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Current and Resistance

Current and Resistance. Electric Current. Current and Charge Movement. Current – the rate at which electric charges move through a given area Movement of electric charge Symbolized by I and measured in amperes (A) 1 A = 1 C/s

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Current and Resistance

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  1. Current and Resistance Electric Current

  2. Current and Charge Movement • Current – the rate at which electric charges move through a given area • Movement of electric charge • Symbolized by I and measured in amperes (A) • 1 A = 1 C/s • Electric current = (charge passing through a given area) / (time interval) • I=ΔQ/Δt

  3. Current and Charge Movement • Current is based on the movement of charge carriers • Electrons (negative charge) and protons (positive charge) • However, the general convention for current assumes motion of positive charge • Because current was defined by Ben Franklin before the structure of the atom was known • Materials that have free electrons are good electrical conductors and current easily passes through • Metals • Ions in solution (electrolytes)

  4. Drift Velocity • Drift velocity (vdrift)– the net velocity of a charge carrier moving in an electric field • Charge carriers are set in motion by electric forces generated by electric fields • This motion creates current • Motion is random due to particle collisions, but overall in the opposite direction of the electric field • Drift velocities are very small

  5. Sources and Types of Current • Batteries supply chemical energy to be converted to electrical potential energy which is then converted into kinetic energy by the electronic device • Generators convert different forms of mechanical energy (such as kinetic in hydroelectric dams) into electrical potential energy which is then transformed into kinetic energy by electrical devices

  6. Sources and Types of Current • Two types of current: alternating current (ac) and direct current (dc) • Classified on whether or not the direction of the current changes • Direct - current does not change direction • Batteries • Have positive and negative terminals • Alternating – current continually reverses direction • Wall outlets • No net motion of charge carriers • Vibrate back and forth • Must change direction very rapidly to avoid flickering • In the US, the ac frequency is 60Hz

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