Reflection, refraction, lenses, TIR, colours, dispersion Β· 38 terms
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Electromagnetic radiation detectable by the human eye. Wavelength: 400 nmβ700 nm.
Visible light is a tiny slice of the full electromagnetic spectrum β from violet to red.
An object that produces its own light (e.g. the sun, a light bulb).
An object that does not produce its own light but is visible because it reflects light (e.g. the Moon).
The bouncing of light off a surface.
You see yourself in a mirror because light bounces off the mirror back to your eyes.
1. The incident ray, reflected ray, and normal all lie in the same plane. 2. The angle of incidence equals the angle of reflection.
Both laws must be stated for full marks.
The perpendicular line drawn at the point where light meets a surface.
The normal is your reference line β angles are always measured from the normal, never from the surface.
The ray of light approaching the mirror or surface.
The ray leaving the mirror after reflection.
An image formed by the actual intersection of light rays β can be projected onto a screen.
A cinema projector produces a real image on the screen.
An image formed by the apparent (extrapolated) intersection of light rays β cannot be projected onto a screen.
Your reflection in a flat mirror is virtual β the light doesn't actually come from behind the mirror.
The apparent change in position of an object when viewed from two different positions.
Hold your finger up and look at it with each eye alternately β it seems to jump. That's parallax.
No parallax method is used to find focal length of a concave mirror.
The centre of the sphere from which a curved mirror's surface is a section.
The line joining the optical centre of the mirror to C, passing through the pole.
The point where the principal axis intersects the mirror surface.
The point on the principal axis where parallel rays converge (concave) or appear to diverge from (convex) after reflection. F is halfway between C and P.
f = r/2 where r = radius of curvature
The distance from the pole to the focal point.
The distance from the object to the optical centre (pole or lens centre).
The distance from the image to the optical centre.
Use sign convention: real = positive, virtual = negative for mirrors.
The ratio of image height to object height, or image distance to object distance.
m = v/u. Positive = upright, negative = inverted.
The bending of light as it passes from one medium to another due to a change in speed.
A straw in a glass of water appears bent at the surface β that's refraction.
Light bends towards the normal when entering a denser medium, away when leaving.
1. The incident ray, refracted ray, and normal lie in the same plane. 2. nβsin ΞΈβ = nβsin ΞΈβ (the ratio of sines is constant for a given pair of media).
Both laws must be stated. Know the formula n = sin i / sin r.
The ratio of the sine of the angle of incidence in air to the sine of the angle of refraction in the medium.
A denser material (glass, water) bends light more β higher refractive index.
n = sin i / sin r = c/v (speed of light in vacuum / speed in medium)
The angle of incidence in the denser medium that results in an angle of refraction of 90Β° in the less dense medium.
Think of it as the "tipping point" β any angle larger causes total internal reflection.
sin C = 1/n
When light travelling from a denser to a less dense medium strikes the boundary at an angle greater than the critical angle, and is completely reflected back into the denser medium.
Optical fibres use this β light bounces along inside the glass fibre with no escape.
Two conditions: 1. Light going from denser to less dense medium. 2. Angle > critical angle. Both must be stated.
A thin, transparent material through which light travels by repeated total internal reflection.
Internet data (as light pulses) travels through optic fibres across oceans at near light speed.
The ability of the eye to change the focal length of its lens to focus on objects at different distances.
Your eye muscles squeeze or relax the lens to focus close or far β like adjusting a camera lens.
The reciprocal of the focal length: P = 1/f. Measured in dioptres (D).
Converging lens: positive power. Diverging lens: negative power.
The ability of a lens to converge or diverge light rays. P = 1/f.
A mirage caused by cold, dense air near the ground with warmer air above, making distant objects appear elevated.
A mirage caused by hot air near the ground (less dense) under cooler air above, making the sky appear reflected on the ground β looks like water on a hot road.
A hot road appearing wet is an inferior mirage β light from the sky bends upward through hot air near the tarmac.
An instrument used to examine light spectra and measure the wavelength of light.
Red, green, and blue β the three colours that combine to make white light.
Different from paint primaries! Light primaries: R, G, B.
Colours formed by mixing two primary colours in equal intensity: yellow (R+G), cyan (G+B), magenta (R+B).
A primary and secondary colour that combine to make white light. Blue+Yellow, Green+Magenta, Red+Cyan.
The separation of white light into its component colours (spectrum) when it passes through a prism.
A prism splits white light into a rainbow β different wavelengths refract by different amounts.
Light of a single wavelength (one colour only).
Laser light is monochromatic β all the same wavelength.
The absorption of UV radiation by a material and its re-emission as visible light.
Highlighter pens glow under UV light β they absorb UV and re-emit visible light.
Electromagnetic radiation with wavelength just longer than visible red light, emitted by warm objects.
Night-vision cameras detect IR β warm bodies glow in the dark to the camera.