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# Physics Practical Class 12 - To determine the refractive index of a glass slab using a travelling microscope. Viva Questions with Answers

1) What is the depth of focus in a microscope?

The distance between the objective lens and the model plane in a microscope is known as its depth of focus. The depth of focus differs from person to person, and also it depends on the quality of focus.

2) What is the depth of field in a microscope?

The distance from the farthest plane in focus to the nearest object plane in the same focus is known as the depth of field in a microscope. In microscopes, the depth of field is measured in units of microns because it is very short.

3) What is the field of view in a microscope?

The diameter of the circle, which is illuminated and is seen through the eyepiece in a microscope, is known as its field of view. There is a decrease in the field of view with an increase in the magnification.

4) What is a refractive index?

When a light ray passes from a medium to some other medium, then the measurement of bending of that light ray is known as the refractive index. It can be expressed as n = c/v.

5) What is the formula to calculate the refractive index of a medium?

The following formula can be used to compute the refractive index of a medium:

n = c/v

where, the refractive index of the medium is denoted by ‘n’

the velocity of light in a vacuum is denoted by ‘c’

the velocity of light in the medium is denoted by ‘v’

6) Is the speed of light faster in glass or water?

As compared to glass, the speed of light is faster in water since the refractive index of glass is 1.5, and the refractive index of water is 1.3. According to the equation n = c/v, we know that the refractive index of a medium and the velocity of light in that medium is inversely proportional to each other. Hence light travels faster in water.

7) What is the normal shift?

There exists an apparent shift in the position of an object when placed in a particular medium and viewed along the normal from another medium, and this shift is known as the normal shift.

8) What is the apparent shift?

The difference between the distance of the object and the distance of the image from the refracting surface is known as apparent shift.

9) What are the sources of error in the experiment – To determine the refractive index of a glass slab using a travelling microscope.

• It may be possible that the scale used in the microscope might not be adjusted properly.
• Thin lycopodium powder layer on the glass slab.

10) On what factors does apparent depth depend?

Apparent depth depends on the following factors:

• The thickness of the medium
• Nature of the medium
• Colour of the light