Lesson 5 November 5th, 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 RodsEvery year, millions of damage is done to

property from lighting strikes.

Lightning RodsThis 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 RodsThe 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 MaterialsStatic 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 MaterialsGrounds 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 HomeStatic 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 buildingsSpray carpet with antistatic spray / Remove

carpet from the houseUse a humidifier when the air is too dryUse drier sheets – act as conductors and

reduce friction between clothesRemove clothing from the drier before it is

completely dry.

Making Use of Static ChargesBy using static charges in technology, we are

able to make devices that improve our lives.

Spray PaintingSpray 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 PaintingBy using electrostatics, painting can become

much easierThe 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.

PhotocopyingStep 1A 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

PhotocopyingStep 2The 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 3Plastic 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.

PhotocopyingStep 4A 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.

PhotocopyingStep 5The paper is still charged and may be warm

when it comes out of the photocopier.

Environmental ApplicationsAn 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 ApplicationsBefore 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 ApplicationsThese 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)