9.2 Charging by Friction, Conduction and Induction (Pg. 279-281)

Name: ______Block: ______Science 9 – Ch. 9 Static Electricity 9.2 Charging by Friction, Conduction and Induction (pg. 279-281) What is static electricity?  It is an electric charge that stays in one place for a length of time.  Any object that can detect a static charge is called an electroscope.  There are 3 types of charge o Positive ( ______) – more protons than electrons o Negative (______) – more electrons than protons o Neutral (______) – equal numbers of protons & electrons

We define electrification as the process by which matter lose or gain electric charges. There are three main types of electrification: ______, ______, and ______.

Charging by Friction: The only reason that we are able to use electricity in our modern world is that it is possible to separate positive and negative charges from each other The frictional charging process results in a transfer of electrons between two insulating objects which are ______. In this process, an object takes ______(it becomes ______) from the other object (it becomes ______).

Example 1: clothes in the dryer (large amounts of electric charge build up), When a rubber balloon is rubbed with animal fur or hair, the rubber balloon gains electrons and the animal fur loses electrons. A transfer of electrons takes place. When you rub the balloon, it becomes negatively charged, it has taken some of the electrons from the animal fur and left the fur positively charged.

Remember the conservation of charge. No charges have been created or destroyed, just moved around.

Charging by Conduction: Conduction just means that the two objects will come into actual physical contact with each other (this is why it is sometimes called “charging by contact”).

. ______: when objects______and an electric charge is transferred from one object to another. The neutral object will have the ______charge as the charged object because the charges are being “shared”. . Let's assume we have a negatively charged metal object and an uncharged metal sphere (Figure 2a). . We bring the two objects close together. We will see a separation of charge happen in the neutral . We allow the two objects to touch (Figure 2c). ______. When the negative object is removed, it will not be as negative as it was

Charging by Induction: . Is it possible to charge a conductor without coming into direct contact with it?  ______: when objects ______and an electric charge is transferred from one object to another. The neutral object will have the ______charge as the charged object.  For example: when your computer or TV screen is turned on, it begins to build a charge. When a neutral particle of dust comes near the screen, it will become attracted and stick to the screen. Electroscopes: How can you tell if an object has a charge, especially if you’re doing research in the 1700’s? Very early on physicists started using electroscopes to measure very small charges on objects. An electroscope is made up of a couple of very thin metal leaves that hang down near to each other. They are connected to a metal rod that extends upwards, and ends in a knob on the end.

Imagine what happens to the metal leaves if a charged object is brought nearby…

HW: pg. 281: CYU Q 4, 5, 7, 8, 9, 10 9.3 Insulators and Conductors (pg. 282-284)

Materials can be divided in ______or ______(insulators) of electricity.

Insulator: substances that ______allow electrons to move freely from one atom to another Example: Glass, cotton, plastic are examples of insulators (resistant to electron motion).

Conductor: substances that ______allow electrons to move freely from one atom to another Example: Metals are good conductors of electricity because the outermost electrons in the atoms are loosely bound to the nucleus. When salts are dissolved in water their ions (cations and anions) can move freely through the solution.

Grounding:  Makes the object ______by removing any excess static charge

 You can ground the object by connecting to ______with a conductor.

1. What does it mean to say an object is grounded? ______

2. How do you ground an electroscope? ______

3. What is the purpose of an electroscope? ______

4. Explain why a person is safe from lightning inside a car that has a metal body.

______HW: pg. 284: CYU Q 3, 4, 6, 7, 9, 10 next day ( Quiz 9.1-9.3) 1. When two materials are rubbed together, electrons are transferred from one material to the other (diagram should show one object losing electrons and the other object gaining electrons). The electrostatic series can be used to predict which material will become negative and which will become positive.

2.Charging by conduction is where a charged object is brought into contact with a neutral object and the charge is transferred to the neutral object.

3.Charging by induction is where a charged material is brought near another material and causes the electrons in the material to move or shift slightly.

4.Charging by contact always produces the same charge since the charge is shared.

5.A negatively charged object has an excess of electrons. When it touches the pith ball, some of the excess electrons are transferred by conduction to the pith ball. Since both the object and the pith ball are now negatively charged, they repel each other.

6.Charging by conduction involves direct contact and produces the same charge on the object charged. An example of charging by conduction is touching a metal sphere with a charged vinyl strip. Charging by induction does not involve direct contact and produces an opposite charge on the object. An example of charging by induction is bringing a charged vinyl strip close to a metal sphere.

7.No, a positively charged object cannot negatively charge another object by conduction since the charge is shared. Induction can produce a temporary separation of charge in an object. If the object is then separated into two parts, then the charges can be made permanent.

8.Friction between your feet and the sheets produces equal, but opposite, charges. Skin and the material of the sheets must be apart from each other in the electrostatic series. As the charge builds up, there is enough charge to produce a discharge flash between your feet and the sheets. Pulling tape from a roll acts similarly to friction and causes a buildup of static charge. When the charge is large enough, there is a spark.

9. To determine the static charge on a sock, take an object with a known charge on it (such as a negatively charged pith ball), and see if it attracts or repels the sock. Like charges repel and opposite charges attract. A negative pith ball on a thread would attract a positively charged sock and repel a negatively charged sock.

10. (a) Charged rod is brought near a metal sphere. (b)Metal sphere is grounded by a finger.