CBSE Physics Project by syed.husam on emaze

CBSE Physics Project

Refractive Indices of Water, Oil, and Glycerol

Syed Husam 12-E

Draft

Table of Contents

Objective

Introduction

Apparatus

Diagram

Theory

Procedure

Observations

Calculations and Result

Precautions and Sources of Error

1

2

3

4

5

6

7

8

9

Objective

To find the refractive indices of water, oil and glycerol using a plane mirror, equiconvex lens (made form glass of known refractive index) and an adjustable object needle.

Apparatus

A convex lens, a plane mirror, water, oil, glycerol, clamp, stand, an optical needle, knitting needle, half meter scale, glass slab, spherometer.

Introduction

In optics the refractive index n of an optical medium is a dimensionless number that describes how light, or any other radiation, propagates through that medium. The refractive index determines how much light is bent, or refracted, when entering a material. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection. It varies with the wavelength of light. The concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound.

Theory:-

Focal length

If f1, f2 and f are the focal lengths of convex lens, liquid lens and combination respectively, then, 1/f=1/f1 +1/f2 or f2=(ff1)/(f1-f)

Refractive Index

Liquid lens forms a plano-concave lens with R1=R and R2=∞, then refractive index of liquid (n) from lens maker formula is, n=(R/f2)+1

Radius of Curvature

The radius of the lower surface of the convex lens is given from the formula of spherometer, as, R=(l^2/6h) + (h/2)

Diagram

Procedure

Focal length of convex lens.

Find the rough focal length.
Place the plane mirror on horizontal base of iron stand and then convex lens on it.
Hold the needle on the clamp and adjust its position such that there is no parallax between tip of needle and its image.
Measure the distance between tip and upper surface of the lens and also the distance between tip and upper surface of the mirror.
Take the mean of these two distances which will be equal to the focal length of convex lens (f1).

Focal length of combination.

Put a few drops of water on mirror and place the convex lens on it so that water spreads and acts as a plano-concave lens.
Determine the equivalent focal length of the combination.
Repeat the same for oil and glycerol.

Determine the radius of curvature (R) of convex lens surface using a spherometer.

Observations

1) Rough focal length of convex lens = ........... cm.

2) Table for focal lengths of lens and combinations.

Arrangement

Distance of needle tip from (in cm)

Lens surface (x1)

Plane mirror (x2)

Mean distance (x)

Focal length (cm)

Without liquid

With water

With oil

With glycerol

f1 = ..........

fw = ..........

fo = ..........

fg = ..........

3) Table for spherometer reading h.

Sr. no.

Initial C.S.R. on convex lens

(a)

No. of complete rotations

(n)

Final C.S.R. on plane mirror

(b)

m=(a-b) or (100+a-b)

h=(n*pitch)+(m*L.C.)

1.

2.

3.

Mean value of h = ............ cm.

Calculations

l = (l1 + l2 + l3)/3 = ............... cm.
R = (l^2/6h) + (h/2) = ............... cm.
f2 = (ff1)/(f-f1) = ............... cm.
n = 1 + R/f2 = ............... cm.

Results

The refractive index of water nw = ............... cm.
The refractive index of oil no = ............... cm.
The refractive index of glycerol ng = ............... cm.

Precautions

The plane mirror should be clean and fully shining surface.
The liquid taken should be transparent.
The tip to tip parallax should be removed,
The legs of spherometer should be vertical.
Only few drops of the liquid to be taken so that the layer is thick.

Sources of Error

Liquid may not be quite transparent.
The parallax may not be fully removed.
The legs of spherometer should be placed symmetrical on the surface of the convex lens.
The tip of central screw should just touch the surface of the lens or mirror.