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DC Circuits - Coggle Diagram
DC Circuits
More Circuit
Calculations
Circuit: 1 Cell, multiple resistors
Cell = ε/R(T), cell emf divded by total circuit R
Component Pd = current * spec. R
Current through each resistor = Total p.d. / spec. R
Circuit: Cells in Series
current = net emf / total resistance
Same direction cells - net emf = sum of emfs
opposed cells - net emf = difference of emfs
Circuit: Identical Cells in Parallel
n identical cells, individual current = I / n
Spec. Terminal V = e - Ir / n (e- only chooses one path)
Circuit: Diodes
given p.d. exists across diode in forward-bias
(Near) Infinite resistance in reverse-bias
Kirchhoff's Laws
At any circuit junction, total current in = total out
For any circuit loop, sum of emfs = sum of potential drops
Potential
Divider
Theory
Potential Divider - multiple resistors in series
Source w/ fixed p.d, divided between components
PD can be used to supply p.d. fixed at an V
PD can supply variable pd or pd dependent on temp/PSI
For fixed potential difference
R = R1 + R2, I = V(T) / R >>> I = V(T) / R1 + R2
V1 = IR1 = R1 * V(T) / R1 + R2 >>> R1 % * V(T)
P.d. ratio of 2 resistors equals resistance ratio of 2 resistors
For variable potential difference
Source pd connected to uniform resistance wire/track
sliding contact moved along wire, many uses:
- Simple audio volume control for speaker,
audio signal supplied to PD, variable output to speaker
- Variable light switch, potential difference can reach zero
unlike w/ variable resistor, still a current thru bulb at max R
Sensor Circuits
Temperature Sensor - has PD of a thermistor and VarR
Adjusting VarR, adjusts desired pd across thermistor
Temp change = thermistor change = R change
pd divided between thermistor and VarR
Light Sensor - Light-dependent resistor (LDR) instead
of Thermistor, varies with light intensity (inversely)
More about
Resistors
Resistor in Series
V = V1 + V2 >>> IR = IR1 + IR2
IR = I * (R1 + R2) >>> R = R1 + R2
Total resistance = sum of individual resistances
R = R1 + R2 + R3 + ...
Resistor in Parallel
I = I1 + I2 >>> V/R = V/R1 + V/R2
V/R = V * (1/R1 + 1/R2) >>> 1/R = 1/R1 + 1/R2
1/R = 1/R1 + 1/R2 + 1R3 + ...
Resistance Heating
Heating effect of e-current due to component resistance
Charge carriers collisions, net transfer of KE to heat
P = IV, V = IR >>> P = I^2R, rate of heat transfer
Temp. rise depends on power supplied and heat trans. rate
to surroundings; energy trans. to obj, E = Pt
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Circuit Rules
Current Rules
Junction Rule - At any circuit junction,
total current leaving equals total current entering,
rates of charge flowing in/out of a junction always equal
Components in Series - current entering component
equals current leaving, components don't use up current
Current passing thru components in series doesn't change
Potential Difference Rules
Potential Difference (p.d.) - energy transfer per coulomb
Charge carriers lose energy >>> p.d. = potential drop
Charge carriers gain energy >>> p.d. = potential rise
Components in Series - total p.d. across all components
= sum of p.d. difference across each component
Components in Parallel - p.d. across components are equal
Complete Circuit Loop - sum of emfs = sum of potential drops