RESISTANCE AND RESISTIVITY

1. Definition
   The resistance of a component is a measure of the opposition an electric current experiences when it flows through the component. The resistance (R) of a component is the ration of the potential difference (V) across it to the current (I) flowing through it.
   Aside from temperature, the resistance (R) of a conductor also depends on:
  • Its length
  • Its cross-sectional area (A) or thickness
  • The type of material it is made of

2. Formula
Resistance Formula
Where:
  • I stands for electric current (A)
  • V stands for the potential difference (Volt)
  • R stands for resistance (Ω)
Resistivity Formula
Where:
  • R stands for resistance (Ω)
  • ρ stands for resistivity (Ωm)
  • A stands for cross sectional area (m²)
  • L stands for length (m)
3. Important Figure
   Georg Ohm (1789-1854) was a German physicist, he is best known for his "Ohm's Law" which states that the current flow through a conductor is directly proportional to the potential difference (voltage) and inversely proportional to the resistance. After extensive research, he wrote "Die Galvanische Kette, Mathematisch Bearbeitet" (The Galvanic Circuit Investigated Mathematically) in 1827, which formulated the relationship between voltage (potential difference), current and resistance in an electrical circuit.

4. Uses in Everyday Life
 
   Resistors can be found in the electrical appliances that we use in daily life. The laptop charger has tens or hundreds of resistors controlling the current flow through different components, the mobile phone charger also shares this same function with the laptop charger. Resistors are also used inside of lightbulbs and street lighting, the electronic circuits in CFL, LED, and other lightbulbs contain resistors while automatic street lighting systems utilizes LDR (light dependent resistors) in their working.


Picture Sources:

http://www.physics4kids.com/files/elec_resistance.html

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html

https://www.autodesk.com/products/eagle/blog/how-choose-right-resistor/

https://en.wikipedia.org/wiki/Georg_Ohm

http://ohmlaw.com/practical-applications-of-resistors-in-daily-life/








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