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Test Prep Splash

AlphaGeek

Entry posted by AlphaGeek

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Hi everyone, just figured that I'd post an accumulation of what I've been studying for the test tomorrow morning. It goes in video order because that's the order that I learned the material in. If something is too vague, I reccomed looking at the video for elaboration :)

Circuits

  1. Current and Current Density
  2. Resistors and Resistance
  3. Circuits
  4. Voltmeters and Ammeters
  5. Ideal and Real Batteries
  6. RC Circuits: Steady State
  7. RC Circuits: Transient Analysis (Charging)

Current and Current Density:

Current measured in Amps, or charge per sec.

An electric field is applied to a conductor and a small field is created that opposes it

Avg. Velocity of electrons in that field= drift velocity (Vd)

Vol= Bh = Vd * change in time * Area

# electrons = Volume * volume density(AKA "N")= N *change in time* Vd * Area

I= N*q*Vd *A

Current density = J* N*q*Vd

I= integral (J * dA)

J= I/A

Resistance ("Howdy, Y'all!" made my day in that vid, btw)

R=V/I

p = row =resistivity

R= pL/A

V= IpL/A

E=energy=V/L = p (I/A) = pJ

W=qV

I= dQ/dt

P=IV=I2R=V2/R

Circuits:

Series: Req= R1 +R2...

Parallel: 1/Req= 1/R1 +1/R2....

Kirchhoff's Current Law= sum all current entering = sum all current exiting (conserv. charge)

Kirchhoff's Voltage Law= sum of all potential drops in a closed loop of a circuit = 0 (conserv. energy)

Voltmeters and Ammeters:

Voltmeters: measures v between two points, high resistance, connected in parallel

Ammeters: measures current, low resistance, connected in series

Ideal and Real Batteries:

Ideal: no internal resistance

V battery = Emf = change in V

Real: has internal resistance

V battery = change in V = IR = Emf- (I)®, where r = internal resistance

For battery:

W= change in Q * Emf

P= W/change in time = (change in Q)(Emf)/(change in time)

P resistor (works for both external and internal) = I2R

RC Steady State:

series: 1/Ceq= 1/C1 + 1/C2 ...

Parallel: Ceq = C1+C2...

RC Charging:

W= I2R

U=1/2 C V2

Time constant Tao=RC, occurs when quantity is 63% of its final value. 5 Tao= 99% final value (practically final value)

Note: an uncharged capacitor acts like a wire, a charged capacitor acts like a gap in the circuit (AKA no current)

...Okay, bed time. Good luck tomorrow, everyone!

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