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Phy 213: Chap 25-26

Terms in this set (76)

U1/U2 = 6
Charge q1 is distance r from a positive point charge Q. Charge q2=q1/3 is distance 2r from Q. What is the ratio U1/U2 of their potential energies due to their interactions with Q?
U1/U2 = 1.5
Charge q1 is distance s from the negative plate of a parallel-plate capacitor. Charge q2=q1/3 is distance 2s from the negative plate. What is the ratio U1/U2 of their potential energies?
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Look at the following picture! You will use for next two slides.
The electric potential energy increases.
Does the electric potential energy increase, decrease, or stay the same?
The electron's speed at f is less, than it's speed at i.
Is the electron's speed at f greater than, less than, or equal to its speed at i?
What will be the final speed of an electron released from rest at the negative plate?

v =
2.4×10^6 ms
A proton is released from rest at the positive plate of a parallel-plate capacitor. It crosses the capacitor and reaches the negative plate with a speed of 55000 m/s .
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Look at the following picture. You will use it for the next slide.
U = −8.6×10−6 J
What is the electric potential energy of the group of charges in (Figure 1) ? Assume that q = -6.5 nC.
ΔV = 5200 V
What potential difference is needed to accelerate a He+ ion (charge +e, mass 4 u) from rest to a speed of 5.0×105 m/s ?
ΔVC = 970 V
Two 2.20-cm-diameter disks spaced 2.10 mm apart form a parallel-plate capacitor. The electric field between the disks is 4.60×105 V/m .

What is the voltage across the capacitor?
v = 1.7×107 ms
An electron is launched from the negative plate. It strikes the positive plate at a speed of 2.50×107 m/s . What was the electron's speed as it left the negative plate?
-6580 V
A 0.700 mm -diameter ball bearing has 1.60×109 excess electrons.
What is the ball bearing's potential?
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Look at the slide. You will use it for the next slide.
q =
10 nC
The electric potential at the dot in the figure is 3140 V

What is charge q?
x0 = 2.76,3.29 cm
A 11.5 nC charge is at x = 0cm and a -1.0 nC charge is at x = 3 cm .

At what point or points on the x-axis is the electric potential zero?
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Look at the next slide. You will use it for the next slide.
It's speed is 1.01*10^5 m/s.
A proton's speed as it passes point A is 5.00×104 m/s . It follows the trajectory shown in the figure. What is the proton's speed at point B?
v = 7.5×107 ms
What is the escape speed of an electron launched from the surface of a 1.0-cm-diameter glass sphere that has been charged to 9.0 nC ? Assume vo=o m/s

Express your answer to two significant figures and include the appropriate units.
...
Look at the slide. You will need it for the next slide. This shows an electric field diagram. Dashed lines 1 and 2 are two surfaces in space, not physical objects.
higher
Is the electric potential at point a higher that, lower that, or equal to the electric potential at point b?
ΔVef ΔVcd ΔVab
Rank in order, from largest to smallest, the magnitudes of the potential differences ΔVab, ΔVcd, and ΔVef.
Yes. The E field is perpendicular to the surface.
Is surface 1 an equipotential surface? Why ?
No. The E field is not perpendicular to the surface.
Is surface 2 an equipotential surface? Why?
Vf−Vi = -600 V
What is the potential difference between xi=20cm and xf=40cm in the uniform electric field Ex=3000V/m?
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You will need the following slide for the next slide.
ΔV = 50 V
What is the potential difference between xi = 2.0 m and xf = 3.0 m ?

Express your answer to two significant figures and include the appropriate units.
...
The dashed lines in the diagram represent cross sections of equipotential surfaces drawn in 1 V increments. (Figure 1)
0 J
What is the work done by the electric force to move a 1 C charge from A to B?
1 J
What is the work done by the electric force to move a 1 C charge from A to D?
greater than the magnitude of the electric field at point B.
The magnitude of the electric field at point C is

-greater than the magnitude of the electric field at point B.
-less than the magnitude of the electric field at point B.
-equal to the magnitude of the electric field at point B.
-unknown because the value of the electric potential at point C is unknown.
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Look at the following slide. You will need it for the next slides.
down
What is the direction of the electric field at the dot in the figure (Figure 1) ?
E = 20 kV/m
What is the magnitude of the electric field at the dot?
-885 V/m
The electric potential in a region of uniform electric field is -300 V at x = -1.50 m and + 2000 V at x =+ 1.10 m .
What is Ex?
Express your answer with the appropriate units.
...
The two metal spheres in the figure(Figure 1) are connected by a metal wire with a switch in the middle. Initially the switch is open. Sphere 1, with the larger radius, is given a positive charge. Sphere 2, with the smaller radius, is neutral. Then the switch is closed. Afterward, sphere 1 has charge Q1, is at potential V1, and the electric field strength at its surface is E1. The values for sphere 2 are Q2, V2, and E2.
V1=V2
Is V1 larger than, smaller than, or equal to V2?
Q1>Q2
Is Q1 larger than, smaller than, or equal to Q2?
E1<E2
Is E1 larger than, smaller than, or equal to E2?
6.00 μJ
How much work does the charge escalator do to move 2.00 μC of charge from the negative terminal to the positive terminal of a 3.00 V battery?

Express your answer with the appropriate units.
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You will use the following prompt for the next slides:

Two 2.0-cm-diameter aluminum electrodes are spaced 0.50 mm apart. The electrodes are connected to a 150 V battery.
C = 5.6 pF
What is the capacitance?
Express your answer with the appropriate units.
Q = 0.83 nC
What is the magnitude of the charge on each electrode?

Express your answer with the appropriate units.
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You will use the following slide for the next slide:
Ceq = 7.5μF
What is the equivalent capacitance of the three capacitors in the figure (Figure 1) ?
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You will use the following prompt for the next slides:

The electric potential in a region of space is V=( 110 x^2− 290 y^2)V, where x and y are in meters.
E = 1800 V/m
What is the strength of the electric field at (x,y)=(1.0m,3.0m) ?

Express your answer using two significant figures.
θ = 97.2 ∘ counterclockwise from the positive x-axis
What is the direction of the electric field at (x,y)=(1.0m,3.0m) ? Give the direction as an angle (in degrees) counterclockwise from the positive x-axis.
...
In the figure are shown three capacitors with capacitances C1=6.00μF, C2=3.00μF, C3=5.00μF. The capacitor network is connected to an applied potential Vab. After the charges on the capacitors have reached their final values, the charge Q2 on the second capacitor is 40.0 μC
Q1 = 80.0μC
What is the charge Q1 on capacitor C1?
Q3 = 120μC
What is the charge on capacitor C3?

Express your answer in microcoulombs to three significant figures.
Vab = 37.3 V
What is the applied voltage, Vab?

Express your answer in volts to three significant figures.
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You will use the following slide for the next slides.
Q1, Q2, Q3 = (60,29,29)μC
What is the charge on each capacitor in the figure, if ΔV = 12 V ?(Figure 1)

Enter your answers numerically separated by commas.
ΔV1, ΔV2, ΔV3 = (12,7.2,4.8)V
What is the potential difference across each capacitor in the figure?

Enter your answers numerically separated by commas.
U = (0.5)((Q)^2/C)
Find the energy U of the capacitor in terms of C and Q by using the definition of capacitance and the formula for the energy in a capacitor.

Express your answer in terms of C and Q.
U = 0.5(C)(V)^2
Find the energy U of the capacitor in terms of C and V by using the definition of capacitance and the formula for the energy in a capacitor.

Express your answer in terms of C and V.
U/U0 = 0.5: The voltage across the capacitor is constant.
A parallel-plate capacitor is connected to a battery. The energy of the capacitor is U0. The capacitor remains connected to the battery while the plates are slowly pulled apart until the plate separation doubles. The new energy of the capacitor is U.

Find the ratio U/U0. https://phet.colorado.edu/en/simulation/legacy/capacitor-lab
U/U0 = 2: The charge across the capacitor is constant.
A parallel-plate capacitor is connected to a battery. The energy of the capacitor is U0. The capacitor is then disconnected from the battery and the plates are slowly pulled apart until the plate separation doubles. The new energy of the capacitor is U.
Find the ratio U/U0.
U = (0.5)(ϵ0A/d)(V)^2
A parallel-plate capacitor has area A and plate separation d, and it is charged to voltage V. Use the formulas from the problem introduction to obtain the formula for the energy U of the capacitor.

Express your answer in terms of A, d, V, and appropriate constants.
5.6 μF
The flash unit in a camera uses a 6.0 V battery to charge a capacitor. The capacitor is then discharged through a flashlamp. The discharge takes 10μs, and the average power dissipated in the flashlamp is 10 W.

What is the capacitance of the capacitor?
Express your answer with the appropriate units.
2.00 × 10^20 electrons flow through a cross section of a 3.60-mm-diameter iron wire in 5.00 s .

What is the electron drift speed?
46.2 μm/s
Which, if any, of these statements are true? (More than one may be true.) Assume the batteries are ideal.

A battery is a source of potential difference; the potential difference between the terminals of the battery is always the same.

A battery is a source of current; the current leaving the battery is always the same.

A battery supplies the energy to a circuit.
A battery is a source of potential difference; the potential difference between the terminals of the battery is always the same.

A battery supplies the energy to a circuit.
A metallic wire has a diameter of 4.12mm. When the current in the wire is 8.00A, the drift velocity is 5.40×10−5m/s.


What is the density of free electrons in the metal?
6.9×10^28 m−3
A 6.6×10−4 V/m electric field creates a 4.1×1017 electrons/s current in a 1.9-mm-diameter aluminum wire.

What is the drift speed?
vd = 2.4×10−6 m/s
A 6.6×10−4 V/m electric field creates a 4.1×1017 electrons/s current in a 1.9-mm-diameter aluminum wire.

What is the mean time between collisions for electrons in this wire?
τ =
2.1×10−14 s
In an integrated circuit, the current density in a 2.0-μm-thick × 70-μm-wide gold film is 7.5×105 A/m2 .

How much charge flows through the film in 15 min?
Q = 9.5×10−2 C
A hollow copper wire with an inner diameter of 1.2 mm and an outer diameter of 1.8 mm carries a current of 12 A .

What is the current density in the wire?
J = 8.5×10^6 Am2
A 20-cm-long nichrome wire is connected across the terminals of a 1.5 V battery.

What is the electric field inside the wire?

Express your answer to two significant figures and include the appropriate units.
E = 7.5 Vm
A 20-cm-long nichrome wire is connected across the terminals of a 1.5 V battery.

What is the current density inside the wire?

Express your answer to two significant figures and include the appropriate units.
J =
5.0×10^6 Am2
A 20-cm-long nichrome wire is connected across the terminals of a 1.5 V battery.

If the current in the wire is 2.4 A , what is the wire's diameter?
Express your answer to two significant figures and include the appropriate units.
d =
0.78 mm
What is the resistance of

A 1.50 m long copper wire that is 0.800 mm in diameter?
5.07×10−2 Ω
What is the resistance of

A 20.0 cm long piece of carbon with a 0.500 mm × 0.500 mm square cross section?
28.0 Ω
The terminals of a 0.70 Vwatch battery are connected by a 90.0-m-long gold wire with a diameter of 0.200 mm .

What is the current in the wire?

Express your answer using three significant figures.
I = 10.2 mA
A sculptor has asked you to help electroplate gold onto a brass statue. You know that the charge carriers in the ionic solution are singly ionized gold ions, and you've calculated that you must deposit 0.50 g of gold to reach the necessary thickness.

How much current do you need, in mA, to plate the statue in 1.5 hours?
I = 45 mA
The starter motor of a car engine draws a current of 200 A from the battery. The copper wire to the motor is 4.00 mm in diameter and 1.2 m long. The starter motor runs for 0.830 s until the car engine starts.

How much charge passes through the starter motor?
166 C
The starter motor of a car engine draws a current of 200 A from the battery. The copper wire to the motor is 4.00 mm in diameter and 1.2 m long. The starter motor runs for 0.830 s until the car engine starts.

How far does an electron travel along the wire while the starter motor is on?
0.971 mm
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