Unit 3 Static Electricity

Unit 3 Static Electricity Objectives: Discuss the nature of static electricity. Use an electroscope to determine unknown charges. Discuss lightning protection. List nuisance charges of static electricity. List useful charges of static electricity.

Unit 3 Static Electricity 3-1 Static charges can cause a painful shock!

Unit 3 Static Electricity Charges Static charges can be a nuisance, or dangerous, or beneficial. Electric shocks from walking on carpet can be annoying. Electrostatic discharge can ruin sensitive electronic components. Copy machines and sandpaper rely on the application of static electricity.

Unit 3 Static Electricity 3-2 Grains of sand receive a charge to help them stand apart when making sandpaper.

Unit 3 Static Electricity Charges Electronic air filters called precipitators use static charges to attract small particles in the air and trap them in the filter. The word static means not moving. Electrostatic charges build up on insulators. A static charge can be positive or negative.

Unit 3 Static Electricity 3-3 Electronic air cleaner or precipitator

Unit 3 Static Electricity 3-4 Producing a static charge.

Unit 3 Static Electricity Electroscope The electroscope was an early device that indicated the polarity of a charged object. The electroscope uses a metal ball to transfer a known polarity charge to thin metal leaves. When an object with an unknown charge is brought near the metal ball, the action of the leaves reveals the nature of the object’s charge.

Unit 3 Static Electricity 3-5 Electroscope.

Unit 3 Static Electricity 3-6 Charging the electroscope with a negative static charge.

Unit 3 Static Electricity 3-7 The action of the leaves reveals the polarity of the pen’s charge.

Unit 3 Static Electricity Lightning The best example of static electricity in nature is lightning. The movement of water droplets in a thundercloud generates a static charge. Lightning occurs when the positive and negative areas have the potential difference to overcome the air’s resistance.

Unit 3 Static Electricity 3-9 The typical thundercloud contains areas both positively and negatively charged.

Unit 3 Static Electricity Lightning Protection Lightning rods are used to help protect objects from lightning. Lightning rods provide a safe path to channel the electric discharge. A lightning arrestor is also used for protection.

Unit 3 Static Electricity 3-10 Lightning travels from negative to positive areas.

Unit 3 Static Electricity 3-11 A lightning rod provides an easy path to ground.

Unit 3 Static Electricity 3-12 Useful static charges are often used in spray painting.

Unit 3 Static Electricity 3-13 The drum of a copy machine is coated with selenium.

Unit 3 Static Electricity 3-14 The drum receives a positive charge.

Unit 3 Static Electricity 3-15 The image is transferred to the selenium drum.

Unit 3 Static Electricity 3-16 Negatively charged powder is applied to the positively charged drum.

Unit 3 Static Electricity 3-17 The negatively charged powder is attracted to the positively charged paper.

Unit 3 Static Electricity Review: The word static means not moving. An object is positively charged by removing electrons. An object is negatively charged by adding electrons. An electroscope is a device used to determine the polarity of an object.

Unit 3 Static Electricity Review: Static charges accumulate on insulator materials. Lightning is an example of a natural static charge.