class 10 physics - chapter 10(light-reflection and refraction) full notes
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Explanation:
Introduction to Light – Reflection & Refraction
Light: Definition
Light is a form of energy that enables us to see things. Light starts from a source and bounces off objects which are perceived by our eyes and our brain processes this signal, which eventually enables us to see.
Nature of Light
Light behaves as a:
ray, e.g. reflection
wave, e.g. interference and diffraction
particle, e.g. photoelectric effect
Laws of Reflection
Light incident on another medium
When light travels from one medium to another medium it either:
gets absorbed (absorption)
bounces back (reflection)
passes through or bends (refraction)
When light is incident on a plane mirror, most of it gets reflected, and some of it gets absorbed in the medium.
CBSE Notes Class 10 Science Chapter 10-1
Characteristics of light
Speed of light c=λ×μ, where λ is its wavelength and μ is its frequency.
Speed of light is a constant which is 2.998×108m/s or approximately 3.0×108m/s.
Reflection of light by other media
A medium that is polished well without any irregularities on its surface will cause regular reflection of light. For example, a plane mirror. But even then some light gets absorbed by the surface.
Laws of Reflection
The incident ray, reflected ray and the normal all lie in the same plane. Angle of incidence = Angle of reflection
[∠i=∠r]
CBSE Notes Class 10 Science Chapter 10-2
Propagation of light
Rectilinear propagation of light: Light travels in a straight line between any two points.
CBSE Notes Class 10 Science Chapter 10-3
Fermat’s Theorem
The principle of least time: Light always takes the quickest path between any two points (which may not be the shortest path).
Rectilinear propagation of light and the law of reflection [∠i=∠r] can be validated by Fermat’s principle of least time.
Plane mirror
Any flat and polished surface that has almost no irregularities on its surface that reflect light is called as a plane mirror.
Principle of Reversibility of light
If the direction of a ray of light is reversed due to reflection off a surface, then it will retrace its path.
CBSE Notes Class 10 Science Chapter 10-5
Spherical Mirrors
Spherical mirror
Consider a hollow sphere with a very smooth and polished inside surface and an outer surface with a coating of mercury so that no light can come out. Then if we cut a thin slice out of the shell, we get a curved mirror, which is called a spherical mirror.
Relationship between focus and radius of curvature
Focal length is half the distance between pole and radius of curvature.
F = R/2
Curved Mirror
A mirror (or any polished, reflective surface) with a curvature is known as a curved mirror.
Important terms related to spherical mirror
Pole (P): The midpoint of a spherical mirror.
Centre of curvature (C): The centre of the sphere that the spherical mirror was a part of.
The radius of curvature (r): The distance between the centre of curvature and the spherical mirror. This radius will intersect the mirror at the pole (P).
Principal Axis: The line passing through the pole and the centre of curvature is the main or principal axis.
Concave Mirror: A spherical mirror with the reflecting surface that bulges inwards.
Convex Mirror: A spherical mirror with the reflecting surface that bulges outwards.
Focus (F): Take a concave mirror. All rays parallel to the principal axis converge at a point between the pole and the centre of curvature. This point is called as the focal point or focus.
Focal length: Distance between pole and focus.
Rules of ray diagram for representation of images formed
A ray passing through the centre of curvature hits the concave spherical mirror and retraces its path.
Rays parallel to the principal axis passes through the focal point or focus.
Image formation by spherical mirrors
For objects at various positions, the image formed can be found using the ray diagrams for the special two rays. The following table is for a concave mirror.
1/v + 1/u = 1/f where ‘u’ is object distance, ‘v’ is the image distance and ‘f’ is the focal length of spherical mirror, which is found by similarity of triangles.
The magnification produced by a spherical mirror is the ratio of the height of the image to the height of the object. It is usually represented as ‘m’.
Position and Size of image formed
Size of image can be found using the magnification formula m = h’/h = – (v/u) If m is -ve it is a real image and if it is +ve it is a virtual image.
Refraction Through a Glass Slab and Refractive Index
Refraction
The shortest path need not be the quickest path. Since light is always in a hurry, it bends when it enters a different medium as it is still following the quickest path. This phenomenon of light bending in a different medium is called refraction.
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