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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 is 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. Ohm’s Law: V = I x R Used to determine V, I, & R at all parts of a circuit. It means: • A 1V circuit with a 1Ω Resistance will produce a current of 1A. • Adding more resistors to a circuit will decrease the current produced. • Increasing the voltage will increase the current produced.

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

  17. 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

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

  19. Power = the rate of doing work (Work/time) Electrical Power = Current x Voltage P = I x V Units: Watts

  20. 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

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

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

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

  24. 22.2 Using Electrical Energy Electric companies measure Energy consumption in Kilowatt-hours. 1 kW h = 3.6 X 106 J

  25. 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!

  26. 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

  27. 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.

  28. 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

  29. Power Electrical Energy is usually converted to • Electromagnetic Energy (light), • Thermal Energy (heat), • or Kinetic Energy (motion).

  30. 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

  31. Chapter 23 Series and Parallel Circuits

  32. 23-1 Simple Circuits Remember that there are 2 Types of circuits… Series & Parallel

  33. 2. Current Electricity * Electrons flow in a conductor. * Must have a closed circuit (loop). Charge = number of transferred electrons Measured in Coulombs (C)

  34. Current = electron flow (I) (like water flow) Measured in Amperes (A) Voltage = electrical potential energy (V) (like water pressure) Measured in Volts (V)

  35. Resistance = ease that current can flow (like pipe diameter) Measured in Ohms (Ω) Resistor = item in circuit that causes resistance. Resistors “use up” a circuit’s voltage. Ex: Light Bulb

  36. Circuit = the path that flowing electrons follow If path is continuous, it’s a closed circuit and electricity can flow. If path is interrupted, it’s an open circuit and electricity can NOT flow.

  37. Series Circuits • Current goes through one pathway only. • Same amount of current goes through each component (battery, resistor, etc.). • The total resistance of resistors in series = the sum of each resistance (add them up).

  38. Series Circuit

  39. In a series circuit, all of the Resistors are added together In order to get the Equivalent Resistance. R = R1 + R2 + R3 + … See that the equivalent resistance Is greater than any individual Resistor, therefore if the voltage Does not change, adding more Resistors always decreases current

  40. PROBLEM... Three 20 Ω resistors are connected In series across a 120 V generator. What is the equivalent resistance Of the circuit? What is the current In the circuit? R = 60 Ω I = 2.0 A

  41. Parallel Circuits • Current divides into 2 or more paths • Voltage drop across components is equal. • The sum of the current in each parallel path = the total current in (or out) of the circuit.

  42. Parallel Circuit

  43. In a parallel circuit the resistance Is always smaller than any One resistor because there are More branches for the current To flow through. Equivalent Resistance for Parallel 1/R = 1/R1 + 1/R2 + 1/R3 + …

  44. PROBLEM... Three 15 Ω resistors are connected In parallel and placed across A 30 V battery. What is the Equivalent resistance? What is the Current through the entire circuit? What is the current through each Branch of the circuit? R = 5 Ω I = 6 A I = 2 A

  45. PROBLEM... Draw a circuit diagram of a series circuit and a Parallel circuit that each contain The following… Battery, motor, 3 lights, and 2 Resistors.

  46. 23-2 Applications There are many safety devices When dealing with electrical Circuits. A short circuit is when the Resistance is very small which Makes the current very large.

  47. When a short happens enough Thermal energy is produced to Start a fire, or just melt the Wires if you’re lucky. A fuse is used to help stop a short Before it gets too bad. When a fuse is connected to the circuit it will melt and “blow” Before the wires do.

  48. A circuit breaker is another kind Of fuse. It breaks the circuit when the Current gets too high and a Switch flips. In order to fix The circuit, all you have to do is Flip the switch back.

  49. A ground fault interrupter (GFCI) is a kind of electrical outlet that Breaks the circuit at the plug Instead of the circuit/fuse box.

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