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. What causes the flow of electrons?  Voltage (potential difference)

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?

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

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

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

Ohm’s Law What is the effect of resistance?

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

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

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.

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.

Ohm’s Law I = V/R V=IR R=V/I

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

Question In the circuit shown, calculate the current i.

Power Power dissipated by charge flowing through a resistor  P = VI  P = V 2 /R  P = I 2 R

Question In the circuit shown, calculate the power p.

Energy Energy = Power x Time

Question How much energy (in kilowatthours) is required to light a 60-W bulb continuously for 1 year (365 days)?

Devices EE 2010: Fundamentals of Electric Circuits Mujahed AlDhaifallah

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

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

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

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

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

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

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

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?

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?

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.

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.

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