To find Refractive Indices of Water And
To find Refractive Indices of Water And Turpentine Oil using a plane mirror, a equiconvex lens (made from a glass of known refractive index) and an adjustable object needle
APPARATUS:
A convex lens, an optical needle, a plane mirror, a clamp stand, a spherometer, a plumb line, metre scale, water and turpentine oil
Theroy :
Let's add small amount of water on a flat, plane surface and place a convex lens over it. This forms a plano-concave lens of water between the lower surface of convex lens and plane mirror.
Let f 1 and f 2 are the focal lengths of water lens and convex lens respectively, then focal length of the combination is:
The focal length of the plano-concave lens is, …(i)
From Lens Maker's formula,
=(
R 1 = R and R 2 = for water lens. The refractive index of water is , …(ii)
(where ‘R' is the radius of curvature of the concave surfaces of the plano-concave lens).
The Radius of curvature of the lens, is
…(iii)
PROCEDURE
• For finding the focal length of convex lens:
• Measure the rough focal length of the convex lens.
• Place the plane mirror with the convex lens placed on it above the horizontal base of a clamp stand horizontally as its tip lies vertically above the optical centre of the lens. Adjust the needle at a height a little more than the rough focal length of the convex lens.
• Try to remove the parallax between the tip of the object needle and its image tip.
• Note the distance of the tip of the needle from the centre of the upper surface of the lens. Let it be x 1. (Use plumb line).
• Remove the convex lens and measure the distance of the tip of the needle from the plane mirror. Let it be x 2 . (Use plumb line).
2 (vi) Repeat and record all the observations.
• For finding the focal length of the plano-concave lens:
Pour few drops of water over the plane mirror and place the convex lens over it. Repeat steps (ii) to (iv) as done above.Repeat the procedure with turpentine oil also.
• For finding ‘l':
Determine the pitch and least
APPARATUS:
A convex lens, an optical needle, a plane mirror, a clamp stand, a spherometer, a plumb line, metre scale, water and turpentine oil
Theroy :
Let's add small amount of water on a flat, plane surface and place a convex lens over it. This forms a plano-concave lens of water between the lower surface of convex lens and plane mirror.
Let f 1 and f 2 are the focal lengths of water lens and convex lens respectively, then focal length of the combination is:
The focal length of the plano-concave lens is, …(i)
From Lens Maker's formula,
=(
R 1 = R and R 2 = for water lens. The refractive index of water is , …(ii)
(where ‘R' is the radius of curvature of the concave surfaces of the plano-concave lens).
The Radius of curvature of the lens, is
…(iii)
PROCEDURE
• For finding the focal length of convex lens:
• Measure the rough focal length of the convex lens.
• Place the plane mirror with the convex lens placed on it above the horizontal base of a clamp stand horizontally as its tip lies vertically above the optical centre of the lens. Adjust the needle at a height a little more than the rough focal length of the convex lens.
• Try to remove the parallax between the tip of the object needle and its image tip.
• Note the distance of the tip of the needle from the centre of the upper surface of the lens. Let it be x 1. (Use plumb line).
• Remove the convex lens and measure the distance of the tip of the needle from the plane mirror. Let it be x 2 . (Use plumb line).
2 (vi) Repeat and record all the observations.
• For finding the focal length of the plano-concave lens:
Pour few drops of water over the plane mirror and place the convex lens over it. Repeat steps (ii) to (iv) as done above.Repeat the procedure with turpentine oil also.
• For finding ‘l':
Determine the pitch and least