Exploring the Nature of Static Electricity Section 10.1 Exploring the Nature of Static Electricity

Electrical charges are charged particles that exert a force on each other. Some real life examples of these charges include: when charges cause strands of hair to repel each other and be attracted to a balloon Your hair flies up after taking off a sweater or hat When you receive a shock when you touch a doorknob or door handle of a car

Electrically charged particles Remembering from our previous unit on chemistry, we know that an element is a pure substance that cannot be broken down further, and that the elements are made up of tiny particles called atoms. Also, we learned that atoms are made up of three sub-atomic particles: PROTONS which have a positive charge, ELECTRONS which have a negative charge, and, NEUTRONS which have no (neutral) charge. PROTONS and NEUTRONS are found in the nucleus of the atom, while ELECTRONS are found in the orbits.

The Atom Although there are electrically charged particles in the atom, they have the same number of positively and negatively charged particles, making them neutral

Static Charges Sometimes, electrons can move from one object to another. When these electrons move to the surface of another object, a static charge or static electricity is created. These are called “static” because they stay on the surface of an object until they have a path to escape. If an object has more electrons than it has protons, it is negatively charged, and if there are more protons than electrons, than the object is positively charged. The three groups of objects according to charge are: 1. Positive (has lost electrons) 2. Negative (has gained electrons) 3. Neutral (equal numbers of protons and electrons)

Friction and the Movement of Electrons Solid materials become charged by transfer of electrons. This commonly occurs when two objects rub against one another. Friction is the force resisting the relative motion of two surfaces in contact. Friction can remove electrons from one object and move them to another. ONLY ELECTRONS MOVE; THE PROTONS DO NOT MOVE.

Look at the diagram below and in each of the bottom boxes, explain what is happening with the iron rod and the cloth: neutral Gaining negatives Losing negatives Negative positive

Electron affinity Electron affinity refers to an objects tendency to hold onto electrons. Some common items’ electron affinity are as follows: Tend to lose electrons   Tend to gain electrons (+)  human hands (dry)  glass  human hair  nylon  cat fur  silk  cotton  steel  wood  amber  ebonite  plastic wrap  Teflon ( - ) The table above shows how different items will gain or lose electrons, and is referred to as ELECTROSTATIC SERIES_.

Answer questions 2, 3, and 5 on page 398. 2. What does “static” mean in “static electricity? Static means not moving. Static electric charges tend to remain on the surface of insulators (materials that do not allow electric charges to move through them easily).

3. What happens when 2 objects made out of different materials are rubbed together? Different materials have different electron affinities (different abilities to hold their electrons). The object with a stronger electron affinity will take electrons from the object with a weaker electron affinity. The object with the strong affinity becomes negatively charged by gaining electrons. The object with the weaker affinity becomes positively charged by losing electrons.

5. In each of the following pairs, state which one is more likely to give up electrons. Wood or human hair Plastic wrap or steel Cotton or silk _ + _ + _ +

Law of Electric Charges (Laws of Attraction and Repulsion) This is a three part law that is made up of the following statements 1. The Law of Attraction states that particles with opposite charges attract. 2. The Law of Repulsion states that particles with like charges repel. 3. Neutral objects will attract to any charged object (positive or negative).

Coulombs In the 18th century, French physicist Charles-Augustin de Coulomb discovered that when two charged objects are close together, the attraction or repulsion increases, and when the charged objects move further apart, the attraction or repulsion decreases. This attraction or repulsion shows the electric charge. The unit for electric charge is the coulomb (C), and represents 6.24 x 1018 electrons added or removed from a neutral object.

Electrical Insulators and Conductors Conductivity refers to the ability of electrons to move freely in an object. Some materials hold onto electrons and they cannot freely move around within the object. These are called insulators. An object that is an insulator can hold a static charge because static charges remain nearly fixed in place. Materials that can easily pass through them are called conductors. Conduction is the movement or transmission of electrons through a substance. Some materials can move electrons, but not very well. These are called fair conductors.

Some examples of conductors, fair conductors and insulators are: Copper water with dissolved minerals rubber Aluminum moist air wood Iron human body plastic Mercury carbon pure water Other metals soil metal oxides, such as rust

Water as a conductor Dissolved minerals in water makes it conductive. Some safety precautions to consider with water and electricity are: 1.You should not be in a lake during a thunderstorm. If lightning hits water, the electric charges from the lightning will spread through the water and cause serious or fatal injury. 2. You should not use water to try to put out an electrical fire. 3. You should not operate electrical appliances near water or with wet hands.

1 on page 403 Draw a diagram of an atom that has 4 p+, 5 no, and 4 e-. Label each particle with its name and whether it is +, - or neutral Electrons (-) P+= 4 no=5

2 on page 403 What is friction? Friction is the force resisting the relative movement of 2 surfaces in contact. (b) Explain how friction can be used to transfer electrons. Use 2 substances from the triboelectric series in your answer. Friction provides energy to the electrons in a substance. That energy can cause electrons to move. An object with a low electron affinity (like human skin) will tend to lose its electrons and become + charged, while a substance with a high electron affinity (like plastic) will tend to gain those electrons and become – charged.

3 on page 403 Explain why this statement if false: “A neutral object contains no charge.” All objects are made of atoms which contain positive protons and negative electrons. These objects contain charges. The overall object is neutral because the number of protons and electrons are equal.

5 on page 403 Where are static charges held? Static charges are held on the SURFACE of an object.

6 on page 403 Why might a plastic rod that contains a large number of electrons not have a static charge? If there is a balance (equal numbers) between the number of electrons and the number of protons, the charge will not have a static charge – meaning it is not positive or negative. The object will be neutral.

10 on page 403 Do two identical objects become statically charged when you rub them together? Explain why they do or do not. The two objects will not become statically charged because they will have the same electron affinity. Neither will have a stronger hold on their electrons, so neither will lose or gain electrons from the other object. They will remain neutral.

11 on page 403 Pairs Becomes more positively charged Becomes more negatively charged Cotton, steel Cotton, silk Human hair, human hands Teflon, wood Glass, plastic wrap Cotton Steel Silk Cotton Human hands Human hair Wood Teflon Glass Plastic wrap