Ray Optics is a branch of optics that describes light propagation in the form of rays. Ray Optics is also called geometrical optics which deals with the geometry of falling lights. this article is about refraction, its laws, refraction through glass slab and its various causes, and practice tracing the path of light rays passing through glass slab. Refraction is the property of the change in direction of the wave while entering from one medium to another medium. This change in direction is due to a change in the speed of the wave. Show What is Refraction?
The wave bends because of the change in its speed from one medium to another medium. Here are two laws of Refraction that can be stated as:
sin i / sin r = constant
Some important properties of a glass slab can be stated as:
Refraction through the Glass Slab
Therefore, the formula for the lateral displacement d is given by, d = [t sin(i – r)]/ cos r = t sin(i – r) sec r where t is the thickness of the glass slab, i is the angle of incidence, r is the angle of refraction. Experiment to Trace the path of a ray of light passing through a glass slabAim: Tracing the path of a ray of light passing through the glass slab. Materials Required:- Drawing board, all pins, white paper, rectangular glass slab, protractor, scale, pencil, thumb pins. Procedure:
Conclusion:
Case 1: Refraction when the object is in a denser medium and the observer is in a rarer medium Consider a glass slab with refractive index and thickness μ and t respectively. The observer (eye) is in the air and the object (O) is in the glass slab. Hence for this case, Virtual Depth = t / μ and Virtual displacement (OI) = OA – AI = t[1-(1/ μ)] Case 2: Refraction through the successive slabs with different thicknesses and refractive index Consider three successive slabs s1, s2, and s3 with thickness t1, t2, t3, and refractive indices μ1, μ2, and μ3 respectively. These slabs are arranged one after the other with s1 at the top, s2 at the middle, and s3 at the bottom. The object(O) is in s3 and the observer (eye) is outside in the air (rarer medium). Hence for this case, Virtual depth (AI) = (t1/ μ1) + (t2/ μ2) + (t3/ μ3) + ……. and Virtual displacement (OI) = t1[1 – (1/ μ1)] + t2[1 – (1/ μ2)] + t3[1 – (1/ μ3)] + ……… Case 3: Refraction when object and observer both are in a rarer medium Consider a glass slab with thickness t and refractive index μ. In this case, the object (O) and observer(eye) both are in a rarer medium (air) separated by the glass slab. Hence for this case, Virtual displacement (OI) = [t – (1/ μ)] Case 4: Refraction when the object is in a rarer medium and the observer is in a denser medium Consider the observer(eye) is in water(denser medium) and the object (O) is in the air (rarer medium). Hence for this case, Real height / Virtual height = 1 / μ or Virtual displacement (OI) = AI – AO = (μ – 1)AO Sample QuestionsQuestion 1: Determine the position of the object kept at bottom of the glass slab with the thickness of 12 cm and the refractive index of glass is 1.5. Answer:
Question 2: Two immiscible liquids of refractive indices 3/2 and 4/3 filled in the vessel up to 9 cm and 12 cm then, What will be the virtual depth of the bottom of the vessel. Answer:
Question 3: An object is kept at the bottom of the empty vessel and a microscope is focused to observe it. Now, water is filled in it up to 16cm then, at what amount microscope should move so that it can again focus on the object. The Refractive index is 4/3. Answer:
Question 4: An air bubble in a glass slab (μ = 1.5) is 5 cm deep when viewed from one face and 2cm deep when viewed from the opposite face then find the thickness of the slab. Answer:
Question 5: What is lateral displacement. State the factors on which it depends. Answer: The perpendicular distance between the incident ray and the resulting emergent ray is called the lateral displacement. Factors on which lateral displacement depends:
Question 6: Why emergent ray is parallel to the incident ray in the refraction through the glass slab. Answer:
Question 7: Find the lateral displacement when refraction through a glass slab takes place where the angle of incidence is 45° and angle of refraction is 30° and the thickness of the glass slab is 10 cm. Answer:
|