# DO YOU HAVE ITanswers 133 - PHYSICS 133 DO YOU HAVE IT...

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PHYSICS 133 DO YOU HAVE IT? ANSWERS Three pieces of wire, (1) & (2) are made of the same material, while (3) is made from a material with twice the resistivity. (a) Which has the greatest resistance? (b) If the same voltage is applied across each, which will pass the greatest current. (a) number 2 has the greatest resistance (b) number 1 will pass the greatest current Why are lightning rods pointed? You must attract lightning; therefore you must establish a large surface charge density, which means a large electric field. This ionizes the air and acts as a source for the return stroke. (recall that in terms of charge density a small area means large charge density) Why is it safe staying inside a car during a thunder (lightning) storm? The car is a conductor, therefore you are inside a conductor and the field inside a conductor is zero. When a light bulb burns out, it usually does it just as you turn it on why? Where does the flash come from? As is gets older the filament becomes smaller in diameter, the resistance increases with temperature, at first there is a low resistance, which means large current, this large current can also break the filament due to the magnetic forces. A flash results from a high electric field (between the supports of filament ) developed in the gas (like lightning) As incandescent light bulbs grow older and are used more they get dimmer, why? As the bulb glows tungsten atoms vaporize from the surface and collect on the inner surface of the glass, as a result the radius of the filament decreases with time, increasing the resistance, which lowers the current. Lower current implies lower power hence

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DO YOU HAVE ITanswers 133 - PHYSICS 133 DO YOU HAVE IT...

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