- A concave mirror has an inward-curved reflecting surface, while a convex mirror has an outward-curved reflecting surface.
- Important parts of a spherical mirror: Pole (P), Centre of Curvature (C), Principal Axis, and Principal Focus (F).
- For spherical mirrors, the relation is R = 2f, where R is the radius of curvature and f is the focal length.
- In concave mirrors, parallel rays converge at the focus; in convex mirrors, they appear to diverge from the focus behind the mirror.
Definitions [33]
What is light? Define it.
Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.
Define focal length.
The distance between the pole and the principal focus is called the focal length (f) of a spherical mirror.
Define the term Pole.
Pole is the centre of the reflecting surface, in this case, a spherical mirror.
Define the term Aperture.
Aperture is the distance between the extreme points on the periphery of the mirror.
Define the term Centre of curvature.
Centre of curvature is the centre of the imaginary sphere to which the mirror belongs.
Define the term Principle focus.
Principal focus of a spherical mirror is a point on the principal axis of the mirror, where all the rays travelling parallel to the principal axis and close to it after reflection from the mirror, converge to or appear to diverge from.
Define the following term:
spherical mirror
“A mirror which is made from a part of a hollow sphere is called Spherical Mirror.
Define the following term:
convex mirror
“A mirror made by silvering the inner surface such that reflection takes place from the bulging surface” is called Convex Mirror.
The Centre of curvature is towards the silvered surface.
Define the following term:
concave mirror
“A mirror made by silvering the outer or the bulging surface such that the reflection takes place from the concave surface.” Centre of curvature is towards the reflecting surface.
Define the following term in relation to concave mirror.
Pole
Pole “is the mid-point of the mirror”.
Define the following term in relation to concave mirror.
Center of curvature
The centre of a hollow sphere of which the mirror forms a part is called the centre of curvature.
Define the following term in relation to concave mirror.
Principal axis
An imaginary line passing through the pole and the centre of curvature of a spherical mirror is called principal axis.
Define the following term in relation to concave mirror.
Principal focus
It is a point on the principal axis, where a beam of light, parallel to the principal axis, after reflection actually meet.
Define the following term in relation to concave mirror.
Radius of curvature
The linear distance between the pole and the center of curvature is called the radius of curvature.
Define the following term in relation to concave mirror.
Focal length
The linear distance between the pole and the principal focus is called focal length.
Define the term Focus of a concave mirror.
The focus of a concave mirror is a point on the principal axis of the mirror, where all the rays travelling parallel to the principal axis and close to it after reflection from the mirror converge to that point.
Define the term Normal.
Normal to the surface of a mirror at any point is the straight line at the right angle to the tangent drawn at that point.
Definition: Spherical Mirrors
Mirrors whose reflecting surfaces are spherical are called spherical mirrors.
OR
A spherical mirror is a part of a hollow sphere, whose one side is silvered and coated with red oxide and the other side is the reflecting surface.
Definition: Pole
The centre of the reflecting surface of a spherical mirror is a point called the pole. The pole is usually represented by the letter P.
OR
The central point of the reflecting surface of the mirror is called the 'pole' of the mirror.
Definition: Concave Mirror
A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere, is called a concave mirror.
OR
A concave mirror is one whose reflecting surface is towards the centre of the sphere of which the mirror is a part.
Definition: Convex Mirror
A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror.
OR
A convex mirror is one whose reflecting surface is away from the centre of the sphere of which the mirror is a part.
Definition: Centre of Curvature
The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre. This point is called the centre of curvature of the spherical mirror. It is represented by the letter C.
OR
The centre of the sphere of which the mirror forms a part, is called the ‘centre of curvature' of the mirror.
Definition: Radius of Curvature
The radius of the sphere of which the reflecting surface of a spherical mirror forms a part is called the radius of curvature of the mirror. It is represented by the letter R.
OR
The radius of the sphere of which the mirror forms a part, is called the 'radius of curvature' of the mirror.
Definition: Principal Axis
A straight line passing through the pole and the centre of curvature of a spherical mirror. This line is called the principal axis.
OR
The straight line joining the pole and the centre of curvature of the mirror and extended on both sides is called the 'principal axis' of the mirror.
Define principal focus of the concave mirror.
Principal focus (F): The point on the principal axis of the spherical mirror where the rays of light parallel to the principal axis meet or appear to meet after reflection from the spherical mirror.
Define the principal focus of a concave mirror.
Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.
Definition: Refraction of Light
When travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light.
OR
Light changes its direction when going from one transparent medium to another transparent medium. This is called the refraction of light.
OR
The bending of the light ray from its path in passing from one medium to the other medium is called 'refraction' of light.
Definition: Refracted Light
Refracted light is the part of light enters into the other medium and travels in a straight path but in a direction different from its initial direction and is called the refracted light.
Definition: Refraction
The change in the direction of the path of light when it passes from one transparent medium to another transparent medium is called refraction. The refraction of light is essentially a surface phenomenon.
Definition: Prism
A prism is a transparent medium bounded by five plane surfaces with a triangular cross-section.
Definition: Dispersion
The phenomenon of splitting of white light by a prism into its constituent colours is known as dispersion.
OR
The splitting of light into its component colours is called dispersion.
OR
The process of separation of light into its component colours while passing through a medium is called the dispersion of light.
Define the term dispersion of light.
The phenomenon of the splitting of white light by a prism into its constituent colours is known as dispersion of light.
When a beam of white light or composite light is refracted through any transparent media such as glass or water, it is split into its component colours. This phenomenon is called ‘dispersion of light’.
Definition: Spectrum
On passing white light through a prism, the band of colours seen on a screen is called the spectrum.
or
The band of the coloured components of a light beam is called its spectrum.
Key Points
Key Points: Spherical Mirrors
Key Points: Refraction of Light
- When light strikes the boundary between two transparent media, it undergoes partial reflection and partial refraction.
- A ray passing from a rarer to a denser medium bends towards the normal, while one passing from a denser to a rarer medium bends away from the normal.
- The angles of incidence and refraction are generally unequal, causing light to bend.
- A ray incident normally (i = 0°) passes undeviated, even though its speed changes.
- Refraction occurs due to a change in the speed of light when it passes from one medium to another.
Key Points: Laws of Refraction
- The incident ray, the refracted ray, and the normal all lie in the same plane at the point of incidence.
- For a given pair of media, the ratio sin i/sin r = constant, where i is the angle of incidence and r is the angle of refraction.
Key Points: Dispersion of Light
- Dispersion is the splitting of white light into seven colours (VIBGYOR) when it passes through a prism or similar transparent medium.
- Human eyes can detect light with wavelengths ranging from 400 nm (violet) to 700 nm (red).
- Different colours travel at different speeds in a medium like glass, so each colour has a different refractive index.
- Violet light bends the most, and red light bends the least, as it passes through a prism, producing a spectrum.
- A rainbow is formed due to dispersion, refraction, and internal reflection of sunlight by raindrops acting as tiny prisms.
