Physiology 3140A Lecture Notes - Lecture 1: Electric Field, Lipid Bilayer, Potassium Channel

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16 Oct 2011

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Electric potential - - the electric potential (electrostatic potential) at a point in space is the electrical potential energy divided by charge at is associated with the static electric field. Measured in volts electric field exerts a force on charged objects, accelerating them in the direction of the force. In the same or opposite direction of the electric field if the object has a positive charge the force and acceleration will be in the direction of the field. Measured in amperes (charge flowing at one coulomb per second) Measured in ohms resistance is measured as the proportion of voltage to current (r = v/i) Capacitance - - the ability of a body to hold an electric charge; its also a measure of the amount of electrical energy stored (or separated) for a given electrical potential. Potential (volts) mv (10-3 v), uv (10-6 v) Current (amperes) na (10-9 a), pa (10-12 a) Resistance (ohms) - m (10^6 ), g (10^9 )

Related Questions

1.Two uncharged, conducting spheres, A and B, are held at rest oninsulating stands and are in contact. A positively charged rod isbrought near sphere A. While the rod is in place, the two spheresare separated. How will the spheres be charged, if at all, afterthey are separated?
Sphere A Sphere B
(a) positive positive
(b) positive negative
(c) negative positive
(d) negative negative
(e) zero zero

2. A charged conductor is brought near an uncharged insulator.Which one of the following statements is true?
(a) Both objects will repel each other.
(b) Both objects will attract each other.
(c) Neither object exerts an electrical force on the other.
(d) The objects will repel each other only if the conductor has anegative charge.
(e) The objects will attract each other only if the conductor has apositive charge.

3. An electron is moved from point A, where the electric potentialis VA = â240 V, to point B, where the electric potential is VB =â360 V. What is the change in the electric
potential energy?
(a) 1.92Ã10â17 J (b) 2.04Ã10â17 J (c) 5.75Ã10â17 J (d) 8.98Ã10â17 J(e) 1.05Ã10â16 J

4. A -2q charge is located a distance d to the right of a +4qcharge, along the x
axis. At which point (or points) along the axis does the electricfield go to zero? To
solve this problem, consider an observer at point P, which is anarbitrary distance x from the +4q charge. Find the value (orvalues) for x (in terms of the separation distance d) where thetotal electric field vanishes.
(a) The electric field is never zero in the vicinity of thesecharges.
(b) The electric field is zero at x = -0.328d.
(c) The electric field is zero at x = +4.22d.
(d) The electric field is zero at both x = -2.26d and x =+2.26d.
(e) The electric field is zero at x = +3.41d.

5. point A is a distance L away from a point charge Q. Point B is adistance 4L away from Q. What is the ratio of the electrostaticpotential at B to that at A, i.e., what is VB/VA?
(a) 1/16
(b) 1/9
(c) 1/4
(d) 1/3
(e) can not be determined without specifying Q and L

6. Which one of the following statements best explains why it ispossible to define an electric potential
in a region of space that contains an electric field?
(a) Work must be done to bring two positive charges closertogether.
(b) Like charges repel one another and unlike charges attract oneanother.
(c) A positive charge will gain kinetic energy as it approaches anegative charge.
(d) The work required to bring two charges together is independentof the path taken.
(e) A negative charge will gain kinetic energy as it moves awayfrom another negative charge.

Consider an electric dipole whose dipole moment (a vector pointing from the negative charge to the positive charge) is oriented at an angle with respect to the y-axis. There is an external electric field of magnitude E (independent of the field produced by the dipole) pointing in the positive y-direction. The positive and negative ends of the dipole have charges +q and -q, respectively, and the two charges are a distance d apart. The dipole has a moment of inertia I about its center of mass. It will help you to imagine that the dipole is free to rotate about a pivot through its center.

A) What is the net force that the dipole experiences due to the electric field?

B) What is , the magnitude of the torque that the electric field exerts about the center of mass of the dipole?

C) Using the above result, find the potential energy associated with the dipole's orientation in the field as a function of the angle shown in the figure. Take the zero of the potential to occur when the dipole is at angle ; that is , .

D) In terms of the dipole moment , What is the expression for the torque on a dipole in the field ?

E) In terms of the dipole moment, What is the expression for the potential energy of a dipole in the field?

redmammoth521

A conductor is placed in an external electrostatic field. The external field is uniform before the conductor is placed within it. The conductor is completely isolated from any source of current or charge.

Which of the following describes the electric field inside this conductor?

a) It is in the same direction as the original external field.
b) It is in the opposite direction from that of the original external field.
c) It has a direction determined entirely by the charge on its surface.
d) It is always zero.

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Physiology 3140A Lecture Notes - Lecture 1: Electric Field, Lipid Bilayer, Potassium Channel

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