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Category: Electromagnetic Theory
Type: Lecture Notes
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axoplasm
semipermeable, battery, resistor,
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Description
Physics for Bioscience (II)
Transcript
Administration
RC Circuits in Neurons
An RC time constant determines the speed at which nerve impulses travel
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Second level
Third level
Fourth level
Fifth level
Instructor
Franco Gaspari
PHY 1040U
(Physics for the biosciences)
Introduction to Electromagnetism and Optics
Lecture 14
March 06, 2007
1. A battery has an emf of 15.0 V. The terminal voltage of the battery is 11.6 V when it is delivering 20.0 W of power to an external load resistor R. (a) What is the value of R (b) What is the internal resistance of the battery
6. (a) Find the equivalent resistance between points a and b in the Figure. (b) A potential difference of 34.0 V is applied between points a and b. Calculate the current in each resistor.
2
The Ammeter and the Voltmeter
R for ammeters is very small.
R for voltmeters is very large.
I1
I2
R1
R2
Why
The current passes directly through the ammeter.
Since the resistance of the ammeter is in series, then
We place the voltmeter between the 2 terminals of a resistor to measure the potential drop.
However, with the voltmeter connected, in reality we measure
RC Circuits
(a) A capacitor in series with a resistor, switch, and battery. (b) Circuit diagram representing this system at time t 0, before the switch is closed. (c) Circuit diagram at time t 0, after the switch has been closed.
Charging a Capacitor
Discharging a Capacitor
Analyze qualitatively the behavior of the current in the circuit below
just after the switch is closed
a long time after the switch is closed.
Flashing Lamp
A fluorescent lamp L is connected in parallel with C.
There is a current through the lamp only when the potential difference across it reaches a breakdown voltage VL.
When V VL the capacitor discharges through the lamp.
We want 2 flashes per second.
The time it takes for the voltage to reach VL is given by
0
Myelin sheath
Axoplasm
Semipermeable membrane
Simplified Model of Myelinated Axon
Myelin sheath
Axoplasm
Semipermeable membrane
Myelin sheath
Axoplasm
Semipermeable membrane
Myelin sheath
Axoplasm
Semipermeable membrane
An estimate of how fast the electrical impulse travels is
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