electricity and ohm's law

Electricity Basic electrical instruments and symbols; Electric charge and electric field; Current,

Resistance, and EMF; Circuits

Electric charge and Electric field

Field Type Caused By

gravity mass

electric charge

Electric charge and Electric field

Charge is not created

or destroyed, it is only

transferred.

Conductors and Insulators

transfers charge on

contact

does not transfer charge on contact

Charging ProcessesBy contact

PolarizationInduction

Coulomb’s law

The magnitude of the electric force between two point charges is directly proportional to the product of the

charges and inversely proportional to the square of the distance between them

Example

Two point charges, q1= +25nC and q2= -75nC, are separated by a distance of 3.0cm. Find the magnitude and direction of a) the electric force that q1 exerts on q2 b) and the electric force that q2 exerts on q1.

Current, Resistance, and EMF

CurrentIs any motion of charge from one region to

another

http://i01.i.aliimg.com/photo/v1/625092455/P01003_EDM_DC_AMMETER.jpg

Current, Resistance, and EMF

ResistanceRatio of V to I for a particular

conductor

(Ohm)R=V/I

Current, Resistance, and EMF

The influence that makes current flow

from lower to higher potential

Electromotive force or emf

(E)V=E=IR

http://i00.i.aliimg.com/img/pb/218/818/276/276818218_834.jpg

Current, Resistance, and EMF

Series

• It=I1=I2=I3

• Vt=V1+V2+V3+…

• Rt=R1+R2+R3+…

Parallel

• It=I1+I2+I3

• Vt=V1=V2=V3

• 1/Rt=1/R1+1/R2+1/R3

Retrieved from http://web.physics.ucsb.edu/~lecturedemonstrations/digital%20photos/light%20bulbs,%20series%20&%20parallel.jpg

Example

Calculate the voltage, current, and resistance across each resistor for each connections. For the second diagram, R1= R2= 4Ω and potential difference is 100V.

Retrieved fromhttps://learn.sparkfun.com/tutorials/series-and-parallel-circuits

Retrieved fromhttps://learn.sparkfun.com/tutorials/series-and-parallel-circuits

ELECTRIC POWEREnergy consumption

Electric power

• It is the amount of electrical energy one uses up per second

• SI unit is Watt• 1hp= 746 Watts

𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑝𝑜𝑤𝑒𝑟=𝑤𝑜𝑟𝑘𝑑𝑜𝑛𝑒

𝑡𝑖𝑚𝑒

Examples

• A man lifted a load of 80kg to a height of 1.5m in 3 seconds. What is the power in watts?

• A horse pulled a load with a force of 200N through a distance of 100m in 20 seconds. What is the power of the horse?

Energy cost

𝑐𝑜𝑠𝑡=𝑡𝑜𝑡𝑎𝑙𝑒𝑛𝑒𝑟𝑔𝑦 𝑢𝑠𝑒𝑑 𝑥𝑟𝑎𝑡𝑒

h𝑘𝑊

Example

A 1.5hp air-conditioning unit is used for 10h. How much electrical energy (work) did it consume? If the electric company charges 5.50 per kilowatt-hour (kWh), how much does the energy consumed cost?