PHYS115Exam2-GO back to #1 for electric field stuff (Module 7-

Which of the following statements is true about a cardiac myocyte in its resting state?

---Inside the cell the concentration of negative ions is higher than the concentration of positive ions. ---The value of the electric potential is lower inside the cell than outside.

Place several E-Field Sensors at a few points on different equipotential lines, and look at the relationship between the electric field and the equipotential lines. Which statement is true?

--At any point, the electric field is perpendicular to the equipotential line at that point, and it is directed toward lines of lower voltages. **All points on an equipotential line have the same voltage; thus, no work would be done in moving a test charge along an equipotential line. No work is done because the electric field, and thus the force on the test charge, is perpendicular to the displacement of the test charge being moved along the equipotential line.

Which statement best describes the distribution of the equipotential lines?

--The equipotential lines are closer together in regions where the electric field is stronger. **Near the positive charge, where the electric field is strong, the voltage lines are close to each other. Farther from the charge, the electric field is weaker and the lines are farther apart.

Now, remove the positive charge by dragging it back to the basket, and drag one negative charge toward the middle of the screen. Determine how the voltage is different from that of the positive charge. How does the voltage differ from that of the positive charge?

--The voltages become negative instead of positive and keep the same magnitudes. ***The voltage is still inversely proportional to the distance from the charge, but the voltage is negative everywhere rather than positive.

Which of the following are true about a voltmeter? Select all that apply.

--red wire is typically plugged into the positive terminal and a black wire is typically plugged into the negative terminal. --The voltmeter reports the potential difference between the positive and negative terminals.

Which of the following are true? Select all that apply.

-A positive charge speeds up as it moves from high to low electric potential. -A negative charge slows down as it moves from high to low electric potential.

Which of the following quantities will you reason about in part A? Select all that apply.

-electric potential difference -work -electric potential energy -kinetic energy

Mechanical energy is conserved in the presence of which of the following types of forces?

-magnetic -gravitational -electrostatic ***Gravitational, electrostatic, and magnetic forces are the only forces acting on the system involving the alpha particle, so the mechanical energy of the system is conserved. Note that in this problem you can ignore gravitational and magnetic forces because the electric force is much larger.

An alpha particle (α), which is the same as a helium-4 nucleus, is momentarily at rest in a region of space occupied by an electric field. The particle then begins to move. Find the speed of the alpha particle after it has moved through a potential difference of −3.45×10−3 V . The charge and the mass of an alpha particle are qα = 3.20×10−19 C and mα = 6.68×10−27 kg , respectively.Which of the following quantities are unknown?

-the value of the electric potential at the final -position of the alpha particle the final speed of the alpha particle -the value of the electric potential at the initial position of the alpha particle ***The unknown quantity that you have to find is the final speed of the alpha particle, (vf)α. Although you do not know the electric potential at the initial and final positions, you do know the difference between these values, ΔV=Vf−Vi= −3.45×10−3 V . Before you start creating the equation you will use to solve for (vf)α, first draw a before-and-after visual overview.

What was the initial kinetic energy of the electron, in electron volts?

1.02 V

By moving a 10 nC charge from point A to point B, you determine that the electric potential at B is 160 V .

160V

What is the voltage 3 m away from the charge?

3v ***Based on this result, and the previous question, the electric potential (voltage) is inversely proportional to the distance r from the charge: V∝1/r. Recall that the magnitude of the electric field E∝1/r2.

that is the largest number of bulbs contained in a circuit that you will reason about in this studio?

4

Using the voltage meter, you should find that 1 m away from the charge, the voltage is 9 V. What is the voltage 2 m away from the charge?

4.5 V ***Unlike the magnitude of the electric field, the electric potential (voltage) is not proportional to the inverse of the distance squared.

Figure 21.29 (p. 685) shows the placement of two electrodes (1 and 2) on a patient and the resulting electrocardiogram. Electrodes 1 and 2 are equivalent to the terminals on a voltmeter. In order to produce the electrocardiogram shown in Figure 21.29d, which electrode (1 or 2) would correspond to the positive terminal of a voltmeter?

Electrode 2

Which of the answers below best describes the activities in part C and D of the studio?

Making predictions and observations of currents in parallel circuits.

A charge q is placed near a group of source charges of total charge Q. Which of the following quantities does the electric potential experienced by q depend upon? Select all that apply.

Q q's location relative to the group of charges

What is the definition of current?

The amount of charge that flows through a cross-section of wire per unit time.

Which of the following statements is true? --The electric field strength is greatest where the voltage is the greatest. --The electric field strength is greatest where the voltage is the smallest. --The electric field strength is greatest where the equipotential lines are very close to each other.

The electric field strength is greatest where the equipotential lines are very close to each other. ***Locations where the voltage is changing steeply are locations with a strong electric field. The magnitude of the electric field is equal to the rate the voltage is changing with distance. Mathematically, this idea is conveyed by |Es|=dV/ds, where Es is the component of the electric field in the direction of a small displacement ds. (As you learned earlier, the electric field is directed in the direction where the voltage decreases.)

Which of the following is a true statement about equipotential lines.

The electric potential difference between two points on an equipotential line is 0 V.

Which statement is true about the dipole moment of the heart?

The heart only has a dipole moment while it is depolarizing.

It takes 4.0 μJ of work to move a 12 nC charge from point A to B. It takes -5.0 μJ of work to move the charge from C to B. What is the potential difference VC−VA?

VC−VA = 750 V

What apparatus will you use in part B of the studio?

Voltmeter

What is the voltage at the midpoint of the two charges?

__Exactly twice the voltage produced by only one of the charges at the same point **Because voltage is a scalar quantity, there are no vector components with opposite directions canceling out, as for electric fields. The voltage is simply the sum of the voltages due to each of the individual charges. Since both charges are positive, the voltage due to each charge (at all locations) is positive.

In this studio, the voltage difference is provided by:

batteries

In part B of the studio, in what form will the electrodes be provided to you?

carbon paper

Chose the word that correctly completes the following sentence: Kirchoff's junction law expresses the conservation of ____.

charge

As an electric field gets stronger, does the distance between equipotential lines increase, decrease, or stay the same?

decrease

Chose the correct word or phase to complete the following sentence: As you get closer to a negative point charge, its electric potential ______.

decreases

If I move in the direction that an electric field points, will I end up at a location that has a higher or lower electric potential than where I started?

lower

An electron with an initial speed of 6.00×105 m/s is brought to rest by an electric field. Did the electron move into a region of higher potential or lower potential?

region of lower potential

Now chose the option below that best completes this sentence: An ammeter is always connected in ____ because it has very ___ resistance.

series; low

What does a voltmeter measure?

the difference in the electric potential between two points

A particle with charge 8.00×10−19 C is placed on the x axis in a region where the electric potential due to other charges increases in the +x direction but does not change in the y or z direction. The particle, initially at rest, is acted upon only by the electric force and moves from point a to point b along the x axis, increasing its kinetic energy by 6.40×10−19 J . In what direction and through what potential difference Vb−Va does the particle move?

the particle moves to the left through a potential difference of Vb−Va= -0.800 V ***In general, if no forces other than the electric force act on a positively charged particle, the particle always moves toward a point at lower potential.

How many electrode configurations will each group analyze?

three

How many electrode configurations will each group measure?

two

What is the final velocity of the alpha particle, (vf)α?

vf)α = 575 m/s

Express your answer using the symbols for the units meters, seconds, kilograms, and coulombs.

volt = kgm^2/s^2C A volt is equivalent to a kg⋅m2/(C⋅s2). If you had known this before using the expression given here for (vf)α, you could have carried out a unit analysis to determine that your expression would give you the desired units of velocity (m/s). (CHECK mastering)

What is the voltage at the midpoint of the dipole?

zero ***Because the voltage due to the negative charge has the opposite sign of the voltage due to the positive charge at the midpoint, the net voltage is zero. The electric field, however, is not zero here!

If the particle moves from point b to point c in the y direction, what is the change in its potential energy, Uc−Ub?

zero **Every time a charged particle moves along a line of constant potential, its potential energy remains constant and the electric field does no work on the particle.

What is the value of the change in potential energy, ΔU=Uf−Ui, of the alpha particle?

ΔU = −1.10×10−21 J

What was the potential difference that stopped the electron?

ΔV = -1.02 V

A charge q is placed near a group of source charges of total charge Q. Consider q and the group of charges to be a single system. Which of the following quantities does the electric potential energy of the system depend upon? Select all that apply.

q Q q's location relative to the group of charges

At what distance r from a point charge is the electric potential due to that point charge 0 V?

r = ∞