pHYSICS

Experiment 8

Aim of the Experiment

To determine the refractive index of a liquid using convex lens by parallax method.

Principle

In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as:

n = c/v

where, c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water.

The refractive index determines how much light is bent, or refracted, when entering a material. When light moves from one medium to another, it changes its direction, i.e., it is refracted.

Materials required

The given convex lens, The given liquid- water, Plane mirror, Retort stand, Pointer, Mercury, Meter scale, China dish.

Procedure

Simulator Procedure (as performed through the Online Labs)

Select the convex lens from the drop down list.

Select the method from the drop down list.

Without Liquid

• Select the distance of the pointer from the bottom of the lens using the slider (Object pointer).

• You can see that the size of the image varies with distance.

• Adjust the pointer so that the image coincides with the tip of the object without parallax. At this stage, the image and object will be of the same size.

• You can see the zoomed view of the object (left) and image (right) on the right side.

• You can view the object and image from different angles of view (left, centre and right) using the slider.

• Measure the height of the pointer from the bottom of the lens. It is taken as y2 cm.

• The thickness of the lens is t cm.

• You can calculate the distance of the pointer from the top of the lens (y1) using the equation, y1 = (y2 -t) cm.

• You can calculate the focal length (f1) of the convex lens using the equation,

• f1 =y1+y2 /2

• You can verify your result by clicking on the “Show result’ button.

With Liquid

• Select the liquid from the drop down list.

• Select the distance of the pointer from the bottom of the lens using the slider (Object pointer).

• You can see that the size of the image varies with the distance.

• Adjust the pointer so that the image coincides with the tip of the object without parallax. At this stage, the image and object will be of the same size.

• You can see the zoomed view of the object (left) and image (right) on the right side.

• You can view the object and image from different angles of view (left, centre and right) using the slider.

• Measure the height of the pointer from the bottom of the lens. It is taken as y2 cm.

• The thickness of the lens is fixed as t cm.

• You can calculate the distance of the pointer from the top of the lens (y1) using the equation, y1 = (y2 -t) cm.

• You can calculate the focal length (F) of the convex lens using the equation,

• F =y1+y2 /2

• You can calculate the focal length of the liquid lens (f2) using the equation,

• f2 =F* f1 / f1 - F

• The radius of curvature of the lens is R cm.

• You can calculate the refractive index of the liquid using the equation,

• n(i) = 1 + R/f2

• You can verify your results by clicking on the ‘Show result’ button.

Observation Table

Calculation:

focal length of the liquid lens, = ----------cm

The distance of the pointer from the center of the lens = ---------------cm

Radius of curvature of the lens, = -----------cm

Refractive index of given liquid, = --------------

Result

The refractive index of the given liquid by liquid lens arrangement = ----------------

Reference Material

1. University Physics, Ronald Lane Reese, 2003, Thomson Brooks/Cole

2. Virtual Lab on Discharging of Capacitor

3. Virtual Lab on Charging of Capacitor

Questions

1. The bending of a beam of light when it passes obliquely from one medium to another is known as _______.

2. What type of lens is formed when a convex lens is placed over some drops of the given liquid on a plane mirror?