Show lateral deviation of a beam of light incident obliquely on a glass slab.
Show Hint
To clearly observe the lateral shift, use a thicker glass slab and a larger angle of incidence (but less than 90 degrees). The greater the thickness and the angle of incidence, the greater the lateral deviation.
Step 1: Understanding the Concept:
When a ray of light passes obliquely through a rectangular glass slab with parallel faces, it emerges parallel to its original path. However, the emergent ray is shifted sideways. This perpendicular distance between the direction of the incident ray and the emergent ray is called lateral deviation or lateral shift. This phenomenon occurs due to refraction at the two parallel surfaces of the slab. Step 2: Apparatus Required:
- A rectangular glass slab
- A drawing board and a sheet of white paper
- Drawing pins or tape
- Several all-pins
- A protractor and a ruler Step 3: Ray Diagram and Procedure: Ray Diagram:Procedure:
1. Setup: Fix the sheet of paper on the drawing board. Place the glass slab in the middle and trace its outline, labeling it ABCD.
2. Incident Ray: Remove the slab. Draw a line PQ that meets the face AB at an angle (the incident ray). Fix two pins, P1 and P2, vertically on this line.
3. Locating Emergent Ray: Place the slab back on its outline. Look through the opposite face CD and place two more pins, P3 and P4, such that they appear to be in a straight line with the images of pins P1 and P2.
4. Tracing the Path: Remove the slab and the pins. Join the points P3 and P4 to form the line RS, which is the emergent ray. Join the point Q on face AB to the point R on face CD. The path P-Q-R-S is the path of the light ray.
5. Observing Deviation: Extend the incident ray PQ forward with a dashed line. You will observe that the emergent ray RS is parallel to the extended incident ray. The perpendicular distance between these two parallel lines is the lateral deviation. Step 4: Result:
The experiment demonstrates that a ray of light incident obliquely on a glass slab emerges parallel to its original path but is displaced laterally.
