1. Kashif Bashir1 mailto: Kashifbm@msn.comKashifbm@msn.com Web: kashifpaf.greatnow.comkashifpaf.greatnow.com OHM’s LAW

2. Kashif Bashir2 The Current I = V/R Current is directly Proportion to Voltage at constant Resistance. Or If we Keep the same resistance in a circuit but vary the voltage, the current will vary. V  I (cost. R) V=IR I = V/R Amperes = volts/ohms

3. Kashif Bashir3 Examples A heater with a resistance of 8  is connected across the 120 v power line. How much is the current I ? I = V/R = 120/8 = 15A A small light bulb with a resistance of 2400  is connected across the same 120v power line. How much is the current I? I = V/R = 120/2400 = 0.05 A

4. Kashif Bashir4 The Voltage V= IR Voltage is directly proportional to resistance at constant current or The voltage across R must be the same as the source V b/c the resistance is connected directly across the battery. V  R (const. I) V= IR. 1 volt = 1 ampere x 1 ohm

5. Kashif Bashir5 The Resistance R = V/I Resistance is inversely proportional to current at constant voltage. R  1/I (const V) R= V/I 1 ohm = 1 volt / 1 ampere Example: The I of 8 mA flows through a 5-k  R. How much is the IR voltage? v = IR = 8 x 10 -3 x 5 x 10 3 = 40 v

6. Kashif Bashir6 The Linear Proportion b/w V and I

7. Kashif Bashir7 Electric Power One watt of power equals the work done in one second by the volt of potential difference in moving one coulomb of charge. Or Power in watt equals the product of volts times amperes. 1. P = V x I 2. P =V 2 / R 3. P = I 2 R Work and energy are essentially the same with identical unit. Power is different. However, b/c it is the time rate of doing work.

8. Kashif Bashir8 Electric Power Continue Watt and horsepower units 746 w = 1 hp =550 ft – lb/s 1 ev (electron volt) is the amount of work required to move an electron b/w two points that have a potential difference of one volt The number of electron volts equal to one joule must be 6.25 x 10 18 Kilowatthours is a unit commonly used for large amounts of electrical work or energy. If a light bulb used 300W or 0.3 Kw for 4 hours, the amount of energy is 0.3 x 4, which is 1.2 kWh.

9. Kashif Bashir9 Open And Short Circuit Troubles