Chapter 19 Adriana Ramirez Laura Marrero Maria Rivera Gabriel Rúllan Physical Science 8 th Grade T. Imarlys Cajigas

o All matter is made of particles called atoms. o Atoms are made of smaller particles: Protons Neutrons Electrons o Protons and electrons have the property of electric charge, neutrons do not.

o There are two types of electric charge: Positive (+) Negative (-) o Protons in the nucleus of an atom have positive charge. o Electrons in the electron cloud have negative charge. Positive Negative

o Oppositely charged particles attract each other. Protons and electrons attract each other. Two protons, and two electrons repel each other. o Electrically neutral atoms have equal amounts of positive and negative charge. o When an atom gains one or more electrons (ion), it becomes negatively charged. If an atom loses one or more electrons, it becomes positively charged.

o Large objects can gain or lose electrons, just like atoms. o When this happens, the positive and negative charge on the objects become unbalanced. Static charge: unbalanced positive or negative electric charge on an object o Like atoms, objects that gain electrons are said to be negatively charged, while objects that lose electrons are said to be positively charged.

o Electric field: region surrounding a charged object o An electric field applies electric force to charged objects, even if the objects are not touching. o The electric force applied by an object’s electric field will either attract or repel other charged objects.

o The strength of the electric force between two charged objects depends on two variables. Total amount of charge on both objects Distance between objects o Ex. When you brush your hair, electrons move from the brush to your hair. The brush is positively charged. The hair is negatively charged. They attract each other. o If you continue to brush your hair, more electrons transfer from the brush to your hair; increasing the amount of charge.

o The strength of an electric field increases as distance between the two objects decreases. o The strength of an electric field decreases when the distance between the charged objects increases.

o Electric insulator: material in which electrons cannot easily move Glass Rubber Wood Plastic o Electric conductor: material in which electrons can easily move Metals (copper & aluminum)

o When objects made of different materials touch, electrons tend to collect on the object that holds electrons more tightly. o Both insulators and conductors can be charged by contact. Only type of transfer that charges insulators. + _ +_ - _ - +_ + _ - _ _ - Before Rubbing + _ +_ - _ - +_ + _ - _ _ - Before Rubbing +_+_++_-_+ - +_- + _-_-_ _-_+- Before Rubbing +_+_++_-_+ - +_- + _-_-_ _-_+- Before Rubbing +_+_- +_-_+ - +_- +- _-_-_+ - _ _ _+- After Rubbing +_+_- +_-_+ - +_- +- _-_-_+ - _ _ _+- After Rubbing _ + _ + + _ - After Rubbing _ + _ + + _ - After Rubbing

o Is a process by which one object causes two other objects that are conductors to become charged without touching them. o Polarized: when electrons concentrate at one end of an object

o In conduction, objects with unequal charges touch, electrons flow from the object with a greater concentration of negative charge to the object with a lower concentration of negative charge. o The flow of electrons continues until the concentration on charge of both objects is equal. o Occurs between two conductors.

o An electric discharge is the process an of an unbalanced electric charge becoming balanced. o Lightning Rods and Grounding o An electric discharge can occur slowly, such as when your hair loses its negative charge and is no longer attracted to a brush. Or, an electric discharge can occur as quickly as a flash. For example, lightning is a powerful electric discharge that occurs in an instant. o Providing a path for electric charges to flow safely into the ground is called grounding.

o Scientist say the formation of thunder is related to the electric charges that separate within the storm clouds. The large amounts of ice, hail, and partially frozen water droplets that thunder storms create also have to do with the formation of lightning.

Within a storm cloud, warm air rises past falling cold air. The cold air is filled with hail, ice, and partially frozen water droplets that pick up electrons from the rising air. The negatively charged cloud polarizes Earth’s surface repelling negative charges in the ground. Thus, the surface of the ground becomes positively charged. When the bottom of the cloud accumulates enough negative charge, the attraction of the positively charged ground causes electrons in the cloud begin moving forward the ground. As electrons approach the ground, positive charges quickly flow upward, making an electric connection between the cloud and the ground. You see this electric discharge as lightning. Accumulation of charge does not only occur between clouds and the ground. Charges also separate within or between storm clouds, causing cloud-to-cloud lightning.

o The transferring of electric charges allows you to power the electrical devices you use every day. Conduction of electric charges occur when you turn on a light in your house, induction is used for wireless charging devices like electrical toothbrushes. o An electric current is the movement of electrically charged particles. o An electric current flows in a closed path to and from a source of electric energy, this closed path is called an electric circuit. o Charge transfer by contact happens when lightning strikes. In fact, a flash of lightning and a TV are similar in the fact that they both transform the energy of moving electrons to light, sound, and thermal energy. The movement of electrons in a lightning strike lasts very little, but in the TV the electrons continue moving until you turn the TV off.

o How Electric Charges Flow in a Circuit: out of the wire back into the source. o The Unit For Electric Current Electric current is measured approximately as the number of electrons that flow past a point every second. There are so many tiny electrons in a circuit that you can’t count them one at a time. A coulomb is a very large number about 6 quintillion. The SI unit for electric current is the ampere. Its symbol is A. One ampere of current equals one coulomb of electrons flowing in a circuit every second. The electric current through a 120-W lightbulb is about 1 A. A typical hair dryer uses a current of about 10 A, or 60,000,000,000,000,000,000 electrons per second.

o Electric resistance is a measure of how hard it is for an electric current to flow in a material. o The unit of electric resistance is the ohm, which is symbolized by the Ω. o Electric resistance of Conductors and Insulators Conductors are materials that allow electrons to move easily. A good conductor has a low electric resistance. Most wires are made of copper because it’s a good conductor. Insulators though, have a high electric resistance, such as wood, and prevents electrons from flowing in a circuit. o Resistance- Length and Thickness A material’s electric resistance also depends on the material’s length and thickness. The thicker the copper wire is the least resistance the wire has. Yet, increasing its length would also increase its resistance.

o A circuit with high voltage source can transform more electric energy to other energy forms than a circuit with a low voltage source. o Different amounts of energy transform in different parts of a circuit. o By measuring the voltage in a portion of a circuit you can find how much energy in that portion of a circuit is transformed. Voltage: The amount of energy the source uses to move one coulomb of electrons through the circuit.

o This law can be written in the following equation: o V: Symbol for Voltage measured in Volts(V) o I: Symbol for electric current measured in amperes (A). o (R) is the symbol for the electric resistance measured in ohms (Ω). Voltage (V)= current(I) x resistance (R) V=IR V I R Quick Tutorial

o This figure shows two light bulbs each connected to a circuit. Both are connected one after another in a single loop. o Even though the currents are the same the light bulbs are not. One has a greater resistance than the other. o You can determine which has more resistance with a voltmeter and with an understanding of Ohm’s law. o This law states that with o equal current, the voltage o is greater across the o device with greater o resistance, and so the o light bolt with greater o resistance has greater o voltage.

o Computers, lamps, TVs all these have electric circuits. o The common parts of most electric circuits are a source of electrical energy, electrical devices that can transform the electrical energy, and conductors, such as wires, that connect the other components. Electricity Source

o An energy source such as a battery produces an electric current in a circuit. o Some electrical devices are assigned to change that electric energy into kinetic energy-the energy of motion. o Like an electric fan, it transforms electric energy into the kinetic energy of the moving air particles that keep you cool.

o A battery is commonly used as an energy source for a circuit. o When chemicals in a battery react, the electrons move to the negative side, or the negative terminal of the battery. o If the batteries are in a closed circuit, then the electrons move from a negative to a positive terminal. If this reaction keeps occurring, the electric current continues.

o All parts of a circuit change the forms of energy, for example, they can change from : electrical to sound electrical to light electrical to kinetic o Also, all the parts of a circuit can change the electricity into waste, or thermal energy. o Devices like CFLs give off less waste energy because they transport the energy through a gas, instead of wire filaments. This way, less energy is changed into thermal energy.

o Since an electric curret only flows through a closed circuit, the energy source must be connected to the circuit with a conducting material. o Metal wires are used frequently because they are good conductors. They also have low electric resistance, therefore they produce less waste energy.

o There are two types of circuits: Series Circuits electric circuit with only one path for the electric current to flow Parallel Circuits electric circuit that has more than one path for an electric current to flow

o In a series circuit, if a wire loop is broken or opened, the devices in the circuit will turn off. o The amount of devices in the circuit will affect the current. If you have more devices, there is more resistance in the current. As stated in Ohm’s Law, if the resistance increases and the voltage is still the same, the current is lower.

o In a parallel circuit, if you open a branch or a path from the circuit, the current continues. o The devices in a parallel circuit have their individual “branches” used to connect with the source of energy. o One circuit does not affect another, but it does affect the overall current, which increases when more paths are added.

o Many of the energy we use comes from power plants and is transported to us through electrical wires. o The electricity, when it has reached your house, goes through a main wire. o Then, it passes through a meter that measures the amount of electricity used in your house. o After passing the meter, the main wire reaches the main panel, where the main wire divides into smaller wires and to the different areas of your house.

o In your house, if there are too much paths connected to the parallel circuit, there could be a fire or other incidents caused by too much current. o Some devices, like fuses and circuit breakers can be used to prevent these damages. Fuses and circuit breakers open another circuit, so that the excess current can move on to the other circuit. A fuse works by melting, using the thermal energy given off from the current. A circuit breaker is a switch that forms a new circuit so that the current becomes balanced.

o GFCI can be used to prevent the current in a parallel circuit to become too high. o Are used in places close to water. o If the GFCI detects that some electricity is being lost and is not being used in the device, it opens another circuit. This can help avoid electric shocks and death.

o Electric currents have the tendency to move towards the ground through the object, or even person, with least resistance. This way, an electric current can pass through your body to reach ground. This is known as an electric shock. 1 A 0.01A Painful Deadly 0.1A

o To avoid being damaged by an electrical shock, you should do the following: not use electrical devices next to water not use objects with broken cords do not plug many electronic devices in the same outlet try to avoid objects you are using to come in contact with electricity avoid contact with things or persons with a “downed” wire do not play close to electrical stations or substations

o While working on this project, we learned many things, like what is a static charge, and what is Ohm’s Law. We also learned about electric safety, and which electric shocks can be painful and deadly. We reviewed terms like parallel circuits, series circuits, conductors and insulators. Overall, electricity is a “tool” that can give us many benefits, as well as it can cause damage, if not used correctly.

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