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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?