Reflection, Refraction, Human Eye, Electricity & Magnetism – Lecture Summary

Vocabulary flashcards covering key terms and definitions on reflection & refraction of light, mirrors and lenses, human eye structure and defects, dispersion and atmospheric optics, basic electricity, circuit elements, heating effect, magnetism, electromagnets, and household electrical safety.

Reflection of Light

The bouncing back of light when it strikes a polished surface such as a mirror.

Law of Reflection (First)

Angle of incidence equals angle of reflection (i = r).

Law of Reflection (Second)

Incident ray, reflected ray, and the normal all lie in the same plane.

Angle of Incidence

The angle between the incident ray and the normal.

Angle of Reflection

The angle between the reflected ray and the normal.

Normal (Optics)

An imaginary line perpendicular to the surface at the point of incidence.

Concave Mirror

A spherical mirror with the reflecting surface curved inward; converges light.

Convex Mirror

A spherical mirror with the reflecting surface curved outward; diverges light.

Principal Axis (Mirror)

The straight line passing through the pole and centre of curvature of a mirror.

Pole (Mirror)

Mid-point of the reflecting surface of a spherical mirror.

Centre of Curvature (Mirror)

Centre of the sphere of which the mirror is a part.

Radius of Curvature

Distance between the pole and the centre of curvature (PC).

Principal Focus (Mirror)

Point on the principal axis where parallel rays converge (concave) or appear to diverge (convex).

Focal Length (Mirror)

Distance between the pole and principal focus (f).

Mirror Formula

1/f = 1/v + 1/u (relates object distance u, image distance v and focal length f).

Magnification (Mirror)

m = -v/u = hi / ho (ratio of image height to object height).

Sign Convention (Mirrors)

Distances measured from the pole: left of mirror negative, right positive; heights upward positive, downward negative.

Convex Mirror Image Nature

Always virtual, erect and diminished.

Concave Mirror Image at Infinity

Real, inverted, highly diminished at focus.

Concave Mirror Image between F and C

Real, inverted and enlarged beyond C.

Convex Lens

Lens thicker in the middle; converging lens.

Concave Lens

Lens thinner in the middle; diverging lens.

Optical Centre (Lens)

Central point within a lens where a ray passes undeviated.

Principal Focus (Lens)

Point on principal axis where rays parallel to axis converge (convex) or appear to diverge (concave).

Focal Length (Lens)

Distance between optical centre (O) and principal focus (F).

Lens Formula

1/f = 1/v – 1/u (sign convention similar to mirrors).

Magnification (Lens)

m = v/u = hi / ho.

Power of a Lens

P = 1/f (in metres); measured in dioptres (D).

Positive Lens Power

Indicates a converging (convex) lens.

Negative Lens Power

Indicates a diverging (concave) lens.

Absolute Refractive Index

Ratio of speed of light in vacuum to speed in the medium (n = c/v).

Snell's Law

n₁ sin i = n₂ sin r (relates incidence and refraction angles for two media).

Refraction of Light

Bending of light when it travels from one medium to another.

Rarer to Denser Bending

Ray bends toward the normal.

Denser to Rarer Bending

Ray bends away from the normal.

Dispersion

Splitting of white light into its constituent colours by a prism.

Spectrum

Ordered band of seven colours obtained after dispersion.

Angle of Deviation (Prism)

Angle between the incident ray’s initial direction and emergent ray direction.

Colour Bending Least

Red bends least in a prism.

Colour Bending Most

Violet bends most in a prism.

Human Eyeball

Approx. spherical structure of ~2–3 cm diameter housing optical components.

Cornea

Transparent, bulging membrane providing most of the eye’s refraction.

Iris

Coloured diaphragm that controls pupil size.

Pupil

Aperture that regulates amount of light entering the eye.

Crystalline Lens

Flexible convex lens inside the eye that fine-tunes focus.

Ciliary Muscles

Muscles that adjust focal length by changing lens curvature.

Retina

Light-sensitive screen where real, inverted images are formed.

Rods (Eye)

Photoreceptor cells for low light intensity vision.

Cones (Eye)

Photoreceptor cells responsible for colour & bright-light vision.

Optic Nerve

Carries electrical signals from retina to the brain.

Aqueous Humour

Water-like fluid between cornea and lens providing nutrients.

Vitreous Humour

Gel between lens and retina helping maintain eyeball shape.

Power of Accommodation

Ability of eye lens to adjust focal length to see objects at different distances.

Near Point

Minimum distance (~25 cm for a normal eye) for clear vision.

Far Point

Farthest point a normal eye can see clearly (infinity).

Myopia

Near-sightedness; distant objects blur; corrected with concave lens.

Hypermetropia

Far-sightedness; nearby objects blur; corrected with convex lens.

Presbyopia

Age-related loss of accommodation; often corrected with bifocal lenses.

Cataract

Clouding of the eye’s lens causing vision loss; treated by surgery.

Prism Experiment (Newton)

Demonstrated dispersion by splitting and recombining white light.

Advance Sunrise & Delayed Sunset

Atmospheric refraction makes Sun visible about 2 min before actual rise and after actual set.

Twinkling of Stars

Apparent brightness fluctuation due to atmospheric refraction in varying density layers.

Blue Colour of Sky

Result of preferential scattering of shorter-wavelength blue light by air molecules (Rayleigh scattering).

Reddening of Sun

Longer path at sunrise/sunset scatters shorter wavelengths leaving red/orange hues.

Tyndall Effect

Scattering of light by colloidal particles making beam path visible.

Electric Charge

Property of matter causing electrical effects; two types: positive and negative; SI unit coulomb (C).

Electron Charge

Smallest independent charge; e = 1.6 × 10⁻¹⁹ C (negative).

Electric Current

Rate of flow of charge (I = Q/t); SI unit ampere (A).

Conventional Current Direction

From positive to negative potential (opposite to electron flow).

Potential Difference

Work done per unit charge moving between two points; unit volt (V).

Resistance

Opposition to current flow in a conductor; unit ohm (Ω).

Resistivity

Material property (ρ) governing resistance: R = ρ l/A; unit Ω·m.

Ohm’s Law

V ∝ I (at constant temperature); V = IR.

Series Resistance

Total R_s = R₁ + R₂ + R₃; same current flows, voltage divides.

Parallel Resistance

1/R_p = 1/R₁ + 1/R₂ + 1/R₃; same voltage, current divides.

Electric Power

Rate of electrical energy consumption; P = VI = I²R = V²/R; unit watt (W).

Electrical Energy Unit

Kilowatt-hour (kWh); 1 kWh = 3.6 × 10⁶ J.

Joule’s Law of Heating

Heat produced H = I²Rt in a resistor.

Heating Effect Applications

Used in electric bulbs, toasters, heaters; requires high resistivity materials.

Electric Fuse

Safety device with low-melting-point alloy wire that melts on excess current, breaking circuit.

Fuse Rating

Maximum current a fuse can safely carry (e.g., 5 A, 15 A).

Overloading

Excess current in household wiring causing overheating; prevented by fuses/MCBs.

Short Circuit

Direct connection of live and neutral, leading to very high current.

Earthing

Connecting metal body of appliances to earth wire to prevent electric shock.

Magnet

Object that attracts iron, cobalt, nickel; has north and south poles.

Magnetic Field

Region around a magnet or current-carrying conductor where magnetic force is experienced.

Magnetic Field Lines

Imaginary lines representing magnetic field direction and strength; never intersect.

Uniform Magnetic Field

Field with parallel, equally spaced lines indicating constant strength & direction.

Right-Hand Thumb Rule

Thumb in current direction; curled fingers show magnetic field around straight conductor.

Solenoid

Coil of many circular turns producing uniform magnetic field similar to bar magnet.

Electromagnet

Strong temporary magnet formed by solenoid wound on soft iron core; strength depends on turns and current.

Fleming’s Left-Hand Rule

Forefinger = field, centre finger = current, thumb = motion/force on conductor.

Force on Current-Carrying Conductor

Magnitude F ∝ B I l sin θ; depends on magnetic field, current, length, and angle.

Alternating Current (AC)

Current changing direction periodically; obtained from power stations; voltage transformable.

Direct Current (DC)

Current flowing in one direction; supplied by cells/batteries.

Domestic Wiring Parallel Connection

Appliances connected in parallel to receive same voltage and independent operation.

Live Wire

Carries 220 V AC supply in household circuits.

Neutral Wire

Returns current to source; approximately at earth potential.

Earth Wire

Safety wire connected to ground to protect against electric shock.

Magnetic Field Strength Around Wire

Increases with current, decreases with distance from wire.