Circuit Concepts

Temperature and Current - MIT TV

"Why does the bulb get brighter when the rod is put in the liquid nitrogen?"

"Lowering the temperature of a wire  reduces resistance and increases current"

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Fill-in the Blanks Notes

II. Circuit Concepts

Conservation of charge and energy for electric current

Gustav Robert Kirchhoff
(March 12, 1824 – October 17, 1887) was a German physicist

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1) Kirchhoff's 1st Law

“Amps In = Amps Out”

Ex 1)

 Amps In = Amps Out

Remember

 “Amps In =
 Amps Out”

Ex 2) Current in bottom branch?

Amps In = Amps Out

Ex 3)

Amps In = Amps Out

X = 16 amps

 

 

 

Ex 4)

 

 

 

Amps In = Amps Out

5 A + x = 15 A

 

x = 10 A IN

 

 

 

 

What's Wrong With This Picture?             Current In (10 A), does not equal current out (4 A)

 

 

 

 

 

 

 

2) Kirchhoff's 2nd Law - the algebraic sum of all the voltage drops and applied voltages around a circuit = 0

(conservation of energy)

 

 

Amount of PE gained when you go up a ski slope = energy released going down a ski slope 

(KE, Work against friction and snow)

 

 

 

 

 

Applied Voltage ( + )
Voltage Drop ( - )

 

0 =  12 V + -2 V + x + -6 V

 

0 = 12 V + -8 V + x

 

0 = 4 V + x

 

x = - 4 volts

 

 

VT = V1  + V2 + ...

 

 

 

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