Physics Class 10 Practical 24 Important Viva Questions with Answers (To determine the critical angle of glass using a semi circular slab and a light ray box/or by prism)

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Viva Questions and Answers

Question1: What is the critical angle? 

Answer: The critical angle is the angle of incidence in the denser medium at which the angle of refraction in the less dense medium becomes 90 degrees.

Question 2: Why is a semi-circular slab used in this experiment? 
Answer: A semi-circular slab is used because it ensures that the light ray enters the slab perpendicularly to the flat surface, avoiding refraction at the point of entry and simplifying the observation of the critical angle.

Question 3: What is total internal reflection? 
Answer: Total internal reflection is the phenomenon where a light ray, traveling from a denser medium to a less dense medium, is completely reflected back into the denser medium when the angle of incidence exceeds the critical angle.

Question 4: How do you determine the critical angle using a semi-circular slab? 
Answer: Shine a light ray into the flat surface of the semi-circular slab. Gradually increase the angle of incidence until the refracted ray along the curved surface is no longer visible and only the reflected ray is seen. The angle of incidence at this point is the critical angle.
sin C = 1/n

Question 5: What is the relationship between the critical angle and the refractive index of the material? 
Answer: The critical angle (C) is related to the refractive index (n) of the material by the equation .
n=1/sinC where C is the critical angle.

Question 6: Why does total internal reflection occur only when light travels from a denser to a less dense medium? 
Answer: Total internal reflection occurs only when light travels from a denser to a less dense medium because only in this situation can the angle of refraction reach 90 degrees or more, causing the light to be reflected back entirely.

Question 7: How can you calculate the refractive index of the glass using the critical angle? 
Answer: The refractive index (n) of the glass can be calculated using the formula

Question 8: What is the role of the light ray box in this experiment? 
Answer: The light ray box provides a narrow, collimated beam of light, which makes it easier to observe and measure the angles of incidence and reflection accurately.

Question 9: How would you determine the critical angle using a prism? 
Answer: Direct a light ray into one face of the prism and observe the emerging ray from the other face. Gradually adjust the angle of incidence until the emerging ray is exactly at 90 degrees to the normal. This angle of incidence inside the prism is the critical angle.

Question 10: What are some practical applications of the concept of the critical angle? 
Answer: Practical applications include optical fibers, where total internal reflection is used to transmit light signals over long distances with minimal loss, and in certain types of lenses and prisms used in optical instruments.

Question 11: Why is it important for the incident ray to strike the flat surface of the semi-circular slab perpendicularly? 
Answer: Striking the flat surface perpendicularly ensures that there is no refraction at the air-glass interface, which simplifies the determination of the critical angle by focusing only on the glass-air interface.

Question 12: Can the critical angle be measured for light traveling from air to glass? 
Answer: No, the critical angle can only be measured for light traveling from a denser medium (glass) to a less dense medium (air). There is no critical angle when light travels from air to glass because it bends towards the normal.

Question 13: How does the wavelength of light affect the critical angle? 
Answer: The critical angle is dependent on the refractive index, which varies with the wavelength of light. Typically, the refractive index is higher for shorter wavelengths (blue light) and lower for longer wavelengths (red light), resulting in different critical angles for different colors.

These questions cover the basic concepts and practical understanding required to perform the experiment and explain the phenomena involved in determining the critical angle of glass.