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Chapter 22 Current Electricity

Chapter 22 Current Electricity. 22.1 Current & Circuits. Electricity did not become an integral Part of our daily lives until Scientists learned to control the Movement of electric charge. This is known as current. Electric currents are responsible For many things; computers,

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Chapter 22 Current Electricity

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  1. Chapter 22 Current Electricity

  2. 22.1 Current & Circuits Electricity did not become an integral Part of our daily lives until Scientists learned to control the Movement of electric charge. This is known as current

  3. Electric currents are responsible For many things; computers, Cars, and every move you make. Current is the rate at which Electric charges move through A given area.

  4. Conventional current is defined In terms of positive movement. Electricity is the movement of Electrons, the negative charge, Moving in a direction. This direction Is in the positive direction.

  5. Solutions that have dissolved Ions can be charge carriers, These are called electrolytes. Drift velocity is the net velocity of a charge carrier moving in An electric field.

  6. Drift speeds are relatively small. The speed of an electron in a Copper wire is only about 0.000246 m/s! The electric Field, on the other hand, is Almost the speed of light.

  7. Batteries and generators Supply energy to charge carriers. Both batteries and generators Contain a potential difference (volts) across their terminals. Batteries use chemical energy And generators use mechanical Energy.

  8. Current can be direct or alternating. In Direct Current (DC) the charge Moves only one way through the Wire. (like my electric truck) In Alternating Current (AC), the Charges are constantly changing, Creating no real movement of Electrons. Our house current in the US is 60 Hz.

  9. Q t I = I = electric current Q = charge through a given area t = time

  10. The SI unit for current is the Ampere (A). The SI unit for charge is the Coulomb (C). So the Ampere is 1 C per second.

  11. PROBLEM... The amount of charge that passes Through the filament of a Certain light bulb in 2 s if 1.67 C. Determine the current in The light bulb. I = 0.835 A

  12. There are insulators and Conductors, but there are also Not so good conductors. The impedance of the motion of Charge through a conductor Is the conductor’s resistance. Resistance is the ratio of the Potential difference across A conductor to the current It carries.

  13. V I R = SI unit for resistance is the Ohm, And is represented by Ω.

  14. Ohm’s law states that the Resistance is constant over a Wide range of applied Potential differences. It is usually shown by… V = IR

  15. Resistance depends on length, Cross-sectional area, material, And temperature. Resistors can be used to control The amount of current In a conductor.

  16. PROBLEM... The plate on an iron states that The current in the iron is 6.4 A When the iron is connected across A potential difference of 120V. What is the resistance of the iron? R = 19 Ω

  17. Electric power is the rate of Conversion of electrical energy. P = IV The SI unit is the Watt.

  18. PROBLEM... An electric space heater is Connected to a 120 V outlet. The Heater dissipates 3.5 kW of power In the form of heat. Calculate The resistance of the heater. R = 4.1 Ω

  19. An electric circuit is a Continuous path through which Electric charges can flow. There are two types of circuit Connections, Parallel & Series

  20. A parallel circuit is one with Several current paths, whose Total current equals the sum of the Currents in its branches.

  21. A series circuit is one in which Current passes through one Device and then another.

  22. 22.2 Using Electrical Energy Electric companies measure Energy consumption in Kilowatt-hours. 1 kW h = 3.6 X 106 J

  23. Electrical energy is transferred at High potential differences to Minimize loss. (up to 1000000 V) When the wires are strung, they are Very tight and straight, they bow Because they are soooo hot!

  24. PROBLEM... How much does it cost to operate A 100 W light bulb for 24 hours If electrical energy costs $0.08 Per kW h? What is the cost per Year? What is the cost if you used A energy conserving bulb at 14 W? Cost = $0.19/day $69/year Cost = $ 0.03/day $9.81/year

  25. Current moving through a resistor Causes it to heat up because Flowing electrons bump into the Atoms in the resistor. These collisions increase the Atoms’ kinetic energy and, thus, The temperature of the resistor.

  26. If we rearrange Ohm’s Law, and The formula for power, we have 3 new formulas that we can use… And for the thermal Energy dissipated… P = I2R V2 R P = V2 R E = t

  27. PROBLEM... A heater has a resistance of 10 Ω. It operates on 120 V. What is the power dissipated by The heater? What is the thermal Energy supplied by the heater In 10 s? 1.44 kW 14.4 kJ

  28. THE END

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