Electricity and Magnetism Study Guide (8th Grade)

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Charge
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A physical property resulting from the collection of, or dispersion, of electrons.
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Static Electricity
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A buildup of charges on an object. Generally produced by friction or induction.
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Charge via Friction
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As two objects rub together, electrons from one object are transferred from one to the other.
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Induction
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Description: A negative(ly) charged object – when placed near a neutral object – causes the electrons on another object to be repelled, leaving a positively charged surface because only the electrons can move – the protons are locked in place by the nucleus.
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Conduction
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Description: A negatively charged object (like a plastic ruler) transfers some of its electrons to a neutral object when they touch.
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Electricity
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A form of energy caused by the movement of electrons. The flow of electrons.
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Direct Current
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Direct current (known as DC) is a current that flows through a conductor in one direction only.
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Direct Current Examples
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Battery powered laptops, cellphones or flashlights.
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Alternating Current
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Alternating Current (known as AC) and is a flow of electric charge that regularly reverses directions.
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Alternating Current Examples
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In anything used in your home or on the main power grid from the electric company: TV, vacuum cleaner, microwave.
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Voltage
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The potential difference measured in volts, and the amount of work to be done to move a charge from one point to another. The \”V\” in V=IR
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Current
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A movement of electrical charges around a closed path or circuit, measured in amperes (amps, A), the I in V=IR
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Resistance
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A material’s opposition to the flow of electric current. The R in V=IR
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V=IR
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The relationship between voltage, resistance and current. Voltage is equal to current times resistance (V=IR).
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Series Circuit Advantages
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It uses less wire and energy so your batteries will last longer.
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Series Circuit Disadvantages
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The current is shared, so each resistor gets less energy (i.e, each light bulb will be dimmer) and if one bulb breaks all others will stop working as well.
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Diagram: Series Circuit
Diagram: Series Circuit
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With Battery, Switch, and 3 Resistors
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Parallel Circuit Advantages
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The resistors each get the full benefit of the charge (i.e., lights will be brighter), and if one break all others continue to function.
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Parallel Circuit Disadvantages
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They require more energy so your battery won’t last as long, they use more wire as each resistor requires its own path.
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Diagram: Parallel Circuit
Diagram: Parallel Circuit
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With Battery, Switch, and 3 resistors.
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Magnet
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Any material that attracts iron or items that contain iron.
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Permanent Magnet
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A material that will retain its magnetism for a long time. Its domains will remain aligned (i.e., cobalt, nickel, iron).
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Electromagnet
Electromagnet
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A coil wrapped around an iron core that acts as a magnet when an electric current flows through the wire coil.
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Electromagnet Advantages
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Electromagnets can be turned on and off.
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Simple Motor Operation
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A current turns off and on, causing a magnet to spin.
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Magnetic Field Effects (on a Compass)
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The direction of a needle will change due to the magnetic field.
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Conductive Solutions
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Solutions that contain ions (electrolytes) that allow for the transfer of electrons (an electric current).
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Law of Electric Charges
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Opposite charges attract while like charges repel.
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Insulator
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A material that resists the flow of electrons.
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Conductor
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A material through which electrons can easily flow.
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Ohm’s Law Calculation
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V=IR, i.e., the voltage needed to make a current of 5A in a resistance of 15ohms is: V=5A x 15ohms =75v
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Current in Amperes
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V=IR, so I=V/R
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Poles
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The opposite ends of a magnet.
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Magnetic Force
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The push or pull that magnets exert on each other.
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Domains of an Atom for Magnetism
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The domains of an atom must all be aligned (going in the same direction) in order to be magnetic.
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Results of a Cut Bar Magnet
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It forms two smaller magnets, each with a north and south pole.

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