SNC1D PHYSICS 3/9/2013. THE CHARACTERISTICS OF ELECTRICITY L Static Electricity (P.396, ) Static Electricity. Static Electricity

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1 SNC1D PHYSICS THE CHARACTERISTICS OF ELECTRICITY L (P.396, ) What do lightning and a photocopier have in common? How about that unexpected zap when you reach for a doorknob or your hair mysteriously standing on end after pulling off a wool hat on a winter day? March 9, DPHYS - 1 Objects can become charged when electrons move from one object to another. The electric charge that builds up on the surface of the object is called a static charge or static electricity. The charges are static because they remain very nearly fixed in one location on the surface of the object until they are given a path to escape. March 9, DPHYS - 2 1

2 For example, the girl below is touching a van de Graff generator it generates static electric charge. The student s hair shows what can happen when static electricity builds up on someone touching the generator. Each strand of hair has the same static charge. This makes the strandsof hair repel one another and spread out as far as possible. March 9, DPHYS - 3 The accumulation of even larger numbers of electric charges can lead to some impressive electrical displays lightning for example. The large, bright flashes of lightning are the same as the small electric sparks you may have seen when touching a doorknob or taking off a sweater they are just different in size. March 9, DPHYS - 4 NOTE! If a neutral object obtains extra electrons, the object becomes negatively charged. If a neutral object loses electrons, the object becomes positively charged. STATIC CHARGE or STATIC ELECTRICITY electric charge that builds up on the surface of an object caused by a transfer of electrons charge remains fixed in place (ie static ) March 9, DPHYS - 5 2

3 PRACTICE 1. Why might a plastic rod that contains a large number of electrons not have a static charge? the rod is neutral (#e = #p) March 9, DPHYS - 6 Uses of Most of the time we think of static electricity as an annoyance. It makes our hair look messy and can make our clothes stick together. However, scientists and engineers can use the properties of static charges in many useful ways in a branch of science called electrostatics. Electrostatics is the branch of science that deals with static charges and static electricity. ELECTROSTATICS the study of static electric charges March 9, DPHYS - 7 Uses of PRACTICE 2. Name four applications that use electrostatic principles. March 9, DPHYS - 8 3

4 Uses of Advertisers use static-cling vinyl film for brightly coloured removable signs, decals, and stickers like the one shown. The windows of many homes, office buildings, and cars are covered with filters that screen out sunlight. These screens use static electricity to cling to the window. March 9, DPHYS - 9 Uses of PRACTICE 3. Explain why it is not a good idea to try to put up static-cling decals on a very humid day. humid air = no static charge (water molecules in air remove excess charge) March 9, DPHYS - 10 Uses of Electrostatic paint sprayers use the properties of static charges to more efficiently paint objects. The paint is given a charge as it leaves the nozzle of the sprayer, and the object to be painted is given the opposite charge. The charged paint particles are attracted to the object, which minimizes the amount of wasted paint and ensures that the object receives an even coat of paint. March 9, DPHYS

5 Uses of Electrostatic precipitators use the properties of static charges to clean the air. Before the gas from a factory is released it is sent through pipes that charge the tiny particles of pollutants, called particulates, negatively. The gas then moves through an area that has positively charged plates which attract the negative particles and remove them from the gas. Precipitators use very little electricity and can remove about 99% of the particles in smokestack emissions. March 9, DPHYS - 12 Uses of Photocopiers also use the properties of static charges to work. Photocopiers convert an image captured by a scanner into a laser beam. This beam is projected onto a drum or belt, creating a negatively charged pattern (a). The positively charged ink, called toner, is attracted to the negative charges in the image (b). As negatively charged paper moves past the drum, the toner particles are transferred to the paper (c). The paper than passes through a fuser that melts the toner particles onto the paper. March 9, DPHYS - 13 Uses of USESOF static electricity has many practical applications including: static-cling vinyl film (removable signs, stickers, ) electrostatic sprayer (reduces amount of wasted paint) electrostatic precipitator (cleans the air) photocopier March 9, DPHYS

6 1. Explain how eliminating static electricity would hinder the performance of an electrostatic paint sprayer. no static charge = no attraction (paint would blow by) March 9, DPHYS How can neutral pollutant particles be made attractive to the charged plate in an electrostatic precipitator? give the neutral particles a charge before they enter the precipitator March 9, DPHYS Sometimes, finished photocopied paper will stick to you. Explain why. the paper is still charged from the photocopying process March 9, DPHYS

7 TEXTBOOK P.403 Q.6 P.426 Q.5,6,8,14 March 9, DPHYS