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Class :- 10 physics. Light:-Reflection and Refraction Light is a form of electromagnetic radiation that is visible to the human eye. It plays a crucial role in various aspects of life and science. Here are some key points about light:
•Nature of light - 1.“Electromagnetic Spectrum” : Light is part of the electromagnetic spectrum, which includes a range of wavelengths from gamma rays (shorter wavelengths) to radio waves (longer wavelengths). Visible light occupies a small segment of this spectrum, roughly between 400 and 700 nanometers.
- “Wave-Particle Duality”: Light exhibits both wave-like and particle-like properties. This duality is a fundamental concept in quantum mechanics . As a wave, light can exhibit phenomena such as interference and diffraction, while as a particle (often referred to as a photon), it can be quantized and interact with matter.
- Speed of light : In a vacuum, light travels at approximately 299, kilometers per second (or about 186,282 miles per second). This speed is considered a universal constant, denoted as "c".
Reflection of light: - Light can bounce off surfaces, which is the principle behind mirrors and many optical devices. There are two main principles that govern this phenomenon:
1.The law of reflection can be summarized as:
- The angle of incidence (i) is equal to the angle of reflection (r): angle i=angle r 2.Incident ray,reflected ray and normal all lie on the same plane.
Type of mirrors:-
1 .Plane Mirror: A flat mirror that produces virtual, upright images with the
same size as the object but reversed left to right. These are commonly used in daily life. :-Image formation by plane mirror
Characteristics of this image :- .virtual .image appears behind the mirror at the same distance as the object is in front of the mirror .size of the image is equal to the size of the object .laterally inverted (left and right are reversed)
2.Spherical mirror:- :-A spherical mirror is a mirror shaped like a segment of a sphere, with its reflective surface either curving inward or outward. There are two main types:
i).Concave mirror: The reflective surface curves inward, like the inside of a bowl. It converges light rays and is also called a converging mirror. Concave mirrors are used in applications like shaving mirrors, telescopes , and headlights.
ii).Convex mirror: The reflective surface bulges outward. It diverges light
.Rules to obtain image from concave and convex
.Ray parallel to principal axis: After reflection , passes through the focus (concave) or appears to come from the focus (convex)
.Ray passing through focus: After reflection, travels parallel to the principal axis
.Ray passing through center of curvature: Reflects back along the same path.
.Ray incident at the pole: Reflects such that the angle of incidence equals the angle of reflection with respect to the principal axis.
A)Image formation by concave mirror: -
�� Sign Convention for Spherical Mirrors:-
.All measurements are made from the pole (P) of the mirror, with the principal axis as the reference line .The object is always placed on the left of the mirror (i.e., incident light comes from the left) .Distances measured to the right of the pole (along the direction of incident light) are positive; to the left are negative .Distances above the principal axis are positive; below are negative .Object distance(u) is always negative (since the object is on the left) .Focal length (f): Concave mirror: negative (focus is in front, to the left). Convex mirror: positive (focus is behind, to the right).
.Image distance (v):
Real image (in front): negative. Virtual image (behind): positive
.Object height is positive (above axis); image height is
positive if erect (above axis), negative if inverted (below axis)
.Mirror formula:-
The mirror formula relates the object distance
(u), image distance (v), and focal length (f) of a
spherical mirror (concave or convex):
1/f=1/v+1/u
u: Object distance (distance from object to
mirror pole)
v: Image distance (distance from image to
mirror pole)
f: Focal length (distance from focus to mirror
pole)
.magnification:-
Magnification (m) shows how much
larger or smaller the image is compared to the
object:
m=Height of Image (h′)/Height of Object
(h)=−v/u
��What is Refraction: -
refraction. (This is true for angle 0< i < 90o) If i is
the angle of incidence and r is the angle of
refraction, then,
sin i/sinr= constant
This constant value is called the refractive
index of the second mediumwith respect to the
first.
*Refraction through a rectangular glass slab :-
��Refractive index:- The extent of the change in direction that takes placein a given pair of media may be expressed in terms of the refractive index. The value of the refractive index for a given pair of media depends upon the speed of light in the two media.
Consider a ray of light travelling from medium 1 into medium 2, as shown in above fig Let v1be the speed of light in medium 1 and v2 be the speed of light in medium 2. The refractive index of medium 2 with respect to medium 1 is given by the ratio of the speed of light in medium 1 and the speed of light in medium 2. This is usually represented by the symbol n21. This can be expressed in an equation form as
By the same argument, the refractive index of medium with respect to medium 2 is represented as n12.It is given by
��spherical lens :-
A spherical lens is a transparent optical component made of glass or plastic, with at least one surface shaped as part of a sphere.There are two main types of spherical lenses:
.Convex lens (converging lens): Thicker in the middle, thinner at the edges; causes parallel light rays to
converge to a point. Types of convex or converging lens
Uses of Convex Lens
- Convex lens are used in microscopes and magnifying glasses.
- Convex lens are used as a camera lens in cameras.
- Convex lens is used in the correction of hypermetropia.
.Concave lens (diverging lens): Thinner in the middle,
thicker at the edges; causes parallel light rays to spread out (diverge) Types of concave lens:-
A convex / concave lens has two principal foci F1 and F2. F1 is towards left of the lens and from this region, light rays are incident on the lens. F2 is towards right of the lens and in this region, light rays are emergent after refraction.
.Rules to obtain image from concave and conv
.A ray parallel to the principal axis:
Convex lens: Passes through the focus on the other side after refraction.
Concave lens: Appears to diverge from the focus on the same side after refraction
.A ray passing through (or directed towards) the focus:
Convex lens: Emerges parallel to the principal axis after refraction.
Concave lens: Emerges parallel to the principal axis after refraction.
.A ray passing through the optical center:
Both lenses: Emerges without deviation, continuing in a straight line.
*figures of both lens for their rules:-
��Image formation by convex lens:-
(1) Optical centre ‘O’ is taken as origin, all the distances along XX’ axis are measured from ‘O’.
(2) Distance along direction of light is considered positive .
(3) Distance measured opposite to the direction of light is considered negative.
(4) Along YY’, the height of object is always taken above principal axis and it is considered positive. For image, if image is virtual and erect (above principal axis), the height is positive. If image is real and inverted (below principal axis), the height is negative.
Some important points related to lenses
(a) Convex lens
(1) u = always negative.
(2) v = –ve, when object is placed between optical centre (O) and focus (F1). v = +ve, for all other possible cases (real and inverted).
(3) f = +ve, power (P) = +ve.
(b) Concave lens
(1) u = always negative.
(2) v = always –ve (virtual and erect).
(3) f = –ve, power (P) = –ve.
(4) Image always diminished.
*Lens Formula
In a lens, the distance of the object from its optical centre is called the object distance (u). The distance of the image from the optical centre of the lens is called the image distance (v).
The relationship between object distance (u), the image distance (v) and the focal length (f) is given by lens formula which is as given below
*Magnification Formula
