Chapter 11 - Nelson Science 10

Medium

Any physical substance through which energy can be transferred

Radiation

A method of energy transfer that does not require a medium; the energy travels at the speed of light.

Electromagnetic Waves

A wave that has both electric and magnetic parts, does not require a medium, and travels at the speed of light.

Electromagnetic Spectrum

The classification of electromagnetic waves by energy

Applications of **radio waves**

• AM/FM Radio

• TV Signals

• Cellphone communication

• Radars

• Astronomy (e.g. discovery of pulsars)

Applications of **microwaves**

• Telecommunications

• Microwave ovens

• Astronomy (e.g. background radiation from the Big Bang)

Applications of **infrared light**

• Remote controls (e.g. DVD players and game controllers)

• Lasers

• Heat detection

• Keeps food warm (e.g. fast-food restaurants)

• Astronomy (e.g. discovering chemical composition of celestial bodies)

• Physical therapy

Applications of **visible light**

• Human vision

• Theatre/convert lighting

• Rainbows

• Visible lasers

• Astronomy (e.g. optical telescopes, discovering chemical composition of celestial bodies)

Applications of **ultraviolet light**

• Causes skin to tan and sunburn

• Increases risk of developing skin cancer

• Stimulates production of vitamin D

• Kills bacteria in food and water (sterilization)

• “Black” lights

• Ultraviolet lasers

• Astronomy (e.g. discovering chemical composition of celestial bodies)

Applications of **x-rays**

• Medical imaging (e.g. teeth and broken bones)

• Security equipment (e.g. scanning luggage at airports)

• Cancer treatment

• Astronomy (e.g. study of binary star systems, black holes, centres of galaxies)

Applications of **gamma rays**

• Cancer treatment

• Astronomy (e.g. study of nuclear processes in the universe)

• Product of some nuclear decay

Luminous

Produces its own light (e.g. sun, candles)

Non-luminous

Does not produce its own light (e.g. pencils, textbooks)

As an object gets hotter, the colours of light produced change from…

from red, to orange, to yellow, to white, and then to bluish-white.

Incandescence

Production of light as a result of high temperature

How do incandescent light bulbs work?

• Has a thin wire filament, usually made of tungsten, that glows as electricity passes through it

• Filament becomes so hot that it gives off visible light

• Also emits infrared light that you feel as heat radiating from the bulb

What must be removed for incandescent light bulbs to work?

• For an incandescent bulb to work, all the air from the bulb must be removed and replaced with non-reactive gas. (O2 can cause filament to burst into flames)

• Without O2 present, the filament eventually disintegrates and breaks

Why are incandescent light bulbs inefficient?

Only 5-10% of electricity is actually converted into visible light, the rest is converted into infrared light (heat)

Electric Discharge

The process of producing light by passing an electric current through a gas (e.g. neon lights)

How was electric discharge light production discovered?

* Heinrich Geissler created a powerful vacuum pump to remove most of the air from a closed tube.
* The remaining air glowed when an electric current was passed through it.
* Colour of glow depended on the type of gas that was inside the tube

Phosphorescence

The process of producing light by the absorption of ultraviolet light resulting in the emission of visible light over an extended period of time. (e.g. glow-in-the-dark)

How do phosphors work?

• Phosphors absorb light energy, primarily ultraviolet light.

• It keeps some of the energy and releases visible light of lower energy

Fluorescence

The immediate emission of visible light as a result of the absorption of ultraviolet light

* E.g. detergent to make clothes brighter

How do fluorescent lights work?

* Fluorescent lights make use of both electric discharge and fluorescence
* Tube is filled with low-pressure mercury vapour and the inner surface is coated with a fluorescent material.
* When turned on, the electric current causes the mercury atoms to emit ultraviolet light.
* UV light then strikes the fluorescent inner surface of the tube, resulting in the production of visible light.

Pros and cons of fluorescent light

• 4-5x more efficient than incandescent bulbs (less heat + less electricity)

• Downside: contain mercury and should not be disposed of with regular household waste (hazardous)

Chemiluminescence

The direct production of light as the result of a chemical reaction with little or no heat produced

How do chemiluminescent light sticks work?

* Light sticks operate by causing 2 chemicals to mix
* One chemical is in a narrow, small glass vial in the middle of the stick, the second is in the main body of the stick.
* Bending causes the small glass vial to break, allowing the chemicals to mix and produce visible light.

Why are chemiluminescent lights good?

• Inexpensive to manufacture

• Very popular for use in camping, law enforcement, military personnel, entertainment venues, emergency situations, underwater divers

Bioluminescence

The production of light in living organisms as the result of a chemical reaction with little or no heat produced

Glow in a firefly is caused by…

A chemical reaction between oxygen and luciferin (enzyme)

Triboluminescence

Production of light from fiction as a result of scratching, crushing, or rubbing certain crystals

Full name for LED

Light-Emitting Diodes

LEDs

Light produced as a result of an electric current flowing in semiconductors

Semiconductors

A material that allows an electric current to flow in only one direction

Why are LED lights good?

Compared to incandescent bulbs, LEDs do not require a filament, do not produce as much heat as a by-product, and is more energy efficient

Light ray

A line on a diagram representing the direction and path that light is travelling

Geometric optics

The use of light rays to determine how light behaves when it strikes objects

Incident light

Light emitted from a source that strikes an object

Transparent

When a material transmits all or almost all incident lights; objects can be clearly seen through the material (e.g. clear glass)

Translucent

When a material transmits some incident light but absorbs or reflects the rest; objects are not clearly seen through the material (e.g. frosted glass)

Opaque

When a material does not transmit any incident light; all incident light is either absorbed or reflected; objects behind the material cannot be seen at all (e.g. cardboard)

Image

Reproduction of an object through the use of light

Mirror

Any polished surface reflecting an image

Reflection

The bouncing back of light from a surface

Describe the layers of mirrors

Mirrors consist of 2 parts: front part is a sheet of glass and the back part is a thin layer of reflective silver or aluminum.

* The symbol used in physics to represent a mirror refers only to the reflective thin film

Incident ray

The incoming ray that strikes a surface

Reflected ray

The ray that bounces off a reflective surface

Normal

The perpendicular line to a mirror surface

Perpendicular

At right angles

Angle of Incidence

The angle between the incident ray and the normal

Angle of Reflection

The angle between the reflected ray and the normal

The 2 laws of reflection

1. Angle of incidence = angle of reflection

2. The incident ray, the reflected ray, and the normal all lie in the same plane

Specular reflection

• Reflection of light off a smooth surface

• A series of parallel incident rays that strike a smooth surface will have identical angles of incidence (meaning that angles of reflection will all be identical and reflected rays will all be parallel to each other)

Diffuse reflection

Reflection of light off an irregular or dull surface

* Reflected rays would be scattered in many different directions

Virtual image

An image formed by light coming from an apparent light source; light is not arriving at or coming from the actual image location.

(Appears behind the mirror)

Lateral inversion

The orientation of an image in a plane mirror that is backwards and in reverse order

What does the acronym SALT mean?

1. Size of image (compared to the object: same size, smaller, or larger)

2. Attitude of image (which way the image is oriented compared to the object: upright or inverted)

3. Location of image

4. Type of image (real or virtual). A real image is an image formed where light is actually arriving at the same location.

Describe an image in a plane mirror using SALT

An image in a plane mirror is always the same size as the object (size), upright by laterally inverted (attitude), behind the mirror and the same distance behind as the object is in front (location), and virtual (type).