Static Electricity Notes PDF

10.1 STATIC ELECTRICITY I THINK YOU WILL FIND THIS UNIT ELECTRIFYING  Atomic structure and Electric Charge Review, all matter is made up of atoms All atoms are made up of smaller particles called subatomic particles Protons have a positive charge Electrons have a negative cha...

10.1 STATIC ELECTRICITY I THINK YOU WILL FIND THIS UNIT ELECTRIFYING  Atomic structure and Electric Charge Review, all matter is made up of atoms All atoms are made up of smaller particles called subatomic particles Protons have a positive charge Electrons have a negative charge Neutrons have neutral charge  More Review Protons and neutrons are located within the nucleus of an atom. Protons and neutrons are held with very strong attraction It is therefore very difficult to remove protons from the nucleus. electrons however, are able to move from one atom to the next.  Cations and Anions Recall; when an atom gains or loses an electron it is called an ion. An atom that has gained one or more electrons is called an anion. An atom that has lost one or more electrons is called a cation.  Representing Positive, Negative and Neutral Charges All objects are obviously made up of billions and billions of atoms. It is impossible to represent each and every atom within an object with their respective charges. Therefore, when we represent objects, we can represent the overall charge that an object has using positive and negative symbols. “+” represents atoms with positive charges. “-“ represents atoms with negative charges.  Representing Charges on objects (c) from the above diagram we can conclude that the object has an overall neutral charge. We know this because the number of + and - symbols are equal. This is how objects will be presented.  Negative, Neutral and Positive Objects (a) represents an object that has an overall neutral charge. (b) represents an object that has an overall positive charge. (c) represents an object that has an overall negative charge.  How do objects gain an overall positive or an overall negative charge Objects,just as atoms, can become charged when they lose or gain electrons. This happens when two objects come into contact with one another. When this happens electrons will transfer from one object to the other. This will result in one object having more total electrons than negative protons, resulting in an overall charge. While the other object will have less total electrons than protons, resulting in that object having an overall positive charge.  Static Electricity Static; meaning to be stationary When two objects have come into contact with one another, and_________ electrons have been transferred from one object to another each object possesses an overall charge. This overall charge will remain within or on the surface of the object until it has a way to leave. This is known as Static electricity. Static, because the charges are stationary on the surface of an object.  Static Electricity So we have a transfer of electrons from one object to another. We now have two objects with overall positive negative and ____________ charges. The negative charges will build up within and on the surface of an object. These charges need a place to go. However, if the object is an _________ insulator then these electrons can not move. They are held on the surface of the object. The object needs to neutralize itself. Neutralizing means transferring the electrons to a conductor so that they can leave the object.  Static Electricity Electrons need a path in order to move. This path can be a solid path (copper wire, metal spoon), a liquid path ( water), or gaseous path (air). The path however, needs to be a conductor , or electrons can not move  Law of Electric Charges What happens when you rub a balloon against your hair You are transferring electrons from your hair to the balloon. + Therefore your hair will gain an overall ___ charge - And the balloon will gain an overall ___ charge.  Law of Electric Charges Why does this happen? The law of electric charges states; REPEL 1) Like charges will _______each other 2) Opposite charges will ATTRACT _______ each other Side Note: Any charge will attract a neutral charge/object Science fact: Law in science has a very specific meaning, and it is a different meaning than THEORY. Law in science is not changeable. For example the Laws of Gravity and Motion by Isaac Newton. The Law of Electric Charges will ALWAYS hold true. TRANSFERRING ELECTRIC CHARGE Part 1: Charging by contact Science Fact: Over 2500 years ago a Greek philosopher, Thales of Miletus, noticed something unusual when he rubbed a piece of amber with fur. He noticed that after contact the amber attracted feathers and pieces of straw. After this point, scientists have learned that neutral objects can become charged through direct contact.  Two common methods of charging by contact are: 1. CHARGING BY FRICTION 2. CHARGING BY CONDUCTION/CONTACT ⦿ This occurs when two different neutral materials are rubbed together or come in contact (touch) and electric charges are moved from one object to the other ⦿ One material will attract electrons and become negatively charged ⦿ One material will give up electrons and become positively charged Are we expected to know which materials gain/lose electrons? Why do you think some materials attract electrons and some give up electrons? This is because: ❖ some atoms are more strongly attracted to electrons than others ❖ there are two different materials that are used that have different strengths on holding on to their electrons  This is a list of materials in order of increasing tendency to gain electrons. As you move further down the list, the materials increase in their tendency to gain extra electrons. Why do we use this chart? To predict the charge that will be gained when two objects are rubbed together. What will be the charge of a piece of paper after rabbit fur is rubbed on it? The paper will gain electrons from the fur and become negatively charged. The rabbit fur will lose electrons to the paper and become positively charged. How do we draw a transfer of electrons 1. We draw both objects as neutral. Both objects contain the same # of _________ and __________ 2. Using the Electrostatic Table, we then draw the objects with more electrons and less electrons The duster has _______ electrons, while the polthene rod has _______ electrons This occurs when two objects of different amounts of electric charges come in contact and electrons move from one object to the other. Let's assume we have a negatively charged metal object and an uncharged metal sphere (Illustration 2a). We bring the two objects close together. We will see a separation of charge happen in the neutral object as negative electrons are repelled to the right hand side (Illustration 2b). At this time, they are not touching and no charges have been transferred. We allow the two objects to touch (Illustration 2c). Some of the negative charge will transfer over to the uncharged metal object. This happens since the negative charges on the first object are repelling each other... by moving onto the second object they spread away from each other. When the negative object is removed, it will not be as negative as it was (Illustration 2d). Both of the objects have some of the negative charge… how much depends on the size of the objects and the materials they are made of. If they are the same size, made of the same materials, then the charge will be the same on both. Overall the total negative charge remains constant. We started with six negative charges, and we ended up with a total of six. Notice that this also means a negative object causes a negative charge on the other object. What would happen if you used a positive rod at the start to touch the metal sphere? Note: In order for conduction to happen, what types of material do you need 10.2 - 10.3 Electrostatics Objects with an excess electric charge, either positive or negative, can have the excess charge removed by a process called GROUNDING. To ground an object it involves removing the excess charge by transferring electrons between the object and a large neutral object, such as the Earth (the ground) Science Fact: The Earth is considered an infinite source of electrons and protons When a positively charged object is grounded, electrons from the ground travel up to the positively charged object until it is neutral. When a negatively charged object is grounded, electrons travel from the object into the ground until the object is neutral.  Making Money using grade 9 Static electricity knowledge Electrostatic Dusters When used, you gently sweep it across an object (charging by friction) causing a buildup of charge on the duster. The dust is attracted to the electrostatic duster and jumps off the dusty surface into the duster  Charging by induction (Temporary Charge) What happens to the electrons and protons when we bring a charged object close to a neutral object. The electrons in the neutral object will either move towards or away from the charged object (depending on the charge of the charged object).  Make a prediction about what will happen to the electrons/protons in the neutral wall.  When the (-) charged balloon is brought close to the neutral wall The electrons in the wall are repelled by the excess electrons in the balloon. Therefore they will be repelled away from the electrons in the balloon. This leaves the part of the wall closest to the balloon with a temporary (+) charge. The part of the wall further away from the balloon is left with a temporary (-) charge.  An everyday example of charging by induction occurs with the buildup of dust on the screen of a television or computer monitor When a computer monitor or television screen is turned on it begins to build up a charge. When a neutral dust particle comes near the screen, the charge on the screen induces an opposite charge on the near side of the dust particle and a charge, similar to that on the screen, on the far side TURN THIS INTO THIS  Charging by Induction (Permanent Charge) An object can be permanently charged by induction by grounding the object When a negatively charged ebonite rod is brought near a neutral pith ball the electrons in the pith ball are repelled and it becomes temporarily negatively charged on its right side  Charging by induction (permanent charge) Attaching a ground wire to the pith ball conducts the repelled electrons on the right side into the ground. After removing the ground wire, the pith ball remains permanently positively charged.  A Shocking Experience An example of a very large electrical discharge. Caused by INDUCTION.  Building Charges The process of evaporation and condensation of atmospheric water within clouds causes water droplets to collide with dust, ionizing radiation, and each other Negative charges build at the base of a cloud The top of the cloud becomes positively charged  Building Charges Through INDUCTION, a temporary positive charge builds on the ground The negative charges on the base of the cloud repel electrons on the surface of the earth  Strong attraction between the negative cloud and positive ground causes the air to act like a conductor (usually an insulator) This attraction pulls electrons off atoms and molecules in the air  Lightning Strike! The cloud discharges the excess electrons (through the air) into the ground creating a huge current of electricity called “lightning” Transfer of electrons usually occurs over the highest point on the ground Lightning Strike! THUNDER The discharge of electrons causes the surrounding air to quickly expand, creating the sound of thunder  Lightning Rods Lightning Rod: a metal pole (conductor) placed on top of buildings that helps direct the flow of electrons away from the building, through a wire and into the ground. Lightning rods become positively charged (induction). They are the highest point in the area, so provide a pathway for electrons to travel from the cloud to the ground. They prevent fires  Lightning Safety Do not be the tallest object (squat, lie down, etc.) Do not stand on high points or under trees Do not travel in aluminum boats on a lake Do not wear golf shoes with metal cleats Seek Shelter (closed car, grounded buildings)