10 Electrical Ciruits Flashcards
Kirchhoff’ s first law
Current into a junction = current out
Kichhoff’s second law
In an circuit the sum of the electromotive force is equal to the sum of the potential differences around a closed loop
Kirchhoff’s laws in series
The current is the same in every component
Potential difference is shared proportionally between components based on resistance big R -> big V
Kirchhoff’s laws in parallel
Current is shared proportionally between components based on resistance big R -> small I
EMF is equal to the potential difference in each component
Rt in series
R1 + R2+ …
Vt in series
V1 + V2 + …
Rt in parallel
1/Rt = 1/R1 + 1/R2 + …
It in parallel
I1 + I2 + …
What the the four important equations for analysing circuits
Q = It
W = VQ
P = IV
V = IR
Lost volts = Epsilon - V
Lost volts = EMF - terminal pd
How does current effect lost volts
As current increases lost volts increases as current decreases lost volts decreases
Lost volts = Ir
Lost volts = current x internal resistance
Epsilon = I(R + r)
EMF = current ( resistance + internal resistance)
How can varying potential difference be achieved
Using a potential divider and a variable resistor
Potentiometer
A variable resistor with three terminals and a sliding contact. Used in low voltage electrical circuits
