Viva Voce: Refraction Through Glass Slab | Lab Manuals for Class 10 PDF Download

Q.1. When a ray of light refracts through glass slab with parallel surfaces, what is the difference between angle of incidence and angle of emergence?

When a ray of light refracts through glass slab with parallel surfaces, then the difference between angle of incidence and angle of emergence is zero.

Q.2. Define an angle of emergence.

The angle made by the emergent ray with the normal to the glass-air interface is called an angle of emergence. It is denoted by ∠e.

Q.3. What distance should be maintained between the pins P₁ and P₂ or P₃ and P₄ to obtain the accurate result?

The distance between the pins should be maintained at 5cm, to obtain the accurate result.

Q.4. Give the relation between angle of incidence (∠i), angle of refraction (∠r), angle of emergence (∠e), in this experiment.

In this experiment, the relations between ∠i, ∠r and ∠e are ∠e = ∠i and ∠r < ∠i

Q.5. While tracing the path of ray of light through a glass slab, the angle of incidence is generally taken between 30° and 60°. Explain the reason on the basis of your performing this experiment for different angles of incidence. 

These are following reasons:

• If the angle of incidence is less than 30°, bending of light at glass-air interface will be very less.
• If the angle of incidence is greater than 60°, then emergent ray may emerge from the side surface as angle of emergence also increases with the increase in angle of incidence or vice-versa.

Q.6. Why does a ray of light bend towards the normal, when it enters from air into glass slab and bends away from the normal, when it emerges out into air?

It bends towards the normal, when it travels from rarer to denser medium or speed of light decreases in denser medium and vice-versa.

Q.7.  State some precautions that one should take while performing the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different values of angle of incidence.

• Pins should be fixed exactly vertically.
• Angles should be fixed between 30° and 60°.
• Glass slab should be placed well within the outline marked.

Q.8. Why is it necessary to observe the feet of the pins for collinearity of the points in this experiment?

The pins fixed on the sheet of paper may not be exactly perpendicular to the plane of paper. Thus, if their heads appear to be collinear, their feet may not be. So, it is important to observe the collinearity by looking at the feet.

Q.9. What happens to the refraction angle, when angle of incidence decreases?

On decreasing angle of incidence, angle of refraction also decreases.

Q.10. How does the lateral displacement of the emergent ray depend on the width of the glass slab and angle of incidence? 

Lateral displacement is directly proportional to the width or thickness of the glass slab. It is also directly proportional to the angle of incidence.

Q.11.  Draw the path of a ray of light, when it enters perpendicular to the surface of a glass slab. 

Q.12. Why are the incident and emergent rays parallel to each other, in case of refraction though a rectangular glass slab? 

As the angle of incidence (∠i) is equal to the angle of emergence (∠e) in case of glass slab, so incident ray is parallel to emergent ray.