I have found the formula for the effective focal length f of two thin lenses with focal lengths f1 and f2 separated by distance d to be 1f=1f1+1f2−df1f2.

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## How do you find the focal length of a lens from its radius?

Focal Length of a Curved Mirror A mirror with a curvature radius R of the surface has a focal length f = R / 2, if the beam axis is normal to the mirror surface.

## How do you find the distance between objects on a lens?

Once the focal length is calculated, mark point F on both the sides of the lens. Mark a point 2F, as the distance between the lens is double the focal length of the lens. Place the candle at a distance beyond 2F and adjust the height of the centre of the lens with the height of the flame.

## How do you find the image distance of a concave lens?

## What is the focal length of two convex lenses?

The focal length of the combination of two convex lenses in contact is f. and if they are separated by a distance, then focal length of the combination is f1. .

## How do you find total focal length?

1/Focal length = 1/Image distance + 1/Object distance , where: Image distance and Object distance are given in mm.

## What is the focal length of the lens?

The focal length of a lens is determined when the lens is focused at infinity. Lens focal length tells us the angle of view—how much of the scene will be captured—and the magnification—how large individual elements will be. The longer the focal length, the narrower the angle of view and the higher the magnification.

## How do you find the focal length of a lens with refractive index?

Step 1: Identify the index of refraction, n , outer radius R1 , and inner radius R2 . Step 2: Substitute the values from step 1 into the lensmaker equation, 1f=(n−1)(1R1−1R2) 1 f = ( n − 1 ) ( 1 R 1 − 1 R 2 ) . Step 3: Solve for the focal length, f .

## How do you calculate the focal length of a convex lens?

- The focal length of a convex lens is the distance between the center of a lens and its focus.
- The focal length of convex lens formula is object distance multiplied by the image distance divided by the difference of the object distance and the image distance.

## What is the formula relating focal length object and image distance?

v1+u1=f1.

## How do you find the focal point?

To find the focal point of a parabola, follow these steps: Step 1: Measure the longest diameter (width) of the parabola at its rim. Step 2: Divide the diameter by two to determine the radius (x) and square the result (x ). Step 3: Measure the depth of the parabola (a) at its vertex and multiply it by 4 (4a).

## What is the focal length of concave lens?

The distance between the pole and the principal focus is called the focal length (f) of the lens. The given focal length of the concave lens is f = -2 m. It is negative because a concave lens always has a negative focal length.

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

Solution : From the figure E-7 using sign convention we get

`R_1 = -30cm, R_2 = 60cm and` also given that n = 1.5

using 1/f = (n-1)`(1//R_1 – 1//R_2)`

`1//f = (1.5 – 1)[1//(-30)-1//60]`

Solving this, we get

`f = -120cm`

Here minus indicates that the lens is divergent.

## What is focal length of a concave mirror?

Focal length of a concave mirror it is the distance of the focus from the pole of the concave mirror.

## Is focal length of concave lens negative?

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 combination of convex lens and concave lens?

Hint: When a concave lens and a convex lens of the same focal length are in contact, then the power of the lens combination will be zero and its focal length will be infinite. Therefore, the combination behaves as a plane glass plate.

## What is the focal length of the combination if a lens of focal length 70 cm is brought in contact with a lens of focal length 150 cm What is the power of the combination?

So, net focal length is -131. 25 cm.

## What is f1 and f2 in convex lens?

Answer: f1 is the first focus where the ray of light moves Parralel. f2 is the second focus where the ray of light. appears to get refracted.

## What is the focal length of a lens quizlet?

The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters.

## What is the focal length of a lens What is the focal point quizlet?

D. The distance between the center of the lens and either focal point is the focal length. The focal point is the point where a beam of parallel light, parallel to the principal axis, converges or appears to converge.

## What is focal length in refraction?

Focal length of a lens is the distance between centre of lens and focal point . Focal point is a point on principal axis , at which light rays parallel to principal axis meet after refraction through lens or seem to meet after refraction .

## What is the relation of focal length with refractive index?

Since from lens makers formula we can observe that focal length of lens is inversely proportional to refractive index of medium of lens . Hence net refractive index of lens decreases when it is dipped in a denser medium than air, hence focal length increases.

## How is refractive index and focal length?

Thus, the focal length is inversely proportional to the refractive index. ∴fw>fa where fw is the focal length of the lens in water and fa is the focal length of the lens in air.

## How do you find the focal length of a convex lens without calculating?

Explanation: Place the convex lens in such a position that sunlight is perpendicular to the lens. In such a position sunlight would be parallel to the optical axis of the lens. Place a piece of paper behind and parallel to the lens and adjust its distance from the lens so as to obtain a point image of sunlight.

## How do you find the focal length of a convex mirror using a convex lens?

You can measure the radius of curvature (R) of the mirror by measuring the distance between convex mirror and the screen placed behind the mirror. You can calculate the focal length of the mirror using the equation f = R/2.