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Electric Current and Resistance

Electric Current and Resistance. Chapter 19 Sections 1 & 2. Current. Current – The rate at which electric charges move through a given area. Units for current is called, “Amperes” A Amps 1 Amp = 1 Coulomb of Charge per Second. Current vs. Voltage.

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Electric Current and Resistance

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  1. Electric Current and Resistance Chapter 19 Sections 1 & 2

  2. Current • Current – The rate at which electric charges move through a given area. • Units for current is called, “Amperes” • A • Amps • 1 Amp = 1 Coulomb of Charge per Second

  3. Current vs. Voltage • Current is the flow of electrons through a conducting material. • Voltage is the pressure in the conducting material that pushes the electrons. • Voltage can exist without current. • Current can not exist with out voltage.

  4. Electrical Current

  5. Batteries • Batteries act as pumps that push charge through a conducting material to create a current. • Batteries do no create charge! • Turn chemical energy into electrical energy. • Electrical energy is consumed when used, not charge.

  6. AC vs. DC Current • Direct current is when charges move in only one direction. • Batteries • Alternating current is when the terminals of potential difference are constantly changing sign. Hence there is no net motion of the charge. • Charges vibrate back and forth • Power lines

  7. Resistance • Resistance – Ratio of the potential difference across a conductor to the current it carries. • Units for resistance is an, “Ohm” • Greek Letter Omega “Ω” • Example: • R = 34 Ω (34 ohms)

  8. Resisting the Flow or Charge • Resistance in the flow of charge can be related to friction of a moving object. • The resistance holds back the electrons from flowing freely through the conductor. • Heat is formed as a result.

  9. Applications of Resistors • Resistors are used to control the amount of current in a conductor. • They do not change the potential difference (voltage) • They are used in mostly all electrical devices from televisions to microchips.

  10. Factors That Affect Resistance • Length • The longer the conductor, the more resistance to the flow of charge. • Cross-Sectional Area • The smaller the cross-sectional area of the conductor, the more resistance. • Material • Some objects allow the flow of charge more easily then others. • Iron has more resistance then copper. • Temperature • The warmer the conductor, the more resistance

  11. Ohm’s Law • Ohm’s Law states that voltage, current and resistance all affect one another.

  12. Superconductors • Superconductors – A material whose resistance is zero at or below some critical temperature, which varies with each material. • By decreasing the temperature of a conductor, the resistance to the flow of charge also decrease.

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