Lesson 5 November 5 th, 2010

Lightning Lightning storm safety begins by watching for towering cloud formations that signal developing storms. Lightning can strike up to 15 km from where it is raining.

As a guideline, if you can hear thunder, you are in striking distance and should look for shelter. Safe shelter includes a large buildings, cars, school buses, etc. Avoid high places, tall objects and any objects that conduct electricity. Lightning strikes cause about six deaths per year in Canada and result in injuries to about 60 people.

Lightning Rods Every year, millions of damage is done to property from lighting strikes.

Lightning Rods This damage can be avoided by the use of lightning rods. A metal pole with a wire attached to it that runs down to the ground.

Lightning Rods The main purpose of a lightning rod is to provide a point removed from the main structure of a building where a stream of electrically charged particles is more likely to form. If lightning hits the lightning rod, the flow of electrically charged particles is directed harmlessly down to the ground so the building is not damaged.

Grounding Static Charges on Vehicles Friction occurs when two surfaces rub against each other. Automobiles and airplanes build up charge through friction between the vehicle’s outer surface and the air. A simple way to prevent static build-up on a car is to use a ground strap

Grounding Static Charges on Vehicles Airplanes have needle-like projections called static wicks located in various places on the wings and plane body. The force of repulsion between charges becomes so strong around a point that charges will disperse into the air from the point.

Static Charges and Flammable Materials Static charge build-up is especially dangerous when using flammable materials Fuel moving through fuel lines creates a build-up of static charges which could lead to a spark which could ignite the fuel

Static Charges and Flammable Materials Grounds are used on the nozzle and fuel trucks to avoid sparks. When gassing up a car, always touch your door before touching the touching the nozzle.

Static Charges and Flammable Materials

Electronic equipment and static charges Sparks caused by static charges can damage sensitive electronic equipment. People who work with this type of equipment take special care to reduce the risk of sparks by wearing grounds themselves or placing them on the equipment.

Reducing Static Charges in the Home Static is built up when two insulators are rubbed together. Dry air also causes more charges to build up because dry air acts as an insulator. Moist air is a fair conductor

Ways to reduce static charges from buildings Spray carpet with antistatic spray / Remove carpet from the house Use a humidifier when the air is too dry Use drier sheets – act as conductors and reduce friction between clothes Remove clothing from the drier before it is completely dry.

Making Use of Static Charges By using static charges in technology, we are able to make devices that improve our lives. Spray Painting Spray painting can result of overspray (paint that does not land on the intended surface) Paint that does not land on the area intended Paint bounces off the surface being painted

Spray Painting By using electrostatics, painting can become much easier The paint coming out of the nozzle gains a negative charge through friction. The surface of the car has been given a positive charge.

Unlike charges attract, so the paint is attracted to the surface of the car. There is less waste due to bounce and overspray, and the finish is smooth and uniform.

Photocopying Step 1 A positive charge is created on the drum. The drum is an insulator, but it becomes a conductor when exposed to light. For this reason, it is called a photoconductor

Photocopying Step 2 The image on the paper to be photocopied is projected onto the drum. Where the light hits the drum, the area becomes conductive, loses its charge, and becomes neutral. The dark areas remain positively charged.

Step 3 Plastic particles and toner (ink) are sprayed onto the drum. As the particles come out of the sprayer, they get charged negatively. The negatively charged toner sticks to the positively charged areas on the drum, creating a copy of the original paper.

Photocopying Step 4 A sheet of paper is pressed against the drum and heated. Heat and pressure cause the toner to fuse to the paper. In some photocopiers, the paper is also charged to help the toner stick to it.

Photocopying Step 5 The paper is still charged and may be warm when it comes out of the photocopier.

Environmental Applications An electrostatic precipitator makes use of the laws of static charges to clean air. The gas discharged from a factory can contain tiny particles of pollutants, called particulate matter.

Environmental Applications Before the gas is released, it is sent through pipes that charge the particulate matter negatively. The gas then moves through an area that has positively charged plates. The positive plates attract the negative particles and remove them from the gas.

Environmental Applications These collector plates are cleaned periodically to keep the system running efficiently. Industrial plants that produce cement, steel, lumber, and petrochemicals use similar techniques to remove dust from the air. Similar processes are also used in mining, and recycling.

Questions 1. Why is it not a good idea to take shelter under a tree in a thunderstorm? I (1) 2. How is charge build-up reduced on airplanes? I (1) 3. Why is a ground strap a necessary safety feature when transferring fuel? I (1) 4. Sometimes, finished photocopied paper will stick to you. Explain why. I (1) 5. Why does Earth not become charged when many people in the world ground objects? I (1)