Untitled Quiz

• Light travels in a straight line in rectilinear propagation.
• Speed of light (c) = 3 x 10⁸ m/s

Reflection

• Bouncing back of light from a shiny surface.
• Examples include mirrors or water.
• The incident ray, reflected ray, and normal all lie in the same plane.
• The angle of incidence (i) is equal to the angle of reflection (r).

Plane Mirror

• A smooth and polished surface reflecting light uniformly.
• Images are always virtual and erect.
• Images are the same size as the object.
• The image appears as far behind the mirror as the object is in front.
• Images are laterally inverted.

Spherical Mirror

• Reflecting surface is part of a hollow sphere of glass.
• Concave mirror: reflecting surface is curved inwards.
• Convex mirror: reflecting surface is curved outwards.
• Pole (P): the center point of the reflecting surface.
• Center of Curvature (C): the center of the sphere that forms the mirror's surface.
• Radius of Curvature (R): the radius of the sphere, R=2f.
• Principal Axis: the straight line through the pole and centerof curvature.
• Principal Focus (F): the point where parallel rays converge or diverge after reflection.
• Focal Length (f): the distance between the pole and principal focus.
• Aperture: the diameter of the reflecting surface.

Ray Diagrams

• A ray parallel to principal axis passes through the focus after reflection.
• A ray through the center of curvature retraces the path after reflection.
• A ray through the principal focus becomes parallel to the principal axis after reflection.
• A ray incident at the pole reflects back at the same angle with the principal axis.

Sign Conventions for Spherical Mirrors

• The object is usually placed to the left of the mirror.
• Distances are measured from the pole of the mirror.
• Distances along the incident ray (+X-axis) are positive, against it (-X-axis) : negative.
• Distances above the principal axis are positive, and below are negative.
• Object distance is always +ve
• Focal length of concave mirror is -ve
• Focal length of convex mirror is +ve

Important Formulas

• Magnification (m) = Height of image (h') / Height of object (h)
• m = -v/u
• h' = positive for virtual images
• h' = negative for real images
• m = negative for real images
• m = positive for virtual images

Object and Image Positions/Sizes for Concave Mirrors

• Object at infinity: image at focus F, highly diminished/point-sized, real and inverted.
• Object beyond C: image between F and C, diminished, real and inverted.
• Object at C: image at C, same size, real and inverted.
• Object between C & F: image beyond C, enlarged, real and inverted.
• Object at F: image at infinity, highly enlarged, real and inverted.
• Object between P and F: image behind the mirror, enlarged, virtual and erect.

Object and Image Positions/Sizes for Convex Mirrors

• Object at infinity: image at focus F, highly diminished/point-sized, virtual and erect.
• Object between infinity and P: image between P and F, diminished, virtual and erect.

Uses of Concave Mirrors

• Torches, searchlights, vehicle headlights.
• Shaving mirrors.
• Dentist's mirrors.
• Solar furnaces.

Uses of Convex Mirrors

• Rear-view mirrors in vehicles.
• Preferred in vehicles due to erect, diminished images.
• Offer wider field of view due to outward curve.
• Allow drivers to view a larger area compared to plane mirrors.

Refraction of Light

• Phenomenon of change in light's direction when passing from one transparent medium to another.

Laws of Refraction

• The incident ray, refracted ray, and normal all lie in the same plane.
• Snell's Law: sin i / sin r = constant

Refractive Index

• nm = Speed of light in air (c) / Speed of light in medium (v)
• Measurement of how much a light ray bends.

Lenses

• Transparent material bound by two surfaces, one or both spherical.
• Convex lens: thicker in the middle, converges light.
• Concave lens: thicker at edges, diverges light.
• Center of Curvature (C1, C2): center of sphere forming lens surface.
• Principal Axis: straight line through both curvature centers.
• Optical Center (O): central point where light passes undeviated.
• Aperture: effective diameter of the lens.
• Principal Focus (F1, F2): point where parallel rays converge (convex) or diverge (concave).
• Focal Length (f): distance between principal focus and optical center.

Ray Diagrams for Lenses

• A ray of light from the object, parallel to the principal axis
• A ray of light passing through a principal focus
• A ray of light passing through the optical centre of a lens
• Convex lens
• Object positions
• Concave lens
• Object positions

Lens Formula

• 1/f = 1/v - 1/u
• m = Height of image(h')/ Height of object(h) = v/u

Power of Lens

• Ability of a lens to converge or diverge light after refraction determines power.
• Defined as the reciprocal of focal length.
• SI unit is Dioptre (D).
• 1 dioptre is power of lens whose focal length is 1 metre.
• Power of a convex lens = positive
• Power of concave lens = negative.

Uses of Concave Lens

• spy holes in the doors
• glasses
• some telescopes

Uses of Convex Lens

• overhead projector
• camera
• focus sunlight
• simple telescope
• projector microscope
• magnifying glasses