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Ohm’s law and power

Ohm’s law and power. Ohm’s Law. For a given resistance, the potential difference is directly proportional to the intensity of the current.

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Ohm’s law and power

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  1. Ohm’s law and power

  2. Ohm’s Law • For a given resistance, the potential difference is directly proportional to the intensity of the current. • Ohm’s law establishes that for a given resistance the potential difference in an electrical circuit is directly proportional to the intensity of the current. • V = RI V represents the potential difference R represents the resistance (in Ω) I represents the intensity of the current

  3. Example Problem: • A nine volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing through the curling iron? • Sketch:

  4. Solution: • Know: V = 9 V R = 18 ohms Solve for I: I = V R I = 9 V = 0.5 A 18 ohms

  5. Electrical Power • The electrical power of an appliance is an indication of the quantity of work that it can do, the quantity of energy that it can transform in a certain period of time. • The unit of measure of electrical power is the Watt (W). An appliance with a power of one Watt does work of 1joule per second: • 1 W = 1J 1 s

  6. The mathematical equation of electrical power is • Pe = WPe represents the electrical power (in W) Δt W represents the work (in J) Δt represents the time required (in s)

  7. Pe = VIPe represents the electrical power (in W) V represents the potential difference (in V) I represents the intensity of the current (in A) • 1 W = 1V * 1A • = 1J * 1C C s • = 1 J s

  8. The relationship between Power and electrical energy • It is possible to determine the quantity of electrical energy consumed by an appliance by multiplying its power by time: • 1 W * 1 s = 1 J * 1 s s • = 1 J

  9. Electrical energy can be measured in joules but it can also be expressed in kilowatt hours (kWh) • 1 kWh = 1000 W * 3600 s = 3 600 000 J • The kilowatt hour is used in the calculation of bills of consumption of electricity.

  10. The following mathematical formula establishes the relationship between electrical energy and electrical power. • E= PeΔt E represents electrical energy consumed (in J or kWh) Pe represents electrical power (in W or kW) Δt represents the interval of time (in s or h)

  11. For example, if we use a 1000 W microwave oven for 6 minutes, the quantity of energy consumed would be: • E= PeΔt E= PeΔt • = 1000 W * 360s = 1 kW * 0.1 h • = 360 000 J = 0.1 kWh • The microwave oven would have consumed 360 000 J after six minutes of use or 0.1 kWh.

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