Flashcards in Chapter 23 Deck (14):
What is Kirchhoff's Junction Law?
Is a result of conservation of current
I1 = I2 + I3
ΣIn = ΣOut
What is Kirchhoff's Loop Law?
states that the sum of the potential differences around any loop formed by a circuit can must be zero.
ΔVloop = ΣΔVi = 0
What are Kirchhoff's Loop Law Conventions?
- When traveling through a battery from the - to + terminals (up the ski lift), the potential increases ΔV = +V
- When traveling thought a battery from the + to - terminals (down the ski lift), the potential decreases ΔV= -V
What are Kirchhoff's Loop Laws that apply to Resistors?
- When travelling through a resistor IN the direction of current (ski downhill), the potential decreases ΔV= -IR
- When travelling through a resistor AGAINST the current, (ski uphill) the potential increases ΔV = IR
What is the difference between an Ideal Battery?
Ideal Battery: ΔVtot = +V
Real Battery: ΔVtot = V - IR
What are RC Circuits?
- RC Circuits are circuits containing resistors and capacitors
- In RC Circuits the current varies with time
- The values in RC circuits determine the time it takes the capacitor to charge or discharge
What happens Before the Switch Closes for Discharging Capacitors?
before the switch closes, in a state of equilibrium
Vo = Qo/C
Io = Vo/R = Qo/RC
- As time goes on the charge on the capacitor decreases, and thus so does the potential energy and current
What happens Immediately After the Switch Closes for Discharging Capacitors?
The charge separation on the capacitor produces a potential difference, which causes a current
- The current is the flow of charge, the current discharges the capacitor
What happens At a Later Time for Discharging Capacitors?
The current has reduced the charge on the capacitor. This reduces the potential difference, the reduced potential difference leads to a reduced current
I = Ioe^-t/RC
V = Voe^-t/RC
V = V(1 - e^-t/RC)
Discharging Capacitors Exponentially?
After the switch closes at time (t = 0), the current and voltage decay to zero EXPONENTIALLY
What is a time constant (τ)?
τ = RC
- Is a characteristic time for a circuit
- A long time constant implies, slow decay. A short time constant implies a rapid decay
What Happens when the time increases by (τ)?
When the time increases by τ, the voltage and current decrease by a factor of e^-1 = 0.37
Action Potential: What Happens when a cell depolarizes?
A cell depolarizes when a stimulus causes the opening of sodium channels, the rapid influx of sodium ions into the cell, cause the charge inside to become excessively positive like 40mV, then the channels close.