CHAPTER 27 LIGHT OTHER ELECTROMAGNETIC WAVES Electromagnetic Waves

CHAPTER 27 LIGHT & OTHER ELECTROMAGNETIC WAVES

Electromagnetic Waves: üare transverse waves produced by the motion of electrically charged particles. üAn electromagnetic wave consists of electric field and magnetic field waves at right angles to each other.

Electromagnetic Waves: üThese waves vary depending on frequency and wavelength. üThey don’t need a medium to travel.

Electromagnetic Waves: üTheir speed varies with the change in medium. üAll electromagnetic waves travel at the same speed through a vacuum (3 x 108 m/s). Their wavelength and frequency are different.

Electromagnetic Waves: üThey carry energy and have momentum. üThey have both wave and particle like behavior.

FREQUENCY INCREASES RADIO WAVES MICROWAVES INFRARED WAVELENGTH DECREASES VISIBLE LIGHT ULTRA VIOLET LIGHT ENERGY X-RAYS INCREASES GAMMA RAYS

LIGHT ü Light is composed of tiny “particles”. ü These particle-like bundles of radiation are called photons.

LIGHT ü Higher the frequency of the electromagnetic waves, the greater the energy of the wave. ü Light produces interference patterns like water waves.

RADIO WAVES üHave low frequency and long wavelengths. üThey have the lowest photon energy.

RADIO WAVES üRadio waves are used to transmit radio and TV signals. üThey are also used in cellular phones and cordless phones.

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

OTHER USES OF RADIO WAVES 1. Communications 2. Navigation and defense equipment 3. Weather Forecasting 4. TV signals 5. AM and FM radio signals 6. Airport air traffic controllers 7. Radar used by police cars

INFRA RED RADIATION üHas a wavelength slightly longer than visible light. üYour skin feels warm outside because your skin is absorbing infrared radiation from the sun.

§ A thermogram is produced by measuring the infrared radiation given off by different parts of the body. § Tumors are detected by thermograms because they are warmer than other parts of the body.

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

§ Infrared radiation are used to warm and dry objects. § Infra red lamps in some restaurants keep the food warm until served.

§ Infrared images obtained from sensors on airplanes can yield important information on the health of crops and help us see forest fires even enveloped in an opaque layer of smoke.

Increasing Wavelength Decreasing Frequency

VISIBLE LIGHT

VISIBLE LIGHT It is the only part of the electromagnetic spectrum that we can see. Violet Color has a smaller wavelength than red color.

ULTRA VIOLET RADIATION üThey have higher frequency than visible light. üExposure to UV radiation enables skin cell to manufacture vitamin D, which is needed for healthy bones and teeth.

ULTRA VIOLET RADIATION üUltra violet lamps are used in hospitals to kill bacteria and viruses, and to sterilize surgical instruments.

ULTRA VIOLET RADIATION üUV rays are used to kill microorganisms in food and on hospital equipment. üSome minerals like fluorite and scheelite become fluorescent when exposed to UV light. Fluorescence occurs when a material absorbs UV radiation and re-emits visible light.

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

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

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

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

X-RAYS üX-rays have shorter wavelength and higher frequency than UV radiation. üThey possess enough energy to penetrate dense objects like skin and muscles.

X-RAYS üWhen X-rays hit more dense objects they are absorbed. üX-rays are used to scan luggage and packages without opening them at the airport.

GAMMA RAYS üHave the highest frequency and are the most penetrating. üGamma rays are emitted from the nuclei of radioactive atoms.

GAMMA RAYS üEarth receives some gamma rays from space. üThey can be used to kill cancerous cells.

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

THINK ABOUT IT 1. Describe at least two ways in which electromagnetic waves differ from mechanical waves. 2. Describe at least one helpful use for each of the six main types of electromagnetic radiation.