Ohm’s law

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Ohm’s law

  1. 1. OHM’S LAW<br />By: Mr. Augosto M. Directo<br />
  2. 2. Voltage, Current and Resistance<br />Voltage is the amount of energy per charge move electrons in one point to another in a circuit. It is measured in volts (v)<br /> Current is the rate of charge flow and it is measured in amperes (A). Its unit is (I).<br />Resistance is the opposition of current and it is measured in ohms (W)<br />
  3. 3. DC Current vs. AC Current <br />The current from a battery is always in the same direction. <br />One end of the battery is positive and the other end is negative. <br />The direction of current flows from positive to negative. <br />This is called direct current, or DC.<br />
  4. 4. DC Current vs. AC Current <br />If voltage alternates, so does current.<br />When the voltage is positive, the current in the circuit is clockwise.<br />When the voltage is negative the current is the opposite direction. <br />This type of current is called alternating current, or AC.<br />
  5. 5. Series and Parallel Circuit<br />In a series circuit , the current through each of the components is the same, and the voltage across the components is the sum of the voltages across each component.<br />In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.<br />
  6. 6. Series Vs. Parallel<br />Series Circuits<br /><ul><li>A series circuit is a circuit in which the current can only flow through one path.
  7. 7. Current is the same at all points in a series circuit</li></ul> Parallel Circuits<br />In contrast, in a parallel circuit, there are multiple paths for current flow.<br />Different paths may contain different current flow. This is also based on Ohms Law<br />Total resistance will be less than the smallest resistor<br />
  8. 8. In Series circuit; the total current is equal<br />Rtotal = R1 + R2 + R3<br />Vtotal = V1+ V2+ V3<br /> In Parallel Circuit; the total voltage is equal<br />1 = 1 +1 + 1 + 1 <br />Rtotal R1 R2 R3Rn<br />Itotal = I1+ I2+ I3<br />
  9. 9. By Analogy: Series Vs Parallel<br />I<br />E<br />R2<br />R1<br />R1<br />I1<br />E<br />R2<br />I2<br />R3<br />I3<br />
  10. 10. Advantages of parallel circuits<br />Parallel circuits have two big advantages over series circuits:<br /> 1. Each device in the circuit sees the full battery voltage.<br /> 2. Each device in the circuit may be turned off independently without stopping the current flowing to other devices in the circuit.<br />
  11. 11. Ohms Law<br />States that the voltage is directly proportional to the current in the circuit.<br />It is discovered by the German Physicist George Simon Ohm.<br />Ohm’s law is: <br />V = IR ,<br /> I = V/R, <br />R= V/I<br />
  12. 12. Unit Modifiers for Reference<br />Smaller<br />Deci = 10-1<br />Centi = 10-2<br />Milli = 10-3m<br />Micro = 10-6<br />Nano = 10-9<br />Pico = 10-12p<br />Fento = 10-15<br />Larger<br />Kilo = 103k<br />Mega = 106<br />Giga = 109<br />Tera = 1015<br />
  13. 13. Series Circuit Analysis<br />Example #1<br />A 4v battery is placed in a series circuit with a 2 resistor.<br />What is the total current that will flow through the circuit?<br />2<br />4v<br />I = ?<br />
  14. 14. Solution<br />Given:<br />V = 4v<br />R = 2<br />I = ?<br />I = V/R<br /> = 4v/2<br />I = 2A<br />
  15. 15. Example#2<br />A 110v supplies a load with a resistance of 3,5, and 7 respectively, find the current in the circuit?<br />3<br />5<br />I = ?<br />110v<br />7<br />
  16. 16. Solution<br />Given:<br />V= 110 v <br />R1 = 3<br />R2 = 5<br />R3 = 7<br />I = ?<br />Rtotal = R1 + R2 + R3 I = V/R<br /> = 3 + 5 + 7 = 110/12<br /> = 12 = 9.17 A<br />
  17. 17. Parallel Circuit Analysis<br />Example # 3 <br />A 220v is connected in parallel with the load. It has a resistance of 5ohms and 10ohms. Find the Total current and the I1and the I2<br />10<br />5<br />220v<br />
  18. 18. Solution<br />Given:<br />V=220v<br />R1 = 5<br />R2 = 10<br />I1 = V/ R1 I2 = V/ R2<br /> = 220 / 5 = 220 / 10<br /> = 44 A = 22 A<br />RT = R1R2 / R1 + R2IT = V / RT<br /> = (5 x 10) / 15 = 220/3.33<br /> = 3.33 = 66.06A <br />
  19. 19. Example #4<br />Find the total voltage and the total resistance of the load if the total current is 15A and it has a R1 of 6 ohms and R2 of 2 ohms.<br />6<br />V=?<br />2<br />IT =15<br />
  20. 20. Solution<br />Given:<br />R1 = 6<br />R2 = 2<br /> IT =15 A<br />RT = R1 R2 / R1 + R2VT= IT/ RT<br /> = (6 x 2) / 8 = 15 A x 1.5 <br /> = 1.5  = 22.5 v<br />I1 = V/ R1 I2 = V/ R2<br /> = 22.5 / 6 = 22.5 / 2<br /> = 3.75 A= 11.25 A<br />
  21. 21. Electric Power, AC, and DC Electricity<br />The watt (W) is a unit of power. <br />Power is the rate at which energy moves or is used.<br />Since energy is measured in joules, power is measured in joules per second. <br />One joule per second is equal to one watt.<br />
  22. 22. Power in electric circuits<br />One watt is a pretty small amount of power. <br />In everyday use, larger units are more convenient to use. <br />A kilowatt (kW) is equal to 1,000 watts.<br />The other common unit of power often seen on electric motors is the horsepower.<br />One horsepower is 746 watts.<br />
  23. 23. Formula of Power<br /> Power (watts)<br />Voltage (volts)<br />P = VI<br />Current (amps<br />
  24. 24. Example # 5<br />A light bulb with a resistance of 1.5Ω is connected to a 1.5-volt battery in the circuit shown at right. <br />Calculate the power used by the light bulb.<br />
  25. 25. Solution<br />Given:<br />V = 1.5v<br />R = 3<br />I =V / R P = V I<br /> = 1.5 / 3 = 1.5 x 0.5<br /> = 0.5 A = 0.75 watts<br />
  26. 26. Paying for electricity<br />Electric companies charge for the number of kilowatt-hours used during a set period of time, often a month.<br />One kilowatt-hour (kWh) means that a kilowatt of power has been used for one hour. <br />Since power multiplied by time is energy, a kilowatt-hour is a unit of energy.<br />One kilowatt-hour is 3.6 x 106 joules.<br />
  27. 27. Exercises:<br />I. Identification:<br />Direction: Identify the following questions.<br />1. It is the amount of energy per charge move electrons in one point to another in a circuit. It is measured in volts?<br />2. It is a type of current which the current from a battery is always in the same direction?<br />3. It is the opposition of current?<br />4.It is the rate of charge flow?<br />5. It is the rate at which energy moves or is used?<br />
  28. 28. 6. One horsepower is equivalent to how many watts?<br />7. In series circuit the total _______ is equal /the same.<br />8. In parallel circuit the total _______ is equal/the same.<br />9. A circuit where the voltage across each of the components is the same, and the total current is the sum of the currents through each component.<br />10. It States that the voltage is directly proportional to the current in the circuit.<br />11. A circuit where the current through each of the components is the same, and the voltage across the components is the sum of the voltages across each component.<br />12. Ohm’s Law is discovered by whom a German Physicist.<br />
  29. 29. 13. what does kwh means?<br />14. How many joules are there in a kwh?<br />15. The other common unit of power often seen on electric motors is?<br />II. Problem Solving:<br />1. A 115 volt is connected in parallel with the load. It has a I1 3 A and R2 15 ohms. Find the IT and the RT.<br />I1<br />115v<br />I1 = 3A<br />15 <br />
  30. 30. 2. Resistors 1, 2 ,3 has a resistance of 4 , 8  and 12  are connected in series with a total current of 25 A. Find the total voltage and the V1 , V2 , V3.<br />3. A motor has a voltage of 220 volts and a resistance of 35. Find the current and the power.<br />V1<br />4 <br />IT = 25A<br />VT = ?<br />8<br />12<br />
  31. 31. Key Answers<br />I. Identification<br />1. voltage<br />2. direct current<br />3. resistance<br />4. current<br />5. power<br />6. 746watts<br />7. current<br />8. voltage<br />
  32. 32. 9. Series Circuit<br />10 Ohm’s Law<br />11. Parallel Circuit<br />12. George Simon Ohm<br />13. kilo watt hour<br />14. 3.6 x 106joules<br />15. horsepower <br />II. Problem Solving<br />1. Given:<br />V = 115 v R2 = 15 <br />I1 = 3A<br />R1 = V / I1 I2 = V/ R2 RT = R1 + R2IT = V/ RT<br /> = 115/ 3 A = 115/15 = 15 + 38.33 = 115 / 53.33<br /> = 38.33  = 7.67A = 53.33 = 2.16A<br />
  33. 33. 2. Given:<br />R1 = 4<br />R2 = 8 <br />R3 = 12<br />IT = 25A<br />V1 = ITR1 V2 = ITR2 V3 = ITR3<br /> = 25 x 4 = 25 x 8 = 25 x 12 <br /> = 100 v = 200v = 300v<br />RT = R1 +R2 +R3 VT = ITRT<br /> = 4 + 8 + 12 = 25 x 24<br />= 24  = 600v<br />
  34. 34. 3. Given:<br />V= 220v<br />R = 35 ohms<br />Find: I? P?<br />I = V/R P = V I<br /> = 220 / 35 = 220 x 6.29<br /> = 6.29A = 1382.86 watts<br />
  35. 35. Thank You<br />God Bless<br />

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