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Flashcards in Physics S3 Deck (31):

Properties of light

-straight lines called rays
-All directions
through different mediums such as gases, liquids, solids (some), and vacuums (space).
-300,000 km per second (3.0 m x 108/s- 8 times around the world in one second).
-behaves like an electromagnetic wave
-Light can be bent (reflection, refraction etc. but not naturally)
-form of energy
-Light makes humans see things (shine on the object and reflect off objects). Invisible when travels until it hit something (we are sensitive to)


Sources of light

Luminous: object that produces light. They have their own source of energy. Ex: sun, glowworm, fireflies
Non-luminous: object that does not produce light and reflects light ex: moon
*Humans see luminous objects because the light enters our eyes directly. Humans see non-luminous objects since the light is reflected off them and into our eyes.



Transparent: materials and objects that can be seen through and allows almost all light to pass.

Light is allowed through with little bending or scattering.

You can read through transparent materials.
Ex: clear glass, clear plastic, clear water



Translucent: materials and objects that allow some light to pass through.
Light rays are scattered and cause you to not have a clear vision on the other side of the object.
You cannot read through translucent material (very difficult)
ex: wax paper, frosted glass, fog



Opaque: materials and objects that do not allow light to pass through and is impossible to see through the object.
Ex: wall, aluminum foil, textbook, orange



Luminescence: the emission of light by a material or an object that has not been heated (or does not require heat and combines substances for light)ie: fluorescence, phosphorescence, Chemiluminescence, bioluminescence.
Ex: sun, candle



-light bulbs

Incandescence: emission of light from a very hot object. Light emitted from a material because of the high temperature of the material and it glows white hot. Ex: sparks, candle, hot metal

Lightbulbs: very inefficient for light as 95% of the energy is lost as heat (old light bulbs) making light a by-product.
How it works: produces light by heating up a metal wire called a filament at a high temperature until it glows (current passes through the filament causing it to heat up and the atoms to become excited.) When it reaches white hot, the light is visible in the visible spectrum.
-uses heat energy and converts it to light energy



Bioluminescence: production of light from living organisms ie: fireflies, fish, glowworm. Light that is produced by a biochemical reaction in a living organism. Chemical reactions in the living cell produce the light. Common in marine organisms.



Phosphorescence: light form phosphorescence - the process of emitting light for some time after receiving energy from another source
Phosphorescence- light that is emitted due to exposure of the source to ultraviolet light, and that continues to be emitted for some time in absence of the ultraviolet light. Very similar to fluorescence however the phosphorescent material is able to retain the energy longer (minutes/hours). Therefore they glow longer after they absorbed the ultraviolet light.
Ex: glow in the dark



Fluorescence- ie: common light bulbs, x-ray, fingerprint powder/spray. Coated with powdery substance of phosphor. The light that is emitted during exposure of the source to ultraviolet light.



Chemiluminescence: emission of light as a result of a chemical reaction and does not produce a lot of heat ie: burning magnesium, fireworks, glow stick. Light that is produced by a chemical reaction without a rise in temperature.


Light scatters in all direction is called

Diffuse reflection: when rays of light hit a rough surface (uneven) and cause the light to reflect in many different directions. This is how we see illuminated objects.


Light reflects as one beam on a smooth surface is called

Specular/regular reflection: when rays of light hit a smooth surface and cause light to reflect following the law that the angle of incidence is equal to the angle of reflection


concave characteristics between focal length and vertex of mirror

• S: Larger than object
• A: Upright
• L: Behind mirror
• T: Virtual image


concave characteristics Object between focal point and centre of curvature: between 5cm and 10 cm

• S: larger than object
• A: Inverted
• L: In front of mirror
• T: real image


concave characteristics Object beyond the centre of curvature: past 10 cm

• S: Smaller than object
• A: Inverted
• L: in front of mirror
• T: Real image


concave characteristics Object at centre of curvature:

• Directly inverted of object
• Same Size


Convex image characteristics

Always the same characteristics
• Smaller than object
• Upright (right side up compared to object)
• Behind mirror
• Virtual image


Where to place object....

Where to place object to have an identical image:
Plane: always same size
Concave: when the object is placed at C or when it is right on the surface of the mirror
Convex: when the object is right on the surface of the mirror

Upright image:
Plane: Always upright image (compared to object)
Concave: when object is placed between F and the mirror (in front of focal point)
Convex: Always upright image (compared to object)

Real image:
Plane: only virtual image
Concave: when object is placed beyond F/greater distance than focal length
Convex: only virtual image


Reflection definition

A ray of light that hits a reflective surface will reflect at the same angle it hits the surface
angle of incidence = angle of reflection

Reflection: the change in direction of a light ray when it bounces off a surface


Refraction definition

the bending of light as it passes THROUGh two different mediums. Speeds of the medium are different.
-distorted image because of refraction
-different speeds and change direction (because of different mediums)


What causes light from hot objects (incandescence) to glow?

made up of several colors mixed colour called WHITE LIGHT/hot


Mirror equation and when to use

1/f = 1/do +1/di

use for focal length, object and image distance


Magnification equation and when to use

m= hi/ho = -di/do

use for magnification factor, object and image height with object and image distance


Parallel incident rays hit the surface and....
(where does it reflect)

reflect through focal point


incident rays that pass through focal point reflect.... Where

reflect off mirror and parallel to principal axis.


If magnification of an image is smaller than 1...

the image will be smaller
Ex: if hi=2
2/3= less than 1 (image is smaller than object)


If magnification of an image is greater than 1...

the image will be larger


Practical uses of a plane mirror

Bathroom mirror, rearview mirror


Practical uses of concave mirror

• Makeup mirrors
• Reflector telescopes
• Solar energy farm (focus light)
• Flashlights and head lights
• Solar cookers


Practical uses of convex mirror

• Security and safety (found in shops) →images are upright and smaller and therefore cover more area
• Decorating (make room seem larger)