Question

How do you find out the local length of the
convexlens. write procedure & precation,​

Answer 1

Hope it helps

If appropriate answer mark branliest

Procedure

To determine the rough focal length of the convex lens

Place the convex lens on the lens holder.

Now face the lens towards a distant tree or building.

Obtain the image either on the white wall or on a screen and keep moving the lens either forward or backwards till a sharp image is formed.

To determine the rough focal length of the lens, measure the distance between the lens and the screen.

To set the convex lens

Place the lens on the holder with fixed upright such that the upright is kept at 50 cm mark.

The lens should be placed in such a way that its surface is vertical and perpendicular to the length of the optical bench.

The upright should be kept in this position throughout.

To set the object needle

Place the thin optical needle which is the object needle O near-zero end of the upright which is moveable.

Place the object needle upright at a distance nearly 1.5 times the focal length of the lens.

The tip of the needle should be horizontal to the optical centre of the lens.

Note the position of the index mark below the object needle upright.

To see an inverted and enlarged image of the object needle which is in the middle of the lens, close the left eye and see with a right eye open.

On the other end of the optical bench, place the image needle on the fourth upright.

The tip of the image needle should be in line with the image that is seen with the right eye.

To see the parallax, move the eye towards the right. The image needle and object needle are no longer in line.

Remove the parallax tip to tip.

Note the position of the index mark at the base of the image needle upright.

Record the position of the index marks.

Now place the concave lens holder on the I side of the convex 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.

To set the image needle at I’

Repeat steps 4 and 5.

To get more observations

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.

Record all the observations.

Observations

The rough focal length of a convex lens = ……….

The actual length of the knitting needle, x = ………

Observed distance between the concave lens and image = ……..

Needle when knitting needle is placed between them, y = ……..

Index correction for u as well as v, x – y = ……..

Table for u, v and f

Sl. no Position of Observed Corrected f=uvu−v in cm

O in cm L1 at O1 in cm I in cm L2 at O2 in cm I’ in cm u = IO2 in cm v = I’O2 in cm u in cm v in cm

1. f1=

2. f2=

3. f3=

Calculations

To find observed u by finding the difference of position of L2 and I.

To find observed v by finding the difference of position of L2 and I’.

Corrected values of u and v are obtained by applying index correction.

Calculate f=uvu−v.

Finding the mean of f

Meanf=f1+f2+f33

Result

The focal length of the given concave lens = …….. cm