Static Electricity Notes PDF

12.2 What do lightning and a photocopier have in common? The surprising answer is static electricity. Static Electricity ▶▶ static electricity: an Static electricity is an...

12.2 What do lightning and a photocopier have in common? The surprising answer is static electricity. Static Electricity ▶▶ static electricity: an Static electricity is an imbalance of electric charge on the surface of imbalance of electric an object. “Static” means not moving. This form of electricity is called charge at rest on the static because the charges stay in one place until they move suddenly surface of an object from one object to another. The device the girl is touching in Figure 1 is called a van de Graaff generator. It generates static electric charge. The student’s hair in the picture 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 strands repel one another and spread out as far from one another as possible. dig deeper Reading Tip Challenging Beliefs You may read explanations that challenge a belief you hold about something you have experienced. Evaluate what you read carefully. You may learn something that will change what you think about static electricity. Figure 1 When you touch a van de Graaff generator as it is charging, a static charge builds up on your hair. This causes the strands to repel each other and stand on end. Electric Discharge ▶▶ electric discharge: An electric discharge (also known as electrostatic discharge or the rapid transfer of ESD) is the sudden movement of static charge between two objects. electrons from one object When you rub your socks across a carpet, electrons from the carpet to another may move to you. When you then touch a metal doorknob, the electrons can move from you to the doorknob. You feel a shock and you may even see the small spark of the discharge. 464   Chapter 12 Static and Current Electricity NEL  dig deeper Small electric discharges are not harmful to you, but they can be strong enough to damage delicate computer parts such as hard Web Link drives or USB memory sticks. In fact, the microchips and circuitry To learn more about how to prevent electrostatic in smaller consumer electronics can be damaged by much smaller discharge (ESD) and to electric discharges. investigate the spectacular natural phenomena of lightning, Lightning go to Nelson Science A lightning bolt is an example of a natural electric discharge. It is caused by the difference in charge between a cloud and the ground, between two clouds, or between parts of a cloud. What causes this imbalance in charge? The process is not fully understood, but scientists do have a theory. Swirling winds in a storm cloud cause water and ice particles to come in contact and become charged. Positive charges move to the top of the cloud where ice and snow crystals form. Negatively charged water droplets move to the bottom of the cloud (Figure 2). dig deeper Did You Know? Anti-static Packaging The packaging used to ship computers, video games and other electronic devices is specially designed to protect the devices from excess electrons on cloud bottom harmful electrostatic charges. You may have seen these special non-conductive bags made of plastic, but, in an effort to go green, more and more manufacturers are electrical discharge (lightning) switching from oil-based plastics to paper-based packaging. Earth Figure 2 The imbalance of charge between a cloud and the ground results in a brilliant flash of lightning. NEL 12.2 Static Electricity and Discharges   465  dig deeper The ground below the cloud develops a positive charge. When Did You Know? the difference in charge between the cloud and Earth becomes Amber great enough, a path forms between the cloud and the ground. The word electricity comes When the two parts meet, a surge of electrons travels along the from the Greek word path. This produces a giant flash called lightning (Figure 3). The (e-lektron) for amber, a type of fossilized tree sap. Ancient lightning heats the surrounding air, making it expand very rapidly. Greeks observed that if you This causes the sudden, loud sound that we hear as thunder. rubbed materials such as wool or fur against amber, it would attract small objects. Figure 3 A cloud-to-ground lightning strike Uses of Static Electricity 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. There are, however, many practical uses for static electricity. Static-cling Film Figure 4 Vinyl decals use Advertisers use static-cling vinyl film for brightly coloured removable static electricity to cling signs, decals, and stickers like the one shown in Figure 4. The to surfaces. 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. 466   Chapter 12 Static and Current Electricity NEL Photocopiers 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. The positively charged ink, called toner, is attracted to the negative charges in the image. As negatively charged paper moves past the drum, the toner particles are transferred to the paper, recreating the image (Figure 5). (a) areas on the drum (b) (c) hit by the laser become positively charged positive toner negatively charged toner particles particles stick to the negatively negatively charged positively charged areas on the drum charged paper selenium drum laser positively charged toner particles Figure 5 (a) The laser “draws” a negatively charged image on the drum. (b) The drum rolls across the positively charged toner, which sticks to the negatively charged laser “drawing.” (c) The drum rolls across paper with a higher negative charge, and the toner particles “stick” to the paper. 12.2 Wrap Up Static electricity is an imbalance of charge at rest on the surface of an object. An electric discharge is a sudden movement of electrons between two objects with different charges. Lightning is a natural discharge of electrical energy. Static electricity has many real-world applications. Static electric discharges can damage electronic devices. Ontario Science 9 SB Check Your 0-635519-7 Learning 1.FN What causes the unexpected spark when you walk C11-F20b-UDOS9SB 4. (a) What is the theory as to how static charge across a rug and touch a metal doorknob? K/U builds up in a thundercloud? You may wish to CO Creative Freelancers draw a diagram to illustrate your explanation. 2. Why do computer technicians have to make sure they do not carry any (b) Explain what causes the explosive release of Samstatic electric charge? A Laterza energy in a lightning bolt. K/U C 3. Why does someone’s hairPass Second stand on end when Pass 5. How do photocopiers make use of static electric they are touching a charging van de Graaff generator? A forces? K/U Approved 6. Write an advertisement about the advantages of Not Approved static cling signs and decals. C A NEL 12.2 Static Electricity and Discharges   467