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Ohm’s Law, Power and Energy

Ohm’s Law, Power and Energy. EE 2010: Fundamentals of Electric Circuits Mujahed AlDhaifallah. Ohm’s Law!. Current flows because Electrons flow from one point to another. What causes the flow of electrons?. Ohm’s Law!. Current flows because Electrons flow from one point to another.

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Ohm’s Law, Power and Energy

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  1. Ohm’s Law, Power and Energy EE 2010: Fundamentals of Electric Circuits Mujahed AlDhaifallah

  2. Ohm’s Law! • Current flows because Electrons flow from one point to another. • What causes the flow of electrons?

  3. Ohm’s Law! • Current flows because Electrons flow from one point to another. • What causes the flow of electrons? • Voltage (potential difference)

  4. Ohm’s Law! • Current flows because Electrons flow from one point to another. • What causes the flow of electrons? • Voltage (potential difference) • More voltage results in more or less electrons?

  5. Ohm’s Law! • Current flows because Electrons flow from one point to another. • What causes the flow of electrons? • Voltage (potential difference) • More voltage results in more or less electrons? • More electrons

  6. Ohm’s Law! • So does that mean that Current is proportional to Voltage?

  7. Ohm’s Law! • So does that mean that Current is proportional to Voltage? • Yes • The more the voltage the more is the current

  8. Ohm’s Law • What is the effect of resistance?

  9. Ohm’s Law • What is the effect of resistance? • Do more electrons flow when there is a high resistance?

  10. Ohm’s Law • What is the effect of resistance? • Do more electrons flow when there is a high resistance? • No

  11. Ohm’s Law • What is the effect of resistance? • Do more electrons flow when there is a high resistance? • No • The higher the resistance, the less is the current.

  12. Ohm’s Law • What is the effect of resistance? • Do more electrons flow when there is a high resistance? • No • The higher the resistance, the less is the current. • Current is inversely proportional to the resistance.

  13. Ohm’s Law • I = V/R • V=IR • R=V/I

  14. Ohm’s Law • An element with R = 0 is called a short circuit, as for a short circuit, v = iR = 0, current could be any value. • an element with R =∞ is known as an open circuit for an open circuit, i =v/R =0, voltage could be any value

  15. Question • In the circuit shown, calculate the current i.

  16. Power • Power dissipated by charge flowing through a resistor • P = VI • P = V2/R • P = I2R

  17. Question • In the circuit shown, calculate the power p.

  18. Energy • Energy = Power x Time

  19. Question • How much energy (in kilowatthours) is required tolight a 60-W bulb continuously for 1 year (365 days)?

  20. Devices EE 2010: Fundamentals of Electric Circuits Mujahed AlDhaifallah

  21. Battery • Chemical Reactions to produce potential difference • Alkaline and lithium-iodine primary cells • Lead Acid secondary cell • Nickel-Cadmium Secondary cell • Nickel-Hydrogen and Nickel-Metal Hydride Secondary cells • Solar Cells

  22. Power Supply • Used very frequently in all devices. • Transform the AC supply into a lower voltage • Rectify it (?)

  23. Independent voltage source • provides a specified voltage • (independent of the current through the element)

  24. Independent Current Sources • Supplies a fixed amount of current • It is the dual of the battery • In a battery voltage is constant, but current drains out

  25. Dependent source • is a voltage or current generator whose source quantity depends on another circuit variable (current or voltage)

  26. Dependent source • There are four types of dependent sources: • VCVS, VCCS, CCVS, CCCS • Vx: controlling voltage • Ix: controlling current

  27. Example • Compute the power that is absorbed or supplied by the elements in the following network.

  28. Ammeters • Device to measure current • The wire in which current is to be measured is broken up, and are joined via an ammeter. • What should be the resistance of the ammeter?

  29. Voltmeters • Devices to measure voltage • Connected in a parallel fashion across the device where there is a need to measure potential difference. • What should be the resistance of a voltmeter?

  30. Ohmmeters • Used to measure the resistance of a device. • Connected across the two pins of a resistor • Also used to check the continuity of networks.

  31. Wattmeters • Used to measure the dissipation of power in a circuit element. • Includes both an ammeter and a voltmeter. • Displays the multiplication of both measurements.

  32. Fuses and Circuit Breakers • The power supply to the homes is not ideal. • If it goes above a specified level, it can burn the devices. May result in Fire or Smoke. • Fuse wires melt if they experience a large current. • In a breaker, a large current results in a large enough strength in an inbuilt electromagnet to draw the switch open

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