CHAPTER CHAPTER 2727

LIGHT & OTHER LIGHT & OTHER ELECTROMAGNETIC ELECTROMAGNETIC

WAVES WAVES

Electromagnetic Waves:Electromagnetic Waves: are transverse waves are transverse waves

produced by the motion produced by the motion of electrically charged of electrically charged particles. particles.

An electromagnetic An electromagnetic wave consists of electric wave consists of electric field and magnetic field field and magnetic field waves at right angles to waves at right angles to each other. each other.

Electromagnetic Waves:Electromagnetic Waves: These waves vary These waves vary

depending on depending on frequency and frequency and wavelength.wavelength.

They don’t need a They don’t need a medium to travel.medium to travel.

Electromagnetic Waves:Electromagnetic Waves: Their speed varies with Their speed varies with

the change in medium. the change in medium. All electromagnetic waves All electromagnetic waves

travel at the same speed travel at the same speed through a vacuum (3 x 10through a vacuum (3 x 1088 m/s). Their wavelength m/s). Their wavelength and frequency are and frequency are different.different.

Electromagnetic Waves:Electromagnetic Waves: They carry energy and They carry energy and

have momentum.have momentum.They have both They have both wave wave

and particle like behavior.and particle like behavior.

RADIO WAVESRADIO WAVES

MICROWAVESMICROWAVES

INFRAREDINFRARED

VISIBLE LIGHTVISIBLE LIGHT

ULTRA VIOLET LIGHTULTRA VIOLET LIGHT

X-RAYSX-RAYS

GAMMA RAYSGAMMA RAYS

FREQUENCYINCREASES

WAVELENGTHDECREASES

ENERGYINCREASES

LIGHTLIGHT Light is composed of Light is composed of

tiny “particles”.tiny “particles”. These particle-like These particle-like

bundles of radiation bundles of radiation are called are called photons.photons.

LIGHTHigher the frequency

of the electromagnetic waves, the greater the energy of the wave.

Light produces interference patterns like water waves.

RADIO WAVESHave low frequency and long wavelengths.They have the lowest photon energy.

RADIO WAVESRadio waves are used to

transmit radio and TV signals.

They are also used in cellular phones and cordless phones.

RADIO WAVESThe process of varying radio waves is called modulation.Voice, light images, computer information, and music can be used for modulation.

OTHER USES OF RADIO WAVES

1.Communications2. Navigation and defense

equipment3.Weather Forecasting4.TV signals5. AM and FM radio signals6. Airport air traffic controllers7. Radar used by police cars

INFRA RED RADIATIONINFRA RED RADIATIONHas a wavelength slightly Has a wavelength slightly

longer than visible light.longer than visible light.Your skin feels warm Your skin feels warm

outside because your outside because your

skin is absorbingskin is absorbing

infrared radiationinfrared radiation

from the sun.from the sun.

A thermogram is produced A thermogram is produced by measuring the infrared by measuring the infrared radiation given off by radiation given off by different parts of the body.different parts of the body.

Tumors are detected by Tumors are detected by thermograms because thermograms because they are warmer than they are warmer than other parts of the body.other parts of the body.

Some security Some security systems are systems are designed to detect designed to detect objects giving off objects giving off infra red radiation infra red radiation and to respond by and to respond by activating an alarm.activating an alarm.

Infrared radiation Infrared radiation are used to warm are used to warm and dry objects.and dry objects.

Infra red lamps in Infra red lamps in

some restaurants some restaurants

keep the food keep the food

warm until served.warm until served.

Infrared images obtained Infrared images obtained from from sensors on sensors on airplanes can yield airplanes can yield important information important information

on the health of crops on the health of crops and help us seeand help us seeforest fires even forest fires even enveloped in an enveloped in an

opaque layer of opaque layer of smoke.smoke.

Increasing WavelengthDecreasing Frequency

VISIBLE LIGHTVISIBLE LIGHT

VISIBLE LIGHTVISIBLE LIGHT

It is the only part of the It is the only part of the electromagnetic electromagnetic spectrum that we can spectrum that we can see.see.

Violet Color has a smaller Violet Color has a smaller wavelength than red wavelength than red color.color.

ULTRA VIOLET RADIATIONULTRA VIOLET RADIATIONThey have higher They have higher

frequency than visible light.frequency than visible light.Exposure to UV radiation Exposure to UV radiation

enables skin cell to enables skin cell to manufacture vitamin D, manufacture vitamin D, which is needed for healthy which is needed for healthy bones and teeth.bones and teeth.

ULTRA VIOLET RADIATIONULTRA VIOLET RADIATION

Ultra violet lamps are Ultra violet lamps are used in hospitals to kill used in hospitals to kill bacteria and viruses, bacteria and viruses, and to sterilize surgical and to sterilize surgical instruments.instruments.

UV rays are used to kill UV rays are used to kill microorganisms in food and on microorganisms in food and on hospital equipment.hospital equipment.

Some minerals like fluorite and Some minerals like fluorite and scheelite become fluorescent scheelite become fluorescent when exposed to UV light. when exposed to UV light. Fluorescence occurs when a Fluorescence occurs when a material absorbs UV radiation material absorbs UV radiation and re-emits visible light.and re-emits visible light.

ULTRA ULTRA VIOLETVIOLET RADIATION RADIATION

EXCESS OF ULTRA VIOLET EXCESS OF ULTRA VIOLET RADIATIONRADIATION

•Lead to sagging, dry skin Lead to sagging, dry skin and even skin cancer. and even skin cancer. Sunscreen contains Sunscreen contains chemicals that absorb chemicals that absorb UV radiation before they UV radiation before they penetrate your skin.penetrate your skin.

OzoneOzone is found in the is found in the Earth’s outer Earth’s outer atmosphere and it atmosphere and it protects us from most protects us from most of the sun’s UV of the sun’s UV radiation. radiation.

Crest

Ozone is produced naturally through photochemical reactions and electric discharge reactions (lightning) in the atmosphere.

Ozone depletionOzone depletion is is caused by chemicals caused by chemicals (CFC) that break down (CFC) that break down ozone. These chemicals ozone. These chemicals are found in hair sprays, are found in hair sprays, refrigerants etc. refrigerants etc.

X-RAYSX-RAYSX-rays have shorter X-rays have shorter

wavelength andwavelength and

higher frequencyhigher frequency

than UV radiation.than UV radiation.They possess enough They possess enough

energy to penetrate energy to penetrate dense objects like skin dense objects like skin and muscles.and muscles.

X-RAYSX-RAYSWhen X-rays hit more When X-rays hit more

dense objects they are dense objects they are absorbed.absorbed.

X-rays are used to scan X-rays are used to scan luggage and packages luggage and packages without opening without opening

them at the them at the

airport.airport.

GAMMA RAYSGAMMA RAYSHave the highest Have the highest

frequency and are the frequency and are the most penetrating.most penetrating.

Gamma rays areGamma rays are

emitted emitted

from the nuclei of from the nuclei of

radioactive atoms.radioactive atoms.

GAMMA RAYSGAMMA RAYS

Earth receives some Earth receives some gamma rays from space.gamma rays from space.

They can be used to kill They can be used to kill cancerous cells.cancerous cells.

GAMMA RAYSGAMMA RAYS

People using gamma People using gamma radiation for treatment radiation for treatment suffer side affects like suffer side affects like nausea, hair loss, and nausea, hair loss, and fatigue because healthy fatigue because healthy cells are also damaged.cells are also damaged.

THINK ABOUT ITTHINK ABOUT IT1.Describe at least two 1.Describe at least two

ways in which ways in which electromagnetic waves electromagnetic waves differ from mechanical differ from mechanical waves.waves.

2.Describe at least one 2.Describe at least one helpful use for each of the helpful use for each of the six main types of six main types of electromagnetic radiation.electromagnetic radiation.