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Ohm’s Law

Ohm’s Law. How voltage, current, and resistance relate. Ohm’s Law. Current through an ideal conductor is proportional to the applied voltage Conductor is also known as a resistor An ideal conductor is a material whose resistance does not change with temperature For an ohmic device,

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Ohm’s Law

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  1. Ohm’s Law How voltage, current, and resistance relate

  2. Ohm’s Law Current through an ideal conductor is proportional to the applied voltage • Conductor is also known as a resistor • An ideal conductor is a material whose resistance does not change with temperature For an ohmic device, Voltage = Current x Resistance V = I x R • V = Voltage (Volts = V) • I = Current (Amperes = A) • R = Resistance (Ohms = Ω)

  3. Current and Voltage Defined Conventional Current: (the current in electrical circuits) Flow of current from positive terminal to the negative terminal. - has units of Amperes (A) and is measured using ammeters. Voltage: Energy or force required to move a charge from one point to another. - has units of Volts (V) and is measured using voltmeters. Resistance: Free electrons tend to move through conductors with some degree of friction, or opposition to motion Think of voltage as what pushes the electrons along in the circuit, and current as a group of electrons that are constantly trying to reach a state of equilibrium.

  4. Here are the standard units of measurement for electrical current, voltage, and resistance:

  5. In circuit below, there is only one source of voltage (the battery, on the left) and only one source of resistance to current (the lamp, on the right). This makes it very easy to apply Ohm's Law. If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third. • In this first example, we will calculate the amount of current (I) in a circuit, given values of voltage (E) and resistance (R):

  6. In this first example, we will calculate the amount of current (I) in a circuit, given values of voltage (E) and resistance (R):

  7. What is the amount of current (I) in this circuit? • V = I * R • I = V/R • I = 12/3 • I = 4 Amps

  8. Calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I):

  9. What is the amount of resistance (R) offered by the lamp? • V= I * R • R = V/I • R = 36/4 • R = 9 

  10. Calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R):

  11. What is the amount of voltage provided by the battery? • V = I x R • V = (2A)(7Ω) • V = 14 V V = I x R = (2A)(7Ω) = 14 V

  12. V I R • Trick to remember how to solve.

  13. V I R • If you know E and I, and wish to determine R, just eliminate R from the picture and see what's left: R = V/I

  14. V I R If you know E and R, and wish to determine I, eliminate I and see what's left: I = V/R

  15. V I R Lastly, if you know I and R, and wish to determine E, eliminate E and see what's left: V = IxR

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