# Chapter 23 Physics- Electric Current

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 Just as water flows from a region of high pressure to a region of low pressure, electric charge flows from a region of high electric pressure to a region of low electric pressure. Just as in hydraulic circuits there is water pressure, in electric circuits there is voltage An ampere is a unit of electric current Electrons flow in a wire when there is a potential difference across its ends. A suitable electric pump in an electric circuit is a generator & chemical battery It is correct to say that in electric circuits *voltage is the ratio of energy per charge. *voltage is applied across a circuit. *flowing charge is current. *charge flows through a circuit. A coulomb of charge flowing in a bulb filament powered by a 6-volt battery is provided with 6 joules If you stretch a copper wire so that it is thinner, the resistance between its ends increases Two light bulbs are connected to a battery, one at a time. The bulb that draws more current has the lower resistance, and is brightest. When you turn on a lamp, the initial current in its filament is greater at first, rather than a moment later, which indicates increased temperature means increased resistance. Electric resistance in our skin is lowered when our skin is moist Current in a conductor can be increased by *reducing its resistance. *increasing the voltage across it. The resistance of a filament that carries 2 A when a 10-V potential difference across it is 5 ohms Two lamps with different filament thicknesses, and therefore different resistances, are connected in series. Greater current is in the lamp with the same in each If an electric toaster rated at 110 V is accidently plugged into a 220-V outlet, the current drawn by the toaster will be twice its normal value The current in two identical light bulbs connected in series is 0.25 A. The voltage across both bulbs is 110 V. The resistance of a single light bulb is 220 ohms Direct current is normally produced by a battery Alternating current is normally produced by a generator Current that is typically 60 hertz is alternating current A capacitor is useful in smoothing pulsed current An electric diode is useful for changing ac to dc For electric current in the home, your power company supplies energy The source of electrons in a simple electric circuit is the electrical circuit itself Electrons that are energized to glow in the filament of a common ac lamp are electrons already in the filament. The number of electrons delivered daily to an average American home by an average power utility in the early 21st century was zero When Eddie Electron experiences an electrical shock, the source of electrons composing the shock is eddie’s body Electrons flow in an electrical circuit by Electrons flow in an electrical circuit by The drift speed of electrons that compose current in a flashlight is about less than 1 cm/s. The electric field established by a generator in an ac circuit changes magnitude and direction with time. Power is defined as the energy expended per unit of time. When translated to electrical terms, power is equal to current multiplied by voltage. In units of measurement, power in watts is equal to amperes x volts. One joule per coulomb is a unit of voltage. One kilowatt is a unit of power One kilowatt-hour is a unit of energy. The electric power supplied to a lamp that carries 2 A at 120 V is 240 watts. A 100-W lamp glows brighter than a 25-W lamp. The electrical resistance of the 100-W lamp is less The energy dissipated in a light bulb in a circuit is provided by the voltage source. A 60-W light bulb connected to a 120-V source draws a current of 0.5 A. The power consumed by a device drawing 0.8 A when connected to 120 V is 96 W. A power line with a resistance of 2 ohms carries a current of 80 A. The power dissipated in the line is 12,800 W. A 60-W and a 100-W light bulb are rated at 120V. Which bulb has a higher resistance? 60-W bulb A 60-W and a 100-W light bulb are connected in parallel to a 120-V outlet. Which bulb draws more current? 100-W bulb The current drawn by a 1200-W toaster connected to 120 V is 10 A. The resistance of the toaster coils is 12 ohms. A heater draws 20A when connected to a 110-V line. If the electric power costs 20 cents per kilowatt hour, the cost of running the heater for 10 hours is \$4.40. A lamp rated 23W 120V means that it will deliver 23 W when the voltage across it is 120 V. The amount of current in a CFL rated 23W 120V is about 0.2A. If you wish to keep chicken warm in a shed on a cold night, the best lamp to use is an incandescent lamp. By convention, the direction of current in a circuit is *the direction in which positive charge flows. *from the positive terminal of a source to the negative terminal. When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is less than the resistance of either lamp. On some early automobiles both headlights failed when one bulb burned out. The headlights were likely connected in series. Compared to a single lamp connected to a battery, two identical lamps connected in series to the same battery will carry less current. Connect a pair of lamps in series and current is drawn from the battery. Connect the same lamps in parallel and the current drawn is more The safety fuse in an electric circuit is connected to the circuit in series As more lamps are connected in a series circuit, the overall current in the power source decreases To connect a pair of resistors so their equivalent resistance (the single resistor having their combined value) will increase, connect them in series The equivalent resistance of any parallel branch in a circuit is always less than the resistance of the lowest resistor. A 4-ohm and 6-ohm resistor connected in parallel have an equivalent resistance of 2.4 ohms. Three resistors take the shape of a triangle, one resistor in each leg. Resistance in one leg is 4 ohms, 6 ohms in a second leg, and a third leg 10 ohms. Connecting an ohm-meter across the 10-ohm resistor will show the equivalent resistance to be 5 ohms. The equivalent (combined) resistance of 1-ohm, 2-ohm, and 3-ohm in series is about 6 ohms.

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