# AP Board 10th Class Physical Science Notes Chapter 4 Refraction of Light at Curved Surfaces

Students can go through AP State Board 10th Class Physical Science Notes Chapter 4 Refraction of Light at Curved Surfaces to understand and remember the concept easily.

## AP State Board Syllabus 10th Class Physical Science Notes Chapter 4 Refraction of Light at Curved Surfaces

→ The lens is an optical system with two refracting surfaces.

→ The lens which is thicker at its centre than edges is called a convex (or) converging lens.

→ The lens which is thicker at its edges than the centre is called a concave (or) diverging lens.

→ The lemon in the water of the glass tumbler appears bigger than its actual size when viewed from the sides of the tumbler due to refraction.

→ The relation between refractive indices of media, object distance, image distance and radius of curvature is given by
$$\frac{n_{2}}{v}-\frac{n_{1}}{u}=\frac{\left(n_{2}-n_{1}\right)}{R}$$

→ In the case of plane surfaces, R & f are infinity. Power is equal to zero.
∴ $$\frac{n_{2}}{v}=\frac{n_{1}}{u}$$

→ Each curved surface of a lens is part of a sphere.

→ The centre of the sphere which contains the part of the curved surface is called the centre of curvature.

→ The midpoint of the lens is called a pole (or) optical centre.

→ The point from which rays seem emanating is called focal point or focus (F). (or) The point where rays converge is called the focal point of focus.

→ Every lens has two focal points.

→ The distance between the focal point and pole is called focal length which is denoted by f.

→ The line that joins the centre of curvature and the pole is called the principal axis.

→ The distance between the centre of curvature and pole is called the radius of curvature (R).

→ Any ray passing through the principal axis is un-deviated.

→ Any ray passing through the pole is also un-deviated.

→ The rays passing parallel to the principal axis converge at focus or diverge from focus.

→ The ray passing through the focus of the convex lens will take a path parallel to the principal axis after refraction.

→ When parallel rays fall on the lens making a certain angle with the principal axis the rays converge at a point or appear to diverge from a point lying on a focal plane.

→ If the size of the image is larger than that of an object, it is called a magnified image.

→ Lens formula is $$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$$
v = image distance
u = object distance
f = focal length.

→ Lens maker formula is $$\frac{1}{f}$$ = (n -1)$$\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$$
n is the absolute refractive index
R1 R2 are radii of curvature.

→ Lens: A lens is formed when a transparent material is bounded by two spherical surfaces.

→ Focal Length (f) The distance between the focal point and optic centre (pole) is called the focal length of the lens. It is denoted by f.

→ Focus (F): The point of converging lar) the point from which rays seem emanating is called focal point or focus.

→ The optic centre or Pole (P): The midpoint of a thin lens is called a pole or optical centre.

→ Principal axis: The line joining the centre of two curved surfaces is called the principal axis
(or)
The line joining the centre of curvatures and the pole.

→ The radius of curvature (R): The distance between the centre of curvature and the optic centre is called the radius of curvature.

→ Centre of curvature (C): The centre of the sphere which contains the part of the curved surface is called the centre of curvature.

→ Focal plane: A plane that is perpendicular to the principal axis at the focus is called the focal plane.

→ Beam: A number of rays combined together are called a beam.

→ Ray: The straight-line path along which the light travels, in a homogeneous medium, is called a ray.

→ Convergent beam: When a group of light rays fall on a convex lens after refraction meets at a point is called a convergent beam.

→ Divergent beam: When a group of light rays fall on a concave lens after refraction move away from a point is called a divergent beam.

→ Parallel beam: When a group of light rays parallel to each other is called a parallel beam.

→ Real image: The image formed on the screen is called a real image.

→ Virtual image: The ¡mage which cannot be formed on the screen is called a virtual image.

→ Aperture: The effective width of a lens through which refraction takes place ¡s called the aperture.

→ Magnifying glass: A glass, which enlarges an object.

→ Biconvex or Double convex lens: A lens that may have two spherical surfaces bulging outwards is called a double convex lens.

→ Biconcave or Double concave Pens: It is bounded by two spherical surfaces curved inward.

→ Lens formula: $$\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}}$$
v = image distance
u = object distance
f = focal length of tens

→ Lens maker’s formula: $$\frac{1}{f}$$ = (n -1)$$\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$$
n = Absolute refractive index
R1 = Radius of curvature of the first surface
R2 = Radius of curvature of the second surface

→ Enlarged image (Magnified image): If the size of the image is greater than that of an object, it is called an enlarged (or) magnified image.

→ Diminished image: If the size of the image is less than that of an object, it Is called a diminished Image.

→ Object distance (u) : Distance between object and lens (optic centre).

→ Image distance (v) : Distance between image and lens (optic centre).

→ Sir David Brewster (11 Dec. 1781 – 10 Feb. 1868):

• Sir David Brewster was a Scottish physicist, mathematician, astronomer, inventor, writer, historian of science.
• Most noted for his contributions to the field of optics.
• He studied the double refraction by compression and discovered the photoelastic effect.
• William Whewell dubbed him the ‘Father of modern experimental optics and ‘The Johannes Kepler of optics’.
• He Is well recognized by the Inventor of Kaleidoscope and stereoscope.