Top 20 Viva Questions on Refractive Index of Water Using Convex Lens and Plain Mirror | Class 12 | Physics | Physics Practical | Viva Questions

Viva Questions with Answers and Explanations

Question: What is the refractive index?
Answer:
It is the ratio of the speed of light in vacuum to its speed in the medium.
Explanation:
The refractive index tells us how much light bends when entering a different medium. A higher index means more bending.

Question: What is the refractive index of water?
Answer:
Approximately 1.33
Explanation:
This means light travels 1.33 times slower in water than in vacuum. It’s a commonly accepted average for visible light.

Question: Which type of lens is used in this experiment?
Answer:
Convex lens
Explanation:
A convex lens is used to focus light rays and form a clear image on the mirror, which is crucial to finding the optical center and focal point.

Question: Why is a plane mirror used below the lens in this experiment?
Answer:
To reflect light rays back through the lens.
Explanation:
The mirror helps reflect the light back through the lens, making it easier to determine the lens's focal point and the image position accurately.

Question: What is the principle used in this experiment?
Answer:
Refraction of light
Explanation:
This practical is based on how light bends or refracts when moving from one medium to another, such as from air to water.

Question: What is the formula for refractive index used here?
Answer:
μ = Real depth / Apparent depth
Explanation:
The refractive index is calculated by comparing how deep an object appears in water versus its actual depth.

Question: Why do we use water in this experiment?
Answer:
To determine its refractive index
Explanation:
Water is a common transparent liquid whose refractive behavior is ideal for studying how light bends at boundaries.

Question: What is the unit of refractive index?
Answer:
It has no unit
Explanation:
Refractive index is a ratio of two similar quantities (speeds), hence it is dimensionless and unitless.

Question: What happens to light when it enters water from air?
Answer:
It bends towards the normal
Explanation:
Light slows down in water, causing it to change direction towards the normal line at the boundary.

Question: What is meant by real depth?
Answer:
Actual depth of the object
Explanation:
Real depth refers to the actual measured distance of the object below the water surface.

Question: What is meant by apparent depth?
Answer:
Depth seen by observer
Explanation:
Due to refraction, objects under water appear closer to the surface than they actually are.

Question: What is optical center of a lens?
Answer:
The central point of lens
Explanation:
The optical center is a point in the lens where light passes without deviation.

Question: Does the refractive index change with wavelength?
Answer:
Yes
Explanation:
The refractive index varies with the wavelength of light due to dispersion.

Question: What is total internal reflection?
Answer:
Light reflects entirely within medium
Explanation:
It occurs when light hits the boundary at an angle greater than the critical angle and reflects entirely inside.

Question: What happens if lens is not placed correctly?
Answer:
Image will be distorted or unclear
Explanation:
Improper alignment affects image clarity and focal measurements, leading to inaccurate results.

Question: What is the shape of a convex lens?
Answer:
Thicker at the center
Explanation:
A convex lens bulges out at the center and converges light rays to a point.

Question: Can we use any liquid for this experiment?
Answer:
Yes, if it is transparent
Explanation:
Any transparent liquid like water, oil, or alcohol can be used to observe light refraction.

Question: Why do we use white light in this experiment?
Answer:
Easier to observe image
Explanation:
White light offers better visibility and contrast while observing real and apparent images.

Question: What will happen if mirror is not properly cleaned?
Answer:
It will blur the image
Explanation:
Dirt or dust on the mirror scatters light, reducing clarity and precision in locating images.

Question: What happens to the refractive index with temperature?
Answer:
It decreases
Explanation:
As temperature increases, the density of the liquid reduces, slightly lowering the refractive index.

Question: What should be the lens focal length for accurate reading?
Answer:
15 to 20 cm
Explanation:
This range provides a clear, measurable image and is ideal for practical setups using plane mirrors.

Question: What happens to the focal length of the lens when placed in water?
Answer:
It increases
Explanation:
Due to the lower refractive contrast between water and the lens material, the bending of light is reduced, increasing focal length.

Conclusion

This Physics practical not only demonstrates the concept of refraction but also teaches measurement techniques using basic optical tools. Tools used include a convex lens, a plane mirror, water, a stand, and a scale. Students must ensure correct placement of the lens and mirror, clean the surfaces, and take repeated readings for accuracy. Avoid parallax errors and handle the lens with care to avoid scratches or misalignment.

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