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Science 9 Electricity Notes Name:_____________Block:_____ Ch_9_Review: Static Electricity: Review of Chapter 9 (Pages 274-299) The buildup of electrical charge as the result of some types of materials being rubbed together. Ex: getting a shock by touching something after walking on a rug, your hair sticking up after being rubbed with a balloon. Some materials become electrically charged when rubbed with other materials. This occurs due to positive or negative charges that cause an electric force. Electric discharge is the removal of an electric charge from an object. When you walk across a rug, you gain an electric charge. Later, when you touch something and feel a shock, you become discharged. Some other examples of electric discharge are: lightening, electric shock, and wearing out a battery. An electric force is the attraction or repulsion between objects or particles that have an electric charge. Types of charge: There are two types of charge. + (positive) and (negative). An object with no charge is said to be neutral. Repulsion: When two objects having the same charge are brought close together, they push each other away (repel). Attraction: When two or more objects having opposite charges are brought together, they are attracted to each other. Attraction occurs when one object loses electrons to the other. For example, when two objects are rubbed together, one object may have a stronger attraction for electrons than the other object has. This object will take electrons from the other object. The object with the most electrons becomes negatively charged and the other object which has a shortage of electrons becomes positively charged. Laws of electric charges: 1. Opposite charges attract each other. 2. Similar (like) charges repel each other. 3. Charged objects attract neutral objects. 1 Science 9 Chapter 10 Current Electricity: (Pages 302-333) In static electricity, the electricity produced by rubbing materials together did not move. (Static= at rest). Once the electrons were transferred from one object to another, they were at rest. In current electricity, the electrons do not remain at rest, but move from one place to another. Current Electricity: The continuous movement of charged particles through a conductor. Conductor: A material that allows electricity to pass through it easily. Conduction: A transfer of energy through a material by the direct collision of particles. Energy from another source is needed to produce energy in the form of an electric current. Some common energy sources are batteries and generators. Detecting Current We can find out if there is a current in a wire by using a “current detector.” A detector allows us to compare the strengths of different currents. Ampere: The number of electrons moving past a point in one second. It is the unit for measuring electric current. Ammeter: A device used to measure strong electric currents (> 1 Amp). Galvanometer: A device used to measure weak electric currents (usually less than 1 mA). Electric (Chemical) Cells: Cell: A device that converts chemical energy into electric energy. Chemical cell: a chemical device for producing electric current. 2 Battery: Two or more cells joined together to produce an electric current. Volt: A unit used to measure the energy of charges delivered by a cell. The more voltage a cell has, the more energy is supplied to the electrons that leave the cell to produce an electric current. Voltmeter: A device used to measure the voltage produced in an electric charge. Electrode: Part of an electric cell that allows electrons to enter or leave the cell; it is usually made of a metal or of carbon. Electrolyte: A solution that conducts electricity (can be found in a cell). The wet cell: This is a cell made from an electrolyte liquid and 2 electrodes placed in a beaker or similar container An electrolyte solution is one that will conduct electricity. Eg. Acids, salt water, bases. The two electrodes MUST be different conducting materials, eg. Carbon and Zinc or else the wet cell will not work. The amount of electrical current a wet cell produces depends on: 1) The concentration of the electrolyte solution. Eg, Strong acid will conduct more electricity than weak acid. 2) The types of electrodes used. Electric cell structure and operation All cells have 2 parts in common 1) They all have electrodes, each one made from a different metal 2) They all have their electrodes separated with an electrolyte solution between them How cells generate an electric current: (How they work) 3 A chemical reaction between the chemicals in the electrolyte and the zinc electrode causes extra electrons to build up on the zinc electrode. At the same time, the carbon electrode loses electrons. The zinc electrode has more electrons than the carbon electrode. So, we say the carbon electrode is + and the zinc one is negative. If a connecting wire is placed between the + and terminals, the imbalance of electrons causes a flow of electrons from the + carbon terminal to the – zinc terminal. Resistance: A measure of how much a material resists the passing of electricity through it. Poor conductors resist electric flow. Because of this, they give off heat (and may even catch on fire). Wire diameter (thickness) and wire length can affect resistance. The thicker the wire, the less the resistance. The longer the wire, the greater the resistance. Resistor: A device made from a material that resists the flow of electricity. The greater the resistance of a material, the greater the amount of energy the electrons give up as they pass through the resistor. Eg: An ordinary light bulb. The filament that glows to give us light is made from a very resistant metal called tungsten. As electrical current meets the tungsten filament, it tries to “push through”. The tungsten resists the flow, so it heats up. This causes it to glow, giving off light. Heating elements of stove, toasters, kettles, are all resistors. Televisions and other appliances contain resistors. Circuits; Series and Parallel: (Section 10.1_Page 302). Load: An electric device Source: A cell (or battery) Conductor: The wire 4 Series vs. Parallel Circuits: (Section 10.2_Page 307). Series Circuit: One in which the electrons flow through each device along a single connecting path. (Eg: The removal of one bulb in the circuit causes all the rest to go out) Diagram of a Series Circuit: Figure 3; Page 307 Parallel Circuit: An electric circuit that provides alternate conducting paths for an electric current. (Eg: Remove one bulb, the others stay lit). Analogy: Block a river with a dam; water stops downstream unless there are other smaller rivers it can enter to go around the dam. Switch: A device used to open or close an electric current. Switch=open-- power off Switch=closed– power on Diagram of a parallel circuit: Circuit symbols: Figure 3; Page 307 Page 536; Table 9 5 Factors which affect the quantity of electric current in series and parallel circuits: 1) The source voltage: The higher the source voltage, the greater the current flowing 2) Resistance of the conductor: The lower the resistance, the greater the flow (quantity) of current. The higher the resistance, the lower the current flow will be. 3) The diameter (thickness) of the wire conductor: The thinner the wire, the less current it can conduct. The thicker the wire, the more current it can conduct 4) The distance of the circuit: Resistance will increase with distance so current will decrease the further the load is from the source. 5) The type of material the conductor is made from: Copper is a good conductor. So are carbon, gold, and silver. Gold is probably the best one but it is far too expensive to use for everyday wiring. 6