Static Electricity

D4 Explain the relationship among voltage, current and resistance in a simple series circuit.

What do you know about static electricity? Where have you seen or encountered it?

What is electricity? Electricity is the movement and interactions of electrons What is electrical current? Electrical current is the movement of electrons What is static electricity? Static electricity is caused by stationary electrons

This works just like ions! An object can obtain a positive charge by losing electrons or obtain a negative charge by gaining electrons. This works just like ions! Then the objects obey the forces of attraction and repulsion

Static electricity buildup can be caused by Friction Friction occurs when two objects rub against each other. This causes loosely held electrons to move from the surface of an object.

How can you create static by friction? Brushing your hair with a comb Rubbing a balloon against your hair Rubbing a balloon against a wool sweater.

Static build up can be caused by conduction: Conduction- electrons are transferred from one material to another by direct contact. Example – you touch a door knob and get a shock.

The friction of your feet on the rug builds up a charge that is then transferred to the door knob when you touch it.

Static build up can also occur by: Induction - when charges on an object are rearranged without physical contact.

Static build up can be caused by Induction: First rub a balloon against a wool sweater (friction) to build up a charge. Bring this charge close to the wall (but don’t touch it) causing repulsion of electrons of wall’s surface, leaving positive charges. Now the balloon is attracted to the wall.

Clothes build up static charges in the dryer as the tumble, and hair builds up static charge as you comb or brush it. What can you do about it? Lubricate surfaces with waxy or soapy substance. The thin coating reduces friction reduces e- build up  reducing static charge.

Most metals are good conductors. WHY? Conductors- material through which electric charges move easily. Most metals are good conductors. WHY? The atoms in metals are often bonded by metallic bonds that allow the electrons to freely move amongst all atoms. Gold, Silver, Copper, Aluminum, & Mercury. Also acids & H20

Materials that tightly hold their electrons make good insulators. Insulators- materials through which electric charges can not easily move. Materials that tightly hold their electrons make good insulators. Wood, ceramic, rubber, glass, & plastic

Insulators Conductors

Lightning Wind causes the water molecules and other particles to move against each other in the cloud. This cause static build-up of charges. Positive charges accumulate at the top of clouds and negative at the bottom of clouds. ++++++++++++++ ++++++++++++++ - - - - - - - - - - - - - - - - - - - - - - - -

If the difference in charges is great enough, then lightning occurs within the cloud. Intra-cloud lightning is the most common form of lightning. Inter-cloud lightning occurs between clouds.

The negative area in the bottom of cloud causes an induction effect on objects on the ground. Sometime you will see a “blue” glow where the positive charges are concentrated. “St. Elmo’s Fire”. The discharge of electricity from the cloud to the ground causes the lightning strike.