have positive power values. Diverging (concave ) lenses have negative focal lengths, so they also have negative power values.