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i Can radio waves We have just seen that magnetism and electricity AC)stops.Conversely,when an alternating from base are intimately associated with fields.The more magnetic field cuts across a coil of wire, it induces stations harm me or intense the field,the more lines of force per cen- AC to flow in the wire.That is how an electric my family? timeter(or inch),and the stronger the force on generator works.=The generator stops producing external objects.Also,magnetism and electricity current if the magnetic field collapses. are themselves closely interrelated. A magnetic AThe radio waves or electric force weakens dramatically as the dis- When RF current flows in an antenna,electric from base stations tante from the source of the field increases.A and magnetic fields arise and emanate out into are "nonionizing" and magnet has two poles,North and South.A battery space.The result is a radio wave.Each of the two very weak in areas has two terminals,one positive and one negative. fields has a certain strength or amplitude which frequented by the So does an electric generator. In operation,a DC depends on the power contained in the radio wave. public. At such low One measures strong electrnc field in 1.olts per generator's positive terminal always remains poli- meter (V/m);weaker ones in millivolts per meter levels, there is no tive,and the negative terminal remains negative. (mV/m);and very weak ones in microvolts per evidence that they can This is also true of a battery. But an AC generator's meter (pV/m).One measures strong magnetic cause genetic damage two terminals flip polarity at the ACs frequency. fields in amperes per meter (A/m);weaker ones or any other harm to Electrically charged bodies (such as the hard rub- inmilliamperes per meter(mA/m);and very living tissue. ber comb)can be of one polarity only(positive or weak ones in microamperes negative),but a magnet always has two poles. per meter µA/m). Two magnets will attract each other if their nearest B. ELECTROMAGNETIC FIELDS AND poles are opposite;if alike,they will repel.Two LIVING CELLS electrically charged bodies, if of opposite polarity, The Nineteenth Century physicist James Clerk will attract each other;if alike,they will repel.An Maxwell correctly theorized that light waves and electric field of one polarity will pull an oppositely• heat rays are two forms of electromagnetic radiation electrically charged particle toward the field's that share basic characteristics.3 Each comprises a source;the field will repel a charge of like polarity. pair of time-varyingelecaic and Magnetic fields can exert forces on moving electric magnetic fields at charges and bend the particles'paths —unless the right angles to each other.The pair of fields(and charges are moving parallel to the lines of magnetic the wave they comprise)race outward from their force. source at the speed of light and can travel through empty space.4 The basic difference between radio A coil of wire wrapped around an iron or steel bar waves,visible light,and other forms of electro- will act as an electromagnet if electric current flows magnetic waves is the rate at which their fields in the coil.The resulting electromagnetic field reverse polarity(their frequencies). Infrared(heat) strength depends on the amount of current,the rays have higher frequencies than radio waves,and number of turns in the coil,and the bar's magnetic visible light higher frequencies than infrared rays. characteristics.If direct current flows in the coil, The other main difference is how the various the polarity of the magnetic field is fixed,like that forms of electromagnetic waves affect matter. of a horseshoe magnet or a bar magnet.If AC 1. Atoms,Ions,and Molecules flows in the coil,the magnetic field's polarity switches back and forth in step with the AC itself. Matter consists of atoms.Atoms comprise:electrons, The magnetic field collapses if the current(DC or with a negative electric charge;protons,which carry a positive electric charge;and neutrons, WHAT/S RADIATION? which carry a neutral(that is,no)electric charge. Protons and neutrons make up an atom's nucleus. To most people,radiation is a frightening word. Electrons orbit the nucleus,much as planets orbit However,radiation is simply power emitted from the suns A typical atom has equal numbers of a source in waves or particles.It is not the same as radioactivity.Manyprotons and electrons.The positive balance types of radiation have nothing to do with nuclear physics.Some are the negative ones,and the atom is electrically 1111 not even electromagnetic.Sound is one form of neutral.However, if an electron acquires enough radiation;ripples on a pond are another.Radio energy,it can fly off into space.The atom waves,sunligh4 and the wa,urth emitted by a becomes electrically imbalanced,and displays a fireplace or a radiator are all forms of electro- net positive charge.On the other hand,an atom magnetic radiation. can pick up one or more vagabond electrons and 16