Presentation on theme: "Section 25.1 – Properties of Light pp"— Presentation transcript:
1 Section 25.1 – Properties of Light pp. 604-611 Chapter 25 - LightSection 25.1 – Properties of Lightpp
2 TERMS TO LEARNElectromagnetic (EM) wave– a wave that can travel through space and matter. It consists of changing electric and magnetic fields.Radiation – the emission of energy in the form of EM waves
3 LIGHT Light is an EM wave. Light can travel through space and matter. A field is a region around an object that can exert a force on another object without actually touching it (ex.: a magnet is surrounded by a magnetic field that can pull a paper clip toward it).
5 25.1 Properties of lightLight travels fast over long distances and carries energy and information.Light travels in straight lines, but can be bent by lenses or reflected by mirrors heat and warmth.Light has color and can be bright or dim.
6 25.1 The electromagnetic spectrum Light, like sound and heat, is a form of energy.The visible light we see is part of the electromagnetic spectrum.
7 25.1 Properties of lightYou see book pages because light in the room reflects from the page to your eyes.Your eyes and brain use the information carried by the light to make a mental picture.
8 25.1 Light is produced by atoms Most light is produced by atoms.When you put some energy into the atom, it excites the atom’s electrons.Light is produced when the electron releases this energy.
9 25.1 Incandescent lightMaking light with heat is called incandescence.Atoms in the filament convert electrical energy to heat and then to light.Incandescent bulbs are inefficient, but their waste heat can be useful.
10 25.1 Fluorescent lightTo make light, fluorescent bulbs use high-voltage electricity to energize atoms of gas in the bulb.These atoms release the electrical energy directly as light (not heat), in a process called fluorescence.
11 25.1 Color and energyWhen all the colors of the rainbow are combined, we see light without any color.We call the combination of all colors white light.
12 25.1 Color and energyCompare the hot, blue flame from a gas stove to the orange flame of a match.The light from a gas flame is blue (high energy) and the light from a match is red-orange (low energy).
14 25.1 The speed of lightThe speed at which light travels through air is about 300 million meters per second.The speed of light is so important in physics that it is given its own symbol, a lower case “c”.
15 25.1 Speed of lightThe speed at which electromagnetic waves travel through air is about 300 million meters per second.The speed of light is so fast that when lightning strikes a few miles away, we hear the thunder after we see the lightning.
16 25.1 Wavelength and Frequency of Light Because the wavelength of light is so small, scientists measure it in nanometers.One nanometer (nm) is one billionth of a meter ( m).
18 25.1 What kind of wave is light? A sound wave is a oscillation of air.A water wave is an oscillation of the surface of water.An oscillation of electricity or magnetism creates electromagnetic waves.
19 25.1 Electromagnetic waves If you could shake the magnet up and down 450 trillion times per second, you would make waves of red light with a frequency of about 450 THz.
20 25.1 Electromagnetic spectrum The entire range of electromagnetic waves, including all possible frequencies, is called the electromagnetic spectrum.This spectrum includes visible light and invisible waves:radio wavemicrowavesinfrared lightultraviolet lightX-raysgamma rays
22 RADIO WAVESHave some of the longest wavelengths and lowest frequencies of all the EM wavesAre low energy waves
23 AM VS. FM WAVES Amplitude Modulation (A.M.) Frequency modulation (F.M.)Can travel farther than FMMore information can be encoded than AMCan reflect off the ionospherePasses through the ionosphereHave longer wavelengths than FMHave shorter wavelengths than AM
24 TV AND RADIO WAVESTV uses radio waves that have shorter wavelength and higher frequency than those used by radio stations.Most TV stations are broadcast using A.M. and F.M.F.M. waves carry sound; A.M. waves carry pictures
25 MICROWAVESHave shorter wavelength and higher frequency than radio waves.Carry more energy than radio waves.Microwaves are also used in radar (radio detection and ranging).
26 INFRARED WAVESHave shorter wavelengths and higher frequency than microwaves.Can carry more energy than microwaves and radio waves
27 INFRARED WAVES The Sun is a source of IR waves. Stars, planets, buildings, humans and trees also emit IR waves.
28 IR WAVESThe amount of IR radiation emitted by an object depends on the temperature of the object. Warmer objects give off more IR radiation than cooler ones.Your eyes cannot see IR radiation but there are devices that can detect it (i.e. night vision goggles)
30 UV LIGHT Also produced by the Sun. Has shorter wavelength and higher frequency than visible light.Carries more energy than visible light.
31 EFFECTS OF UV WAVES Positive Effects Negative Effects Used to kill bacteria in foodOverexposure can cause sunburn, skin cancer, eye damageCauses skin cells to produce Vitamin DOverexposure can cause wrinkles and premature aging of the skin
32 X-RAYSHave the shortest wavelengths and highest frequency of all EM waves.X-rays carry a lot of energy and can penetrate many materials.Too much exposure to x—rays can damage or kill living cells
33 GAMMA RAYSCarry large amounts of energy and can penetrate materials very easily.Every day you are exposed to small amounts of gamma rays that do not harm you.Radiologists focus these on tumors to kill cancer cells.A negative effect of gamma radiation is that they kill healthy cells.