ch34_mksb

Maura Kearns, Sydney Bader Physics, Period 8

__ Vocabulary __ __ 34-1: Flow of Charge __ - When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other. - // Potential difference // – difference in potential (voltage) - The flow of charge will continue until both ends reach a common potential. - With no potential difference, there is no longer a flow of charge through the conductor. - To attain a sustained flow of charge in a conductor, potential difference must be maintained while charge flows from one end to the other. - __ 34-2: Electric Current __ - // Electric current // – the flow of electric charge. - Electrons carry the charge through the circuit of the solid conductors because they are free to move through the atomic network. - Protons are bound inside atomic nuclei that are more or less locked in fixed positions. - In fluids, positive and negative ions and electrons compose the flow of electric charge. - // Ampere // – the measure of electric current; SI unit: A. An ampere is the flow of 1 coulomb of charge per second. - Current-carrying wire does not have a net electric charge.
 * __ Chapter 34: Electric Current __**
 * Potential difference
 * Electric current
 * Ampere
 * Voltage source
 * Electric resistance
 * Direct current (dc)
 * Alternation current (ac)
 * Diode
 * Electric power

__ 34-3: Voltage Sources __ - Charges do not flow unless there is a potential difference. - // Voltage source // – something that provides a potential difference



-- It is not practical to have a voltage source whose two potentials equalize in one brief surge of moving charges. - Dry cells, wet cells, and generators are capable of maintaining a steady flow. They supply energy that allows charges to move. - In dry cells and wet cells, generators supply energy that allows charges to move. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Generators convert mechanical energy to electric energy. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Voltage provides electric pressure to move electrons between the terminals in a circuit. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Power lines use electric converters to provide 120 volts delivered to home outlets. The alternating potential difference between the two holes in the outlet has an average of 120 volts. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Charges flow through a circuit because of an applied voltage. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Voltage does not move; only charges

__ 34-4: Electric Resistance __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The amount of current flowing in a circuit depends on the voltage provided by the voltage source. Also dependant on electric resistance. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- // Electric resistance // – the resistance that the conductor offers to the flow of charge. <span style="font-size: 12pt; font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">

<span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The resistance of a wire depends on the conductivity of the material used in the wire as well as the thickness and length of the wire. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Thick wires have less resistance than thin wires. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Longer wires have more resistance than short wires. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The greater the motion of atoms within the conductor, the greater resistance the conductor offers to the flow of charge. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- For most conductors, increased temperature means increased resistance.

__ 34-5: Ohm’s Law __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The current in a circuit is directly proportional to the voltage impressed across the circuit, and it is inversely proportional to the resistance of the circuit. <span style="color: purple; font-family: 'Courier New'; mso-fareast-font-family: 'Courier New'; msofareastfontfamily: 'Courier New'; msolist: Ignore;">o Current = (voltage)/(resistance) <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Ohm’s Law – the relationship between voltage, current, and resistance. <span style="color: purple; font-family: 'Courier New'; mso-fareast-font-family: 'Courier New'; msofareastfontfamily: 'Courier New'; msolist: Ignore;">o 1 ampere = 1 (volt/ohm)

__ 34-6: Ohm’s Law and Electric Shock __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Shock in the human body is caused by current passing through the body. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The resistance of the human body is dependent on its condition and ranges from about 100 ohms (soaked in salt water) to 500,00 (totally dry). <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- For birds sitting on an electrical wire to feel a shock, there must be a difference in electric potential. They must be touched two wires.
 * Current in amperes || Effect ||
 * .001 || Can be felt ||
 * .005 || Painful ||
 * .010 || Involuntary muscle spasms ||
 * .015 || Loss of muscle control ||
 * .070 || Serious heart disruption, most likely fatal if lasting for more than 1 second ||

__ 34-7: Direct Current and Alternating Current __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- // Direct current // – a flow of charge that always flows in one direction. Example: battery (the terminals of the battery always have the same sign of charge)



<span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- // Alternating current // – electrons move first in one direction and then in the opposite direction. Example: commercial ac circuits



<span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Voltage in ac in North America is normally 120 volts <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Voltage in ac in Europe is 220 as the standard <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Most electric service in the US operates on a three-wire system; one wire at 120 volts positive, one wire at 0 volts (neutral), one wire at negative 120 volts.

__ 34-8: Converting AC to DC __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- // Diode // – tiny electronic device used as a one-way valve to allow electron flow in only one direction <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- A capacitor slows changes in current flow.

__ 34-9: The Speed of Electrons in a Circuit __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- An electric field is established inside the wire when a batter or generator is connected to a metal wire <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The electric field outside the wire is determined by the location of electric charges. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The electric field inside the wire runs directly along the wire <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- In dc circuit, the electric field lines are maintained in one direction in the conductor <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- In ac circuit, the conduction electrons don’t make any net progress in any direction.

__ 34-10: The Source of Electrons in a Circuit __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- The source of electrons in a circuit is the conduction circuit material itself. <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Energy (not electrons) carries from ac outlet into what is plugged in <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">-  Energy is carried by the electric field and causes a vibration of the electrons that already exist in the plugged in object <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- When shocked by an electric shock, energy causes free electrons in your body to vibrate in unison.

__ 34-11: Electric Power __ <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- // Electric power // – the rate at which electric energy is converted into another form <span style="color: purple; font-family: 'Courier New'; mso-fareast-font-family: 'Courier New'; msofareastfontfamily: 'Courier New'; msolist: Ignore;">o Electric power = current * voltage <span style="font-family: Symbol; mso-fareast-font-family: Symbol; mso-bidi-font-family: Symbol; msofareastfontfamily: Symbol; msolist: Ignore; msobidifontfamily: Symbol;">- Power is expressed in watts when voltage is in volts and current is in amperes <span style="color: purple; font-family: 'Courier New'; mso-fareast-font-family: 'Courier New'; msofareastfontfamily: 'Courier New'; msolist: Ignore;">o   1 watt = (1 ampere) * (1 volt)