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Module 8 Lesson 1 Notes Presentation Guided Notes KEY What is electric charge? There are positive and negative charges. An atom has equal numbers of protons and electrons, which means that the positive and negative charges cancel out. So, an atom has no net electric charge. It is said to be electrically neutral. When there are transfers of charges, it is STATIC ELECTRICITY. For example, when the electrons are transferred from the carpet to your shoes, the accumulation of excess electric charge on your shoes is called static electricity. Electric charges exert forces. Unlike charges attract each other. Like charges repel each other. As the distance between charged objects increases, the attractive force decreases. Conductors are materials in which electrons can easily flow. For electricity, the best conductors are metals. The atoms in metals have loosely held electrons that make it easy for electricity to flow through them. Insulators are materials in which electrons cannot easily flow. Unlike in conductors, electrons in insulators are held tightly, such as in plastics. Plastics cover electric cords to prevent you from getting shocked. Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. This charging at a distance is induction. When two charged objects are touched to each other, electrons will rearrange their positions between each other. This charging by touching is conduction. When two different types of materials are rubbed together, the charged particles will rearrange themselves on each object. This charging by touching of two different materials is charging by friction. Let’s look at lightning. Eventually, enough charge builds up to cause a static discharge between the cloud and the ground. As the electric charges move through the air, they collide with atoms and molecules. These collisions cause the atoms and molecules in air to emit light. Lightning also creates powerful sound waves. The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat. The heat causes air in the bolt's path to expand rapidly, producing sound waves that you hear as thunder. A discharge can occur any time that charge builds up in one area. Providing a path for charge to reach Earth prevents any charge from building up. Earth is a large, neutral object that is also a conductor of charge. Any object connected to Earth by a good conductor will transfer any excess electric charge to Earth. Connecting an object to Earth with a conductor is called grounding. Forms of Electricity Electricity occurs in two different forms: • • Static This type of electricity is stationary. It occurs in one place at one time. Current This type of electricity moves. It flows around a circuit. Static Electricity occurs with materials which are insulators, such as plastic. Rubbing adds or removes electrons, so the rubbed object becomes charged. Remember: Like objects repel, unlike attract. Current Electricity is when electrons flow through a conductor, such as copper. Flow is from negative to positive and circuits create a continuous loop for electrons to flow. Requires an energy supply, but also, it uses energy. CIRCUIT TYPES The simplest type of circuit involves electricity going around with no “choices” (electrons don’t really choose). This is called a Series circuit. The other main type of circuit has two or more branches. This is called a Parallel circuit. Series circuit has a single loop for electrons to travel around, so they can only go in one direction. Components are connected one after another, or in “series”. Current has to travel through all components and current is the same at all points. Voltage is shared between components. Parallel circuit has two or more paths for electrons to travel, so electrons have options. Current is shared between the branches and the sum of the current in each branch equals total current. Voltage loss is the same across all components Electricity is forced around a circuit by an electrical force field. Flow of electricity around a circuit is called CURRENT (I) and it is measured in amps (A). Voltage (V) is the increase or decrease in the amount of electrical energy carried by the current. Current (I) is the flow of electrons around a circuit. DC is direct current, such as in a battery that you would put in a flashlight. In DC currents, electrons flow in one direction. AC is Alternating current, such as the current that runs through your home. Electron flow changes direction 50x per second. Ammeter measures CURRENT(I), which is the flow of electrons. The unit is Amps (A). To measure Amps, connect the ammeter in the series at the point you wish to measure. Voltage (V) is the gain or loss of energy as it passes through a component. Voltage lost equals voltage gained. In series circuits, voltage loss is shared between components. In parallel circuits, voltage loss is the same across all components. Voltmeter measures voltage in Volts (V). Voltage increases as it passes through energy suppliers. Voltage is decreased as it passes through energy users. To measure voltage, connect voltmeter in parallel circuit around a component. Power is energy used by component per second and is measured in the unit of the Watt, symbol is W. One watt means that 1 joule of electrical energy is being used up per secondHousehold Circuits The wiring in a house must allow for the individual use of various appliances and fixtures. This wiring is mostly a combination of parallel circuits connected in an organized and logical network. The main switch and circuit breaker or fuse box serve as an electrical headquarters for your home. Parallel circuits branch out from the breaker or fuse box to wall sockets, major appliances, and lights.