11 physics Activity 1. Refractive index of convex lens using spherometer and auto collimation method

 Refractive index of convex lens using spherometer and auto collimation method

Aim:  To determine refractive index of the material of given convex lens.

Apparatus: A spherometer, a metre scale, a double convex lens, a plane mirror, an index pin, a retort stand etc.

Diagram :

Result:

Refractive index of material of the lens, n = 1.35

Precaution

Use the same lens which we have used in spherometer experiment.

Multiple Choice Questions

1. Which principle is the auto-collimation method based on?
   • A) Refraction at a single surface
   • B) Total internal reflection
   • C) The formation of a real image that coincides with the object when the object is at the center of curvature
   • D) Snell's Law
   Answer: C
2. In the auto-collimation method to find the focal length (
   

   $f$
   ) of a convex lens, where should the optical needle be placed to coincide with its inverted image?
   • A) At the focal point (F)
   • B) At the center of curvature (2F)
   • C) At infinity
   • D) Between F and the optical center
   Answer: A
3. The spherometer is used to measure which parameter of the convex lens surface?
   • A) Focal length (f
     

     $f$
     )
   • B) Refractive index (n
     

     $\mu$
     )
   • C) Radius of curvature (R
     

     $R$
     )
   • D) Diameter (D
     

     $D$
     )
   Answer: C
4. Why must the tip of the optical needle and the tip of its image be aligned without parallax?
   • A) To ensure the image is magnified.
   • B) To ensure the image is virtual.
   • C) To confirm that the image is formed exactly at the same horizontal plane as the object, indicating accurate focal length measurement.
   • D) To prevent the lens from moving.
   Answer: C
5. What type of image is formed when the object is placed at the focal point (F) of the convex lens/plane mirror combination in this experiment?
   • A) Virtual and erect
   • B) Real and inverted, at the same position as the object
   • C) Real and enlarged
   • D) No image is formed
   Answer: B
6. If the refractive index of the lens material is 1.5, and it is dipped in a liquid of refractive index 1.5, how will the lens behave?
   • A) As a converging lens
   • B) As a diverging lens
   • C) As a plane glass plate
   • D) The focal length will become negative.
   Answer: C
7. Which source of error is commonly mentioned in this experiment?
   • A) Measuring the diameter of the lens
   • B) Inaccurate measurement of ambient temperature
   • C) Backlash error in the spherometer screws
   • D) Not using a plumb line
   Answer: C
8. The auto-collimation method primarily helps in accurately determining the:
   • A) Radius of curvature
     

     $R$
   • B) Height difference
     

     $h$
   • C) Focal length
     

     $f$
   • D) Distance between outer legs
     

     $l$
   Answer: C

                                  

Quiz