1 / 14

Electrical Calculations

Electrical Calculations. A German school teacher Georg Ohm studied the resistances of materials, and measured the current resulted from different voltages applied to a piece of metal wire. He found the relationship between: The current versus the resistance at constant voltage

herb
Download Presentation

Electrical Calculations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electrical Calculations

  2. A German school teacher Georg Ohm studied the resistances of materials, and measured the current resulted from different voltages applied to a piece of metal wire. • He found the relationship between: • The current versus the resistance at constant voltage • The current versus Voltage in a specific resistance.

  3. Ohm’s Law: • The ratio of voltage (V) to current (I) is a constant for each material. • This Ratio is equal to the resistance (R) of materials. R= or V= I  R • Units used: Voltage is expressed in volts (V) , current is expressed in amperes (A), Resistance is expressed in ohms (Ω) .

  4. Ohm’s Law: • The relationship between current, voltage and resistance: Inversely proportional Directly proportional

  5. Problems on using Ohm’s law: Problem 1: What is the voltage needed to make a current of 3 A in a resistance of 9Ω? Answer: V= I  R V= 3 A  9 Ω= 27 V

  6. Problems on using Ohm’s law: Problem 2: What is the current that results from applying 10 V in the presence of a resistance of 2 Ω? Answer: I = V R I = 10 V = 5 A 2 Ω

  7. Electric power: is the rate at which electrical energy is changed into other forms of energy. • The unit is watt (W), and the symbol for power in equations is (P). Power= Voltage  current P = V  I Another unit of power is kW “Kilowatt”. kW = 1000 W

  8. Electrical calculations: Problem 3: What is the power for a television that draws a current of 0.42 A at 120 V? Answer: P= V  I P= 120 V  0.42 A = 50.4 W

  9. Electrical calculations: Problem 4: A car uses a 12V battery. One headlight draws about 3A. What is the power of the headlight? Answer: P= V  I P= 12 V  3 A = 36 W

  10. Measuring Electrical energy: Electric power companies keep track “recording” of how much electrical energy a household or business uses. This is done using electric meter. The amount of electrical energy depends on the electrical power used and the length of time. Electrical energy = power  time E (kWh) = P (kW)  t (h)

  11. Electrical calculations: Problem 5: A small television set draws a current of 0.42A at 120V. What is the power rating for the television? How much energy is used if the television is on for 3 hours? Answer: P= V  I = 120  0.42 = 50.4 W = 0.0504 kW E= P  t = 0.0504  3 = 0.1512 kWh

  12. Electrical calculations: Problem 6: How much electrical energy does a 100 W light bulb use if it is left on for 24 h? Answer: E= P  t E= 0.1 kW  24 h = 2.4 kWh

  13. How to save energy: • Replacing items that have high power ratings with items that have low power ratings. • Turning off lights and instruments when they are not in use.

More Related