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7-2 Electric Current Notes What is an Electric Current? The ___________________________ through a wire of conductor is called ___________________________ Current is usually the flow of _____________________ Electric current is measured in __________________ (___) Charges flow from ___________ voltage to __________ voltage (_______ _______________________-must be present) A voltage difference is the ______________ that causes charges to move. Voltage difference is measured in ______________. For charges to flow, the wire must always be connected in a ____________ ____________________________ If the circuit is broken by removing the battery, or the lightbulb, or one of the wires, current will ______________________. Batteries To keep an electric current continually flowing in the electric circuit a voltage difference needs to be maintained in the circuit. A battery can provide the voltage difference that is needed to keep current flowing in a circuit. _______________________ as long as there is a __________________ that connects one battery terminal to the other battery terminal. Dry-Cell Batteries A cell consists of _____________________ surrounded by a material called an ____________________. The electrolyte enables charges to move from one electrode to the other. One electrode is the carbon rod, and the other is the zinc container. The electrolyte is a __________________ containing several chemicals. The cell is called a dry cell because the electrolyte is a moist paste, and not a liquid solution. Sources of Electricity A _________________________ produces a voltage difference between its _____________ container and its _______________ suspension rod, causing current to flow between them Sources of Electricity A ____________________________ contains two connected plates made of different ___________________ in a conducting _________________ A wet-cell battery contains several wet cells connected together. Sources of Electricity ____________________ have a voltage difference across the __________ _____________ of an electrical outlet, and a generator at a ______________ _________________ provides this voltage difference What is Resistance? ________________________________ _________________________ the _____________ of electrons electrical energy is converted to _______________________ &__________ all materials have ____________ electrical resistance Resistance is measured in ______________ (____) Making wires _________________________, or hotter ____________ the resistance Ohm’s Law Ohm’s Law – the current in a circuit equals the voltage difference divided by the resistance V: potential difference (V) I: current (A) V=I×R R: resistance () Voltage ________________ when ________________ increases. Voltage ________________ when ________________ increases. Ohm’s Law Problem A lightbulb with a resistance of 160 is plugged into a 120-V outlet. What is the current flowing through the bulb? Question 1 __________ is the net movement of electric charges in a single direction. A. An open circuit B. Electric current C. Proton flow D. Voltage Question 2 What is a volt? Answer Question 3 What is the tendency for a material to oppose the flow of electrons called? Answer What property of electric current causes light bulbs to give light? Notes 7-3 Electrical Circuits Electrical Circuits Circuits rely on generators at power plants to produce a _____________ __________________ across the outlet, causing the charge to move when the ______________________ Example Hair dryer plugged into wall outlet Generator at power plant produces voltage difference Dryer and circuit in house contain conducting wires to carry current Hair dryer turns electrical energy into thermal energy and mechanical energy Unplug hair dryer opens circuit and breaks path of current The Current in a Simple Circuit A simple electric circuit contains a source of ________________________, such as a battery, a device, such as a lightbulb, that has _________________, and ____________________ that connect the device to the battery terminals. When the wires are connected to the battery terminals, ________________ ____________________________in the ____________________________. Circuit Components A - battery B - switch C - light bulb D - resistor Types of Circuits _________________ circuit – the current has only ___________________ to flow through _________________ circuit – are used in ___________________________ _____________________________________ Series Circuit current travels in a _________________ path –_______________________ - one _________ ____________ the flow of current current is the ______________ throughout circuit –lights are ______________ brightness each device receives a ________________ of the total voltage –gets ________________ as lights are added ____________________ – if any part of a series circuit is disconnected, ____________________________________ through the circuit Example: _______________________ Parallel Circuit Parallel circuit – contains ______________________________ for current to move through. The current can flow through both or either of the branches. Example: _____________________________ Advantage When one branch of the circuit is opened, such as when you turn a light off, the current continues to flow through the other branches. Household Circuits Household circuits mainly use ________________circuits connected in a logical network. Electrical energy enters your home at the _________________________or _________________ and branches out to wall sockets, major appliances, and lights. Guards against overheating electric wires: ____________________________ – contains a small piece of metal that melts if the current becomes too high, opening the circuit and stopping the flow of current. To enable current to flow again in the circuit, you must _____________the blown fuse with a new one. Too many appliances in use at the _____________________ is the most likely cause for the overheating of the circuit. Household Fuse Box Guards against overheating electric wires: ______________________ – contains a small piece of metal that bends when it gets hot, opening the circuit and stopping the flow of current. Circuit breakers usually can be reset by pushing the switch to its “on” position. Breaker Box Electrical Power Electrical energy is easily converted to mechanical, thermal, or light energy. Electrical power – the __________________________________________ ______________________________________________________________ Electrical Power - rate at which electrical energy is ___________________ to another form of energy P: _________________ (____) I: _________________ (____) V: ________________________ (__) P=I×V Electrical Power is expressed in ________________________ The unit for power is the watt (W). Because the watt is a small unit of power, electric power is often expressed in ______________________ One kilowatt equals _________________________. P (watts) = I (amperes) x V (volts) To calculate the amount of energy an appliance uses: The unit of electrical energy is the kilowatt-hour, which equals 1000 watts of power used for one hour. Energy = power x time E (kWh) = P (kW) x t (h) Electrical Power A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use? Electrical Energy Electric companies charge by the amount of electrical energy used, rather than by the electric power used. Electrical energy usually is measured in units of kilowatt hours (kWh) and can be calculated from this equation: Electrical Energy –energy use of an appliance depends on power required and time used E: __________________ (__________) E=P×t P: __________________ (________) t: __________________ (_____) The Cost of Using Electrical Energy • The cost of using some household appliances is given in this table, where the cost per kWh is assumed to be $0.09/kWh. Electrical Energy A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day? Question 1 What is an open circuit? Answer Question 2 The rate at which electrical energy is converted to another form of energy is called __________. A. electrical fuse B. electrical switching C. electric power D. thermal energy Question 3 Which of the following equations is used to calculate electric power? A. P = IV B. P = I/V C. P = V/I D. P = AV Why do homes have a fuse box or circuit breaker? How does it work?