Converting dc to ac. An individual cell such as an egg cell (an ovum, produced in the ovaries) is commonly organized spatially, as manifested in part by asymmetries in the cell membrane These asymmetries include non-uniform distributions of ion transport mechanisms, which result in a net
These cellular currents move in loops through extracellular fluid Ohm s law requires that there be a voltage difference between any two points in this current-carrying fluid surrounding cells Although the currents may be significant, the extracellular voltage differences are tiny—on the order of nanovolts If we can map the voltage differences in the fluid outside a cell, we can calculate the current density by using Ohm s law, assuming that the resistivity of the fluid is known We cannot measure these voltage differences by spacing two electrodes 10 or 20 μm apart because the dc impedance (the resistance) of such electrodes is high and the inherent noise in signals detected at the electrodes far exceeds the cellular voltages.
One successful method of measurement uses an electrode with a ball-shaped end made of platinum that is moved sinusoidally between two points in the fluid outside a cell The electric potential that the electrode measures, with respect to a distant reference electrode, also vanes sinusoidally The dc potential difference between the two extremes (the two points in the fluid) is then converted to a sine-wave ac potential difference The platinum electrode behaves as a capacitor in series with the resistance of the extracellular fluid This resistance, called the access resistance (RA), has a value of about ρ/10a, where ρ is the resistivity of the fluid (usually expressed in ω cm) and a is the radius of the ball electrode The platinum ball typically has a diameter of 20 pm and a capacitance of 10 μm; the resistivity of many biological fluids is 100 ω cm.
42 The signal from the oscillating electrode is fed into an amplifier, which reports the measured voltage as an rms value. 1.5 nV What is the potential difference between the two extremes?
- A. 1.5 nV
- B. 3 0 nV
- C. 2.1 nV
- D. 4 2 nV
Want to see the full answer?
Check out a sample textbook solutionChapter 22 Solutions
COLLEGE PHYS. VOL 1 LLF W/MODMAST >IC<
Additional Science Textbook Solutions
Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)
Physics for Scientists and Engineers: A Strategic Approach, Vol. 1 (Chs 1-21) (4th Edition)
The Cosmic Perspective Fundamentals (2nd Edition)
Introduction to Electrodynamics
Essential University Physics (3rd Edition)
Applied Physics (11th Edition)
- In an oscillating RLC circuit, R = 7.0 L. = 10 mH. And C = 3.0 F. Initially, the capacitor has a charge of 8.0 C and the current is zero. Calculate the charge on the capacitor (a) five cycles later and (b) 50 cycles later.arrow_forwardAn inductor and a resistor are connected in series across an AC generator, as shown in Figure CQ21.16. Immediately after the switch is closed, which of the following statements is true? (a) The current is V/R. (b) The voltage across the inductor is zero. (c) The current in the circuit is zero. (d) The voltage across the resistor is V. (e) The voltage across the inductor is half its maximum value. Figure CQ21.16arrow_forwardAn inductor and a resistor are connected in series across an AC generator, as shown in Figure CQ21.16. Immediately after the switch is closed, which of the following statements is true? (a) The current is V/R. (b) The voltage across the inductor is zero. (c) The current in the circuit is zero. (d) The voltage across the resistor is V. (e) The voltage across the inductor is half its maximum value. Figure CQ21.16arrow_forward
- A series RLCcircuit contains a 20.0- resistor, a 0.750-F capacitor, and a 120-mH inductor. (i) 11 a sinusoidally varying rms voltage of 120 V at f = 500 Hz is applied across this combination of elements, what is the rms current in the circuit? (a) 2.33 A (b) 6.00 A (c) 10.0 A (d) 17.0 A (e) none of those answers (ii) What If? W hat is the rms current in the circuit when operating at its resonance frequency? Choose from the same possibilities as in part (i).arrow_forward(a) At what two times in the first period following t = 0 does the instantaneous voltage in 60-Hz AC equal Vrms ? (b) V rms?arrow_forwardA precision laboratory resistor is made of a coil of wire 1.50 cm in diameter and 4.00 cm long, and it has 500 turns. (a) What is its self-inductance? (b) What average emf is induced it the 12.0 A current through it is turned on in 5.00 ms (one-fourth of a cycle for 50 Hz AC)? (c) What is its inductance if it is shortened to half its length and counter-wound (two layers of 250 turns in opposite directions)?arrow_forward
- In a purely inductive AC circuit as shown in Figure P21.15, Vmax = 100. V. (a) The maximum current is 7.50 A at 50.0 Hz. Calculate the inductance L. (b) At what angular frequency is the maximum current 2.50A? Figure p21.15arrow_forwardAn LC circuit in an AM tuner (in a car stereo) uses a coil with an inductance of 2.5 mH and a variable capacitor. If the natural frequency of the circuit is to be adjustable over the range 540 to 1600 kHz (the AM broadcast band), that range of capacitance is required?arrow_forwardAn ac source of voltage amplitude 10 V delivers electric energy at a rate of 0.80 W when its current output is 2.5 A. What is the phase angle between the emf and the current?arrow_forward
- Physics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781285737027Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning
- Physics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage LearningCollege PhysicsPhysicsISBN:9781938168000Author:Paul Peter Urone, Roger HinrichsPublisher:OpenStax CollegePrinciples of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning