What is understood by lateral displacement of light? Illustrate it with the help of a diagram. List any two factors on which the lateral displacement in a particular substance depends.

Q: What is understood by lateral displacement of light? Illustrate it with the help of a diagram. List any two factors on which the lateral displacement in a particular substance depends.

### Lateral Displacement When a ray of light passes obliquely through a rectangular glass slab, it undergoes refraction at two parallel surfaces (air-glass interface and glass-air interface). The emergent ray is parallel to the direction of the incident ray but is shifted sideways. The perpendicular distance between the original path of the incident ray (produced forward) and the emergent ray coming out of the glass slab is called **lateral displacement**. ### Diagram ### Factors on which Lateral Displacement Depends (Any Two): 1. **Thickness of the medium (glass slab):** Lateral displacement is directly proportional to the thickness of the glass slab. A thicker slab produces greater displacement. 2. **Refractive index of the medium:** It is directly proportional to the refractive index of the glass slab. A medium with a higher refractive index bends light more, increasing the displacement. 3. **Angle of incidence:** Lateral displacement increases with an increase in the angle of incidence ($i$).

Light — Reflection and Refraction

Refraction of Light

Official Answer

Lateral Displacement

When a ray of light passes obliquely through a rectangular glass slab, it undergoes refraction at two parallel surfaces (air-glass interface and glass-air interface). The emergent ray is parallel to the direction of the incident ray but is shifted sideways.

The perpendicular distance between the original path of the incident ray (produced forward) and the emergent ray coming out of the glass slab is called lateral displacement.

Diagram

Factors on which Lateral Displacement Depends (Any Two):

Thickness of the medium (glass slab): Lateral displacement is directly proportional to the thickness of the glass slab. A thicker slab produces greater displacement.
Refractive index of the medium: It is directly proportional to the refractive index of the glass slab. A medium with a higher refractive index bends light more, increasing the displacement.
Angle of incidence: Lateral displacement increases with an increase in the angle of incidence ( $i$ ).

lateral displacementperpendicular distanceincident rayemergent raythickness of slabrefractive indexangle of incidence

Marking Scheme

11 mark
21 mark
31 mark

Hint

Think about what happens to light when it enters and exits a parallel-sided glass block. The light shifts sideways but remains parallel to its original direction.

Quick Oral Answer

Lateral displacement is the perpendicular distance by which an emergent ray is shifted from the original path of the incident ray when passing through a parallel-sided refracting medium like a glass slab.

Analysis & Explanation

When light enters a glass slab, it bends towards the normal because it travels from a rarer medium (air) to a denser medium (glass). When it exits the slab, it bends away from the normal by an equal angle because it travels from a denser medium (glass) to a rarer medium (air). Since the two refracting surfaces of the slab are parallel, the angle of incidence equals the angle of emergence ( $i = e$ ). Consequently, the emergent ray is parallel to the incident ray but shifted laterally by a perpendicular distance $d$ . This shift is lateral displacement.

Common Mistakes

1Drawing the emergent ray non-parallel to the incident ray.
2Measuring lateral displacement along the surface of the slab instead of perpendicular to the rays.
3Confusing lateral displacement with the angle of deviation.

Interesting Facts

If a ray of light falls normally (perpendicularly, i.e., $i = 0^\circ$ ) on a glass slab, it passes straight through without any bending, meaning the lateral displacement is exactly zero!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 3 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Light — Reflection and Refraction" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Refraction of Light" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.