0 science light reflection and refraction notes
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Answer:
reflection: angle of incidence equal to angle of reflection. Refraction:incident ray can pass there by as refracted ray
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.
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]
Propagation of light
Rectilinear propagation of light: Light travels in a straight line between any two points.
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.
Characteristics of images
Images can be real or virtual, erect or inverted, magnified or diminished. A real image is formed by the actual convergence of light rays. A virtual image is the apparent convergence of diverging light rays.
If an image formed is upside down then it is called inverted or else it is an erect image. If the image formed is bigger than the object, then it is called magnified. If the image formed is smaller than the object, then it is diminished.
Image formation by a plane mirror
The image formed by a plane mirror is always virtual and erect.
Object and image are equidistant from the 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.
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.