Introduction to Tracing the Path of a Ray
Among the various properties of light, reflection and refraction are two of the most important aspects. In this chapter, you are going to study in detail about these two properties with the help of specific situations and conditions.Out of them, the experiment for refraction through glass slabs is the most vital. Before delving deeper into this experiment and its conclusions, students should have prior knowledge of its concept. Having clarity on the two properties of light is crucial to gain a stronghold on the advanced concepts.
Tracing the Path of a Ray of Light - Free PDF
So, let us understand these properties first. Reflection and Refraction Look at the image below to understand refraction through glass slab -
The image here shows both the reflected and refracted rays. It presents the rays during reflection and also during refraction of light through the glass slab. As the name implies, a reflected ray is the one which deviates at the same angle in which it falls on a surface. On the other hand, during refraction through a glass slab, the ray passes through this surface. Once it has passed this surface, it deviates at an angle different from the one at which it fell.There are a few common phenomena which show both reflection and refraction of light through a glass slab.
Herein, students have to be clear about both terms and also angles at which a ray is incident on a surface. Law of ReflectionStudents should note here that during reflection, a light ray travels in the same medium. In simple words, the ray is incident and reflected in a common medium, say air. However, the observation of refraction of light indicates that there is a change in angle.It means, during refraction, light rays change their path. In other words, they deviate from their angle of incidence when they change their medium of travel.This is where the glass slab experiment must be understood by students since it proves these phenomena discussed above. However, before shifting to the experiment, you should know about the laws of reflection, which states -‘Reflected ray, normal and incident ray lie on a common plane.’‘Ratio of sine of an incident ray to the sine of reflected ray is constant.’
sine i/ sine r = k
Herein, i is angle of incidence, r is angle of reflection, and k is a constant.
To conduct an experiment of tracing the path of a ray of light passing through a rectangular glass slab, students will have to get a clear understanding of chapter 9 called ray optics and optical instruments of the NCERT book of class 10. This chapter is extremely important in the study of physics and it is prescribed by the Central Board of secondary education and therefore holds significant weightage in the board examinations that are held at the end of the term by the CBSE. This chapter mainly discusses the main properties of light that are reflection and refraction. Students wanting to get a clear understanding of the concept in a simplified language can refer to Vedantu, this website contains all the necessary information and concepts that students need to go through before the board examination, as it contains the latest CBSE curriculum so that students can be up-to-date with the syllabus and therefore can prepare accordingly.
In order to perform the experiment of tracing the path of a ray of light passing through a rectangular glass slab students need to go through the concepts of reflection and refraction, laws of reflection, refraction through a glass slab. These concepts are discussed in detail on Vedantu’s website. All the study material on Vedantu is available for free and can be downloaded in PDF format. The PDF format will enable students to study in an offline environment which is extremely important during the examination phase.
Experiment
Aim-
To trace the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Measure the angle of incidence, angle of emergence, angle of refraction and interpret the result.
Theory-
What are the laws of refraction?
The incident ray, the normal ray, and the refracted ray, all lie in the same plane.
Snell’s law: The law states that the ratio of the sine of an angle of incidence to the sine of the angle of refraction is constant. Sin i/sin r = constant.
Materials Required-
Glass slab
Drawing board
White paper
Six pins
Scale and protractor
Pencil
Thumb pins
Procedure-
Fix the white sheet on a drawing board with thumb pins.
Outline a glass slab and label it ABCD.
Draw a perpendicular on one side and label it as normal EP on side AB.
Draw an angle of 30° and fix two pins 3 or 4 cm apart on this line.
See through the glass slab and place these other two pins on the other side of this slab.
Make sure that all four pins are in a straight line.
Mark those four points with a circle.
Remove the glass slab and join the dots.
Conclusion-
The angle of emergence and the angle of incidence is almost equal
The angle of refraction will be lesser than the angle of incidence as the light is traveling from rarer to a denser optical medium
The lateral displacement will remain the same for different angles of incidence
Light bends towards the normal when it travels from an optically rarer medium to an optically denser medium.
Sources of Error-
The glass slab should not have any air bubbles
The measurements made using the protractor should be accurate.
Key Elements Important in the Understanding of the Experiment-
Tracing the path of a ray of light passing through a rectangular glass slab.
Particle model of light,
reflection of light by spherical mirrors,
sign convention,
The focal length of spherical mirrors,
the mirror equation,
refraction,
Snell’s law,
total internal reflection,
total internal reflection in nature and its technological applications,
refraction at spherical surfaces and balances,
refraction at a spherical surface,
Light sources and photometry,
refraction by a lens,
power of a lens,
combination of thin lenses in contact,
refraction through a prism,
dispersion by a prism,
some natural phenomena due to sunlight,
the rainbow,
scattering of light,
optical instruments,
the eye,
the microscope,
Telescope,
FAQs on Tracing the Path of a Ray of Light Passing Through a Rectangular Glass Slab
1. What happens when a ray of light passes through a rectangular glass slab?
When a ray of light travels from a rarer medium (like air) into a denser medium (like glass), it undergoes refraction. The ray bends towards the normal at the first surface. As it exits the glass slab and re-enters the air, it refracts again, this time bending away from the normal. The final emergent ray is parallel to the initial incident ray but is shifted sideways.
2. What is lateral displacement and why does it occur in a glass slab?
Lateral displacement is the perpendicular shift in the path of light as it emerges from a refracting medium like a glass slab. It occurs because the light ray refracts, or bends, at two parallel surfaces. The bending at the first surface (air-to-glass) is cancelled out by the opposite bending at the second surface (glass-to-air), causing the final ray to be parallel but shifted.
3. Why is the emergent ray parallel to the incident ray in the glass slab experiment?
The emergent ray is parallel to the incident ray because a rectangular glass slab has two parallel refracting surfaces. The amount of bending the light ray undergoes upon entering the slab is equal and opposite to the amount it bends upon exiting. This geometric property ensures that the final direction of the light ray is the same as its initial direction, making the angle of incidence (i) equal to the angle of emergence (e).
4. On what factors does the amount of lateral displacement depend?
The amount of lateral displacement a light ray experiences depends on three key factors:
- Thickness of the glass slab: A thicker slab will cause a greater lateral displacement.
- Angle of incidence: The lateral displacement increases as the angle of incidence increases.
- Refractive index of the glass: A higher refractive index causes the light to bend more, resulting in a larger lateral displacement.
5. What would be observed if the incident ray strikes the glass slab perpendicularly?
If an incident ray of light strikes the glass slab perpendicularly (at an angle of 90° to the surface), its angle of incidence is 0°. In this specific case, the light ray will not bend or deviate from its path. It will pass straight through the glass slab without undergoing any refraction or experiencing any lateral displacement.
6. How does Snell's Law apply to tracing a ray through a glass slab?
Snell's Law is the fundamental principle governing the experiment. It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, which is the refractive index of the medium. When tracing the path, we apply Snell's Law at both surfaces: first at the air-glass interface and then at the glass-air interface, to determine the exact path of the refracted and emergent rays.
7. What is the difference between the angle of refraction and the angle of emergence?
The angle of refraction (r) is the angle between the refracted ray and the normal inside the glass slab. The angle of emergence (e) is the angle between the emergent ray and the normal as the ray exits the slab. For a rectangular glass slab, the angle of emergence is always equal to the angle of incidence (i), whereas the angle of refraction is different, determined by Snell's Law.
8. What is the real-world importance of understanding refraction through a medium like glass?
Understanding refraction is crucial for the functioning of all optical instruments. It is the principle behind how lenses in eyeglasses, cameras, telescopes, and microscopes work to focus light and form images. It also explains common observations, such as why a straw in a glass of water appears bent or why the bottom of a swimming pool looks shallower than it really is.
