- 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 [41]
Define Regular reflection.
The phenomenon due to which a parallel beam of light traveling through a certain medium, on striking some polished surface, bounces off from it, as a parallel beam, in some other direction, is called regular reflection.
Define reflection.
The bouncing of light by any smooth or polished surface is called.
Define the term Principle axis.
The principal axis is the straight line passing through the pole and the centre of curvature.
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 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.
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 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.
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 the following terms :
Incident ray, Refracted ray, Angle of incidence, Angle of refraction.
INCIDENT RAY AB: The ray light AB which is in air strikes the glass slab at B.
Or
“A ray of light falling on the surface separating the two media.”
REFRACTED RAY BK: A ray of light which after passing the first medium is in second medium i.e. ray BK.
“A ray of light travelling in other medium in the changed direction.”
ANGLE OF INCIDENCE: “The angle which the incident ray makes with the normal is called angle of incidence.”
i.e. ∠i
ANGLE OF REFRACTION: “The angle which the refracted ray makes with the normal is called angle of refraction.”
i.e. ∠r
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.
Definition: Lens
A lens is a transparent refracting medium bounded by either two spherical surfaces, or one spherical surface and the other surface plane.
OR
A lens is a transparent medium bound by two surfaces.
OR
A lens is a transparent medium (such as glass) bounded by two curved surfaces or one curved and one plane surface.
Definition: Diverging Lens or Concave Lens
A lens which is bent inwards in the middle is a concave lens. Such a lens diverges the light rays incident on it, so it is also called a diverging lens.
OR
This lens is thicker near the centre as compared to the edges. The lens with both surfaces spherical on the inside is called a concave or double concave lens.
OR
The lenses which are thinner in the middle and thicker at the edges, are called 'concave lenses'.
Definition: Principal Focus
Principal focus (F) is the point on the principal axis at which light rays parallel to the principal axis converge after passing through a convex lens.
Definition: Focal Length
The distance between the optical centre and principal focus of a lens is called its focal length.
Definition: Principal Axis
The imaginary line passing through both centres of curvature is called the principal axis of the lens.
OR
The line joining the centres of curvature of the surfaces of the lens is called the 'principal axis' of the lens.
Definition: Converging Lens or Convex Lens
A lens which bulges out in the middle, is a convex lens. A light beam converges on passing through such a lens, so it is also called a converging lens.
OR
The lens which has two spherical surfaces which are puffed up outwards is called a convex or double convex lens.
OR
The lenses which are thicker in the middle and thinner at the edges, are called 'convex lenses'.
Definition: Centre of Curvature
The centres of spheres whose parts form surfaces of the lenses are called centres of curvatures of the lenses.
Definition: Radius of Curvature
The radii (R1 and R2) of the spheres whose parts form surfaces of the lenses are called the radii of curvature of the lens.
Definition: Optical Centre
The point inside a lens on the principal axis, through which light rays pass without changing their path is called the optical centre of a lens.
OR
The point on the principal axis of a lens such that a ray of light directed towards it emerges from the lens in the same direction, without deviation.
Definition: Prism
A prism is a transparent medium bounded by five plane surfaces with a triangular cross-section.
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.
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’.
Key Points
Key Points: Reflection of Light
- Reflection occurs when light bounces off a smooth surface like a mirror, following fixed laws.
- Plane mirrors always form virtual, erect, and same-sized images that are laterally inverted.
- Curved surfaces (like a spoon) act as spherical mirrors, changing the image size and orientation depending on the object's position.
Key Points: Spherical Mirrors
Key Points: Concept of Lenses
- Lenses are widely used in daily life, such as in spectacles, peepholes, magnifiers, and telescopes.
- Light passing through a lens undergoes refraction twice: once on entering and once on exiting the lens.
- The shape of a lens affects the direction of light; convex lenses converge light, while concave lenses diverge it.
- Most lenses have surfaces that are parts of spheres, with common types including biconvex, biconcave, plano-convex, and meniscus lenses.
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.
Concepts [15]
- The propagation of light
- Reflection of Light
- Mirrors
- Plane Mirror
- Lateral Inversion
- Divergence and Convergence of Light
- Spherical Mirrors
- Formation of Image by Reflection: Real and Virtual Image
- Spherical Mirror > Concave Mirror
- Spherical Mirror > Convex Mirror
- Concept of Lenses
- Images Formed by Sperical Lenses
- Colour
- Prism
- Dispersion of Light
