Physics Test #1 Concepts
In terms of the maximum charge (q0) on a capacitor in an RC circuit, what is the amount of charge on a charging capacitor after two time constants? Assume the capacitor has zero charge when the charging starts.
(0.86)q0
The potential at a distance r from a positive point charge is +V. What is the potential at a distance of r/3?
+3V
An electrically isolated object is electrically neutral. What is the charge on the object if you remove three electrons?
+3e
Suppose a charge -6q is suspended inside a cavity in an electrically neutral cylindrical conductor. What is the charge induced on the interior surface?
+6q
Suppose a charge -6q is suspended inside a cavity in an electrically neutral cylindrical conductor. What is the charge induced on the exterior surface?
-6q
A collection of 11 electrons and 4 protons are contained in a Gaussian (i.e., closed) surface. What is the total electric flux through the surface?
-7 e/E0
A circuit contains a 100-Ω resistor and a 48.0-V battery. An ammeter is inserted into the circuit to measure the current and has an internal resistance of 0.50 Ω. What is the voltage drop across the ammeter terminals?
0.24 V
A single-loop circuit consists of a 9.0 V battery and a 22 Ω resistor. How much current will flow in this circuit?
0.41 A
A circuit is composed of a 12.0 V battery and a 110 Ω resistor. What is the power dissipated by the resistor?
1.3 W
Three resistors of values 22 Ω, 47 Ω, and 68 Ω are connected in series with a 24-V battery. What is the power dissipated by the 47-Ω resistor?
1.4 W
A 12-V car battery has an internal resistance of 0.020 Ω. When the headlights and stereo are on, a current of 25.0 A is drawn from the battery. What is the value of the terminal voltage when this current is drawn from the battery?
11.5 V
Suppose the rms voltage is 110 V in a single-loop circuit that contains a resistor R = 22 Ω. What is the average power dissipated by the resistor in this circuit?
550 W
Suppose that a current of 1.5 A is used to charge a conductor. After 4.0 s, how much charge is delivered to the conductor.
6.0 C
If 2.0 C of charge passes through a wire in time 0.25 s, what is the current in the wire?
8.0 A
The drawing shows a plot of the electric potential V versus the displacement s. The plot consists of four segments. Rank the magnitudeof the electric fields for the four segments, largest to smallest.
D...B...A and C are a tie
Which of the following would increase the capacitance of a parallel-plate capacitor?I. Insert a dielectric between the plates.II. Increase the surface area of each plate.III. Increase the separation distance between the plates.
I and II only
When you bring a negatively charged rod near a piece of electrically neutral plastic it attracts it. What happens if you instead bring a positively charged rod near the plastic?
It attracts.
Suppose an electron is moving with a constant velocity until it encounters a positively charged sphere on its right. How does the sphere alter the trajectory of the electron?
It deflects the electron to the right.
What is the function of the third prong on a power cord to a device?
It provides a safe path to ground in case there is a broken wire inside the device.
Suppose a small, positively charged particle moves past a positively charged sphere with speed . Which one of the following vectors is parallel to the electric field lines of the sphere (at the location of the particle) the instant the particle passes the sphere?
The acceleration of the particle.
A parallel plate capacitor is connected to a battery that maintains a constant potential difference between the plates. If the plates are pulled away from each other, increasing their separation, what happens to the amount of charge on the plates?
The amount of the charge decreases, because the capacitance decreases.
Which one of the following statements concerning the conventional current is true?
The conventional current is the hypothetical movement of positive charges through the wires of an electric circuit.
Suppose the charging control electrode induced a charge on the ink droplets with opposite sign than normal. What change would have to be made to the field between the deflection plates in order to ensure that the ink goes into the gutter?
The field would have to be reversed.
Suppose a thin conducting wire connects two conducting spheres. A negatively charged rod is brought near one of the spheres, the wire between them is cut, and the charged rod is taken away. Which one of the following is true?
The spheres will attract each other.
The 110 V provided by common wall sockets in the United States is given as a root-mean-square (rms) voltage. What is the peak value of the voltage?
V0=155 V
For the circuit shown in the drawing, what is the voltage V1 across resistance R1?
V1=[(R1)/(R1+R2)]V
Kirchhoff's junction rule is a consequence of:
the conservation of charge
Two copper wires have the same length but different cross sectional areas. The cross-sectional area of wire 1 is A, and that of wire 2 is 2A. How are the resistances of the two wires related?
Wire 1 has twice the resistance of Wire 2
Suppose that a current flows through a single-loop circuit containing a battery (voltage V) and a resistor (resistance R). What parameter changes below would reduce the current to half of its original value?
set resistance to 2R
The drawing shows a positive and a negative point charge. The negative charge has the greater magnitude. Where on the line that passes through the charges is the one spot where the total electric field is zero?
to the left of the positive charge
Which one of the following units are the correct SI units for the electromotive force (emf)?
volts (V)
There is an electric field at point P. A very small positive charge is placed at this point and experiences a force. Then the positive charge is replaced by a very small negative charge that has a magnitude different from that of the positive charge. Which one of the following statements is true concerning the forces that these charges experience at P?
They have different magnitudes and different directions.
Two materials have different resistivities. Two wires of the same length are made, one from each of the materials. Is it possible for each wire to have the same resistance?
Yes, if the material with the greater resistivity is used for a thicker wire.
What is the length of time of a typical action potential?
a few milliseconds
Kirchhoff's loop rule is a consequence of:
the conservation of energy
What is magnitude of the acceleration of a particle of mass m and charge +Q placed between the plates of a parallel plate capacitor of charge density o?
a=Qo/E0m
You have five identical resistors. How should they be wired in order to have the minimum possible effective resistance?
all in parallel
Which of the following statements is/are true?I. An equipotential surface is a surface of constant potential.II. The electrostatic force does no work on a charge that moves along an equipotential surface.III. The equipotential surfaces surrounding a point charge consist of an infinite number of concentric spherical shells.IV. Electric field lines are everywhere perpendicular to equipotential surfaces.
all of the above
Suppose a square surface of side 0.10 m is placed in a uniform electric field of magnitude 50.0 N/C. If the angle between the field and the normal to the surface is 25.0o, what is the magnitude of the electric flux through the surface?
0.45 N*m^2/C
Resistors R1=22 Ω and R2=47 Ω are wired in parallel with a battery of voltage V = 12.0 V. R2 is now replaced by a wire. What is the current through R1?
0A
The nucleus of the nitrogen atom has 7 protons. How many electrons does an electrical neutral nitrogen atom have?
7 protons
What is the electrostatic force between and electron and a proton separated by 0.1 mm?
2.3 × 10^-20 N, attractive.
Suppose the human body has a resistance of 500 Ω. How much voltage would be required in order for a life-threating amount of current (0.15 A) to flow through the body?
75 V
Suppose an unknown circuit draws 8.0 A of current when 110 V is applied across its inputs. What is the power dissipated by this circuit?
880 W
Consider the three resistors and the battery in the circuit shown. What is the equivalent resistance in this circuit, if all three resistors have the same resistance R?
3R/2
Suppose the electric field of a point charge of +5q is represented by 20 field lines directed radially outward from the charge. How should the electric field of a point charge of -10q be represented?
40 field lines directed radially inward
When a resistor is wired in a single loop with a battery, the current through the resistor is I. What is the current through the circuit if you wire three more identical resistors in parallel with the first one?
4I
You have three identical resistors that you can connect in various ways. Which of the following is NOT a possible value of the equivalent resistance of the three-resistor combinations?
4R
A voltmeter has an internal resistance of 10 000 Ω and is used to measure the voltage across a 47.0-Ω resistor that, without the voltmeter connected, has a current of 1.20 A pass through it. How much current is drawn away from the circuit by the voltmeter when it is connected across the resistor?
5.6 mA
The drawing shows edge-on views of three parallel plate capacitors with the same separation between the plates. The potential of each plate is indicated above it. Rank the capacitors as to the magnitude of the electric field inside them, largest to smallest.
C, B, A
Consider the following observations: (1) electric field lines are drawn connecting two point charges labeled A and B, (2) charge A is due north of charge B, and (3) a proton placed at the mid-point on a line connecting the two point charges travels due south. Which one of the following statements correctly indicates the signs of the two charges (which have the same magnitude)?
Charge A is positive and charge B is negative.
Suppose a rectangular piece of aluminum has a length D, and its square cross section has the dimensions WxW, where D=2W. What is the ratio of the resistance as measured between the small faces (WxW) to that between the large faces (DxL)?
D^2/W^2
Suppose a negative point charge is placed at x=0 and an electron is placed at some point P on the positive x-axis. What is the direction of the electric field at point P due to the point charge, and what is the direction of the force experienced by the electron due to that field?
E along -x; F along +x
The electric potential V is constant everywhere within a certain region of space. Which statement below is true?
The electric field is zero everywhere within the region.
Charge q1 is placed a distance r0 from charge q2. What happens to the magnitude of the force on q1 due to q2 if the distance between them is reduced to r0/4?
The force increases by a factor of 16.
A rod made from insulating material carries a net charge (which may be positive or negative), whereas a copper sphere is electrically neutral. The rod is held close to the sphere but does not touch it. Which one of the following statements concerning the forces that the rod and sphere exert on each other is true?
The forces are always attractive.
An electrically neutral balloon is rubbed on cloth and becomes positively charged. What can be said about its mass?
The mass decreases.
An electrically neutral object acquires a net electric charge. Which one of the following statements concerning the mass of the object is true?
The mass increases if the charge is negative and decreases if it is positive.
A charge of +2Q and -2Q are located at two of the vertices of an equilateral triangle. Which of the following is true?
The potential at the triangle's empty vertex is zero.
If you place a large number of electrons in one small spot on a conductor, they immediately redistribute themselves on the surface because they repel one another. What happens if you place a large number of electron in one small are on the surface of an insulator?
They stay in the area in which they were initially deposited for a relatively long time because they are not free to move about the insulator.
A positive charge is placed between the plates of a parallel plate capacitor and released from rest at Point B, as shown in the figure. In what direction does the charge move? In the previous question, the work done by the electrostatic force in moving the positive charge from Point B to Point C (Wbc) would be equal to which of the following?
charge moves toward point C The difference in the electrostatic potential energy between Points B and C (EPEb - EPEc).
True or False: There are several common medical diagnostic techniques that utilize the fact that the surface of the human body is an equipotential surface.
false
How does the resistance of a copper wire change when both the length and diameter of the wire are doubled?
it decreases by a factor of two
Suppose the resistor in an RC circuit is doubled in value. How should the value of the capacitance be changed in order to keep the same time constant?
it should be halved
Three points A, B, and C are located along a horizontal line, as the figure shows. A positive charge is released from rest at point A and accelerates toward point B. Upon reaching B, it continues to accelerate toward C. If only motion along the line is allowed, what would a negative charge do if it were released from rest at point B? -------A-------B--------C------
it would accelerate toward A
Suppose the nozzle of the print head in an inkjet printer ejected ink droplets with a higher speed than normal. How would the strength of the field between the deflection plates need to be adjusted to accommodate this higher speed in order to ensure that the ink goes into the gutter?
it would have to increase
A positive charge is moving from point A to point B in a uniform electric field, as shown in the drawing. The electric force does __________ work on the charge and, as a consequence, its electric potential energy __________ .
negative, increases
Since the electric field inside a conducting shell is zero, the shell can be used to shield a volume of space in its interior from external electric fields. Is the opposite effect also true? Can a conducting shell have a charge placed in its interior and shield its exterior from the charge's electric field?
no
In a region of space where the electric field is constant everywhere, as it is inside a parallel plate capacitor, is the potential constant everywhere?
no, the potential is the greatest at the positive plate.
A car battery seems to be malfunctioning (not providing the proper voltage and current to start your car). While the car is off and you are not trying to start it, a friend uses a voltmeter to measure the voltage and finds that your battery voltage is 12.0 V, just as it is supposed to be. After the voltage check, you try to start your car again to no avail. Can you rule out the battery as the problem?
no, there could still be something wrong with the battery
A car has two headlights, and their power is derived from the car's battery. The filament in one burns out, but the other headlight stays on. Are the headlights connected in series or in parallel?
parallel
For two identical capacitors of capacitance C in a circuit containing a battery of voltage V, which configuration of the capacitors stores the most charge?
parallel wiring of the two capacitors
A resistor R is connected to the terminals of a battery with a potential difference V. As a result of the connection, a direct current I passes through the resistor. If the resistor is replaced by a different resistor with a resistance R/3, what effect, if any, will there be on the current passing through the resistor?
the current through the resistor will be 3I
The electric potential is constant throughout a certain region of space. What can you say about the electric field in this region?
the electric field is zero
Consider a spot that is located midway between two identical point charges. Which one of the following statements concerning the electric field and the electric potential at this spot is true?
the electric field is zero, but the electric potential is not zero.
A proton and an electron are held in place on the x axis. The proton is at x = -d, while the electron is at x = +d. They are released simultaneously, and the only force that affects their motions significantly is the electrostatic force of attraction that each applies to the other. Which particle reaches the origin first?
the electron
A proton and an electron are released from rest at the midpoint between the plates of a charged parallel plate capacitor. Except for these particles, nothing else is between the plates. Ignore the attraction between the proton and the electron, and decide which particle strikes a capacitor plate first.
the electron
A proton and electron are simultaneously released from rest at the midpoint between the plates of a charged parallel-plate capacitor. Which particle strikes one of the plates first?
the electron
Two identical resistors (R) are wired in series with a battery of voltage V. Suppose one of the resistors is removed from the circuit. How does the power dissipation of the single resistor compare to the power dissipation of that resistor when the second resistor was in the circuit?
the power dissipation is quadrupled
A capacitor is charged with a battery to a voltage V and then disconnected from the battery. A dielectric is inserted between the plates. When the dielectric is inserted, what happens to the electrostatic potential energy stored in the capacitor?
the stored energy decreases
You have two identical capacitors of capacitance C. Which of the following configurations gives you the smallest equivalent capacitance?
the two capacitors wired in series
The drawing shows three possibilities for the potentials at two points, A and B. In each case, the same positive charge is moved from A to B. In which case, if any, is the most work done on the positive charge by the electric force?
the work is the same in all three cases
Each of three objects carries a charge. As the drawing shows, objects A and B attract each other, and objects C and A also attract each other. Which one of the following statements concerning objects B and C is true?
they repel each other
The electric potential is constant throughout a given region of space. Is the electric field zero or nonzero in this region?
zero
A conducting sphere (shown in grey in the drawing) of radius R has a number q of excess electrons distributed uniformly over its surface. A spherically-shaped Gaussian surface with a radius r < R is represented in the drawing by the dashed circle. Applying Gauss' law, what is the magnitude of the electric field inside the Gaussian sphere?
zero N/C
An ideal ammeter has _________ resistance, whereas an ideal voltmeter has ________ resistance.
zero, infinite