Moving Charges Worksheet

Scribe for Tuesday, December 16, 2008 since Eric was kidnapped by Santa Claus and his evil green elves and hasn't scribed since.


AGENDA:

* Corrected Moving Charges Worksheet #1-10
* Read Magnetic Formulae handout
* Chapter 27 Review #1-7 for homework

The Moving Charges Worksheet was difficult to do at first, which is why Ms.K suggested on doing the questions in reverse order. Then it’s just a matter of knowing how to use your formulas correctly. Also, visualizing the problem (i.e. drawing a picture) helps a lot too.


MOVING CHARGES WORKSHEET

10. An electron is moving east to west at 5.0 x 10^5 m/s through a magnetic field. A force of 4.0 x 10-6 N north is acting on the electron. What is the magnitude and direction of the magnetic field?

F = Bqv
(4.0 x 10^6) = B (1.6 x 10^-19) (5.0 x 10^8)
B = 5 x 10^7 (into page)


9. What is the magnitude and direction of a magnetic force on a proton moving horizontally to the north at 8.6 x 10^4 m/s, as it enters a magnetic field of 1.2 T pointing vertically upward?

F = Bqv = (1.2 N/(c*m/s)) (1.6 x 10^19 C) (8.6 x 10^4 m/s) = 1.7 x 10^014 [right]


8. An electron experiences the greatest force by a magnetic field as it travels at 2.1 x 10^5 m/s when it is moving south. The force is 5.6 x 10^-13 N and up. Find the magnitude and direction of the magnetic field.

F = Bqv
(5.6 x 10^-13)/ [(1.6 x 10^-29) (2.1 x 10^5)] = B
B = 16.7 T [left]


7. A 10.0 m long high tension power line carries a current of 20.0 A perpendicular to the earth’s magnetic field of 5.5 x 10^-5 T. What is the magnetic force experienced by the power line?

F = BIL = (5.5 x 10^-5 T) (20.0 A) (10.0 m) = 0.011 N


6. A wire connecting a taillight to a motorcycle battery is 0.50 m long and is perpendicular to the Earth’s magnetic field. It experiences a force of 6.0 x 10^-5 N when carrying a current of 1.5 A. What is the magnitude of the Earth’s magnetic field at that location?

F = BIL
6.0 x 10^-5 N = B (1.5 A) (0.50 m)
B = 8 x 10^-5 T


5. A 15 cm length of wire carries a current of 20.0 A. It is perpendicular to a uniform magnetic field. If it experiences a magnetic force of 0.40 N, what is the magnetic field intensity?

B = F/(IL) = 0.4 N / (20.0 A x 0.15 m) = 0.13 T


4. Using the Millikan apparatus, a sphere of mass 3.2 x 10^-15 kg is held motionless. The plates produce an electric field strength of 19 600 N/C.


a) What forces are acting on the sphere?
electric force, gravitational force

b) What type of charge must be on the sphere?
positive

c) Determine the amount of charge on the sphere.
F_g = F_e
mg = Eq
q = mg/E = (3.2 x 10^-15 kg) (9.8 N/kg) / (19 600 N/C) = 1.6 x 10^-18 C

d) How many electrons does this correspond to?
(1.6 x 10^-18 C) x (1 electron)/(1.6 x 10^-19 C) = 10 electrons


3. The electric field between these charged parallel plates is 23 800 N/C. The drop’s mass is 2.4 x 10^-14 kg. What force would be experienced by the drop if it had the charge of three excess electrons?


F_e = Eq = (23 800 N/C) (3 x 1.6 x 10^-19 C) = 1.14 x 10^-14 N [up]
F_g = mg = (2.4 x 10^-14 kg) (9.8 N/kg) = 2.35 x 10^-13 N [down]
F_net = 2.35 x 10^-13 N - 1.14 x 10^-14 N = 2.24 x 10^-13 [down]


2. The plates are 5.0 cm apart and produce an electric field strength of 1200 N/C in the region between them. An electron enters the electric field at 1.00 x 10^2 m/s. With what velocity does the electron strike the positive plate? (Ignore gravity.)


F_e = qE = (-1.6 x 10^-19 C) (1200 N/C) = 1.92 x 10^-15 N
ma = qE
a = qE/m = (1.92 x 10^-15 N) / (9.11 x 10^-3 kg) = 2.11 x 10^14 m/s^2
v_f^2 = v_i^2 + 2ad
v_f = [(1.00 x 10^2 m/s)^2 + 2 (2.11 x 10^14 m/s^2) (0.05 m)]^0.5 = 4.6 x 10^6 m/s


1. This oil drop of mass 4.5 x 10^-15 kg has had two electrons removed. The electric field strength is 3.0 x 10^4 N/C.


a) What will happen to the drop?
F_g = mg = (4.5 x 10^-15 kg) (9.8 N/kg) = 4.4 x 10^-14 N
F_e = Eq = (3.0 x 10^4 N/C) (2 x 1.6 x 10^-19 C) = 9.5 x 10^-15 N
F_g > F_e, so drop will fall

b) What is the total force experienced by the drop?
F_net = 4.4 x 10^-14 N + 9.5 x 10^-15 N = 3.45 x 10^-14 N [down]

Next scribe is DANA.

Charges, Energy, Voltage Lab

Answers to 33-2 Electrical Fields and Potential are found on slides 1 and 2.
Answers to Electric Potential are found on slides 3 to 7.

After reviewing our answers to those worksheets, we did a lab entitled Charges, Energy, Voltage from Chapter 21 of the green book.

In the lab, we developed a model that showed the different amounts of charges at different energy levels. We erected a ruler in a Playdoh substance and made markings at 3 cm, 6 cm, 9 cm, and 12 cm. The 3 cm resembled 3 V or 3 J/C, the 6 cm resembled 6 V or 6 J/C, etc. We taped 4 pennies at the 3 cm marking, 3 pennies at the 6 cm marking, 2 pennies at the 9 cm marking, and a penny at the 12 cm marking. Each penny resembled a Coulomb.

A lab worksheet was handed out and has to be completed.

Next scribe is Vieteran.

Kepler's Three Laws Videotape

No one was selected for scribe in physics, so I'm assuming today's scribe post is up for grabs.

I am zeph. zeph is scribe. Today's scribe post has been zephed!

Answers to "8.1 Motion in the Heavens and on Earth: Kepler's Laws of Planetary Motion" and "Kepler's Three Laws Videotape" are given below.

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8.1 MOTION IN THE HEAVENS AND ON EARTH

Kepler's Laws of Planetary Motion

Tycho Brahe studied the motion of the planets in order to be able to PREDICT astronomical events. He believed that EARTH was the centre of the universe. Johannes Kepler believed that THE SUN was the centre of the universe. He analyzed Brahe's data, and developed THREE laws of planetary motion. One law says that the paths of the planets are ELLIPSES with THE SUN located at one focus. Another law states that an imaginary line extending from the sun to a planet will sweep out equal AREAS in equal amounts of time. According to this law, planets move FASTEST when closest to the sun and move SLOWEST when farthest from the sun. Kepler's last law states that the ratio of the squares of the PERIODS of any two planets in orbit around the sun is equal to the ratio of the CUBES of their distances from THE SUN. This law can be states as an equation, (T_A/T_B)^2 = (R_A/R_B)^2. To use this law to calculate the period of a satellite, you must know the RADIUS of its orbit and the PERIOD and RADIUS of the orbit of another satellite.

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KEPLER'S THREE LAWS VIDEOTAPE

Answer the following questions based on the videotape entitled "Kepler's Three Laws".

1. What planetary model did Johannes Kepler believe in?
Copernican

2. What planet's orbit did Kepler analyze?
Mars

3. How far off from a circle was the oribt of Mars?
8 min arc or 1/4th of the apparent width of the moon

4. What type of curve can explain the orbit of Mars?
ellipse

5. In an ellipse, is the total distance from 1 pin to the string and then to the other pin a constant?
yes

6. The name given to a single point in an ellipse is the __________.
focus point

7. Focus is the Latin word for __________.
fireplace

8. How would you describe Kepler's childhood?
poverty and illness

9. What journey did Kepler undertake in 1600 and for what purpose?
went to see Tycho Brahe in Denmark to learn more astronomy

10. What was a main interest of Tycho Brahe?
astronomy

11. How did Kepler obtain the careful observations that Brahe made during his lifetime?
stole it

12. Was the Copernican model of the universe easy to justify scientifically?
no

13. What were some of the problems that faced Kepler in discovering the secrets of the sky?
planets are in motion in its orbit and rotates on axis

14. How many pages of calculations did Kepler have?
about 900 pages

15. What does "in opposition" mean according to the positions of Mars, Earth, and sun?
Mars is in the same position as the Earth and the sun

16. Can any circle viewed obliquely be termed an ellispe?
yes

17. In ancient history, which group of people studied conic sections?
Greeks

18. Is a parabola a popular shape in our world today?
yes

19. In your own words, describe he term eccentricity?
how flat an ellipse is

20. State Kepler's 3 laws.
a) 1st: Each planet moves in an ellipse with the sun as its focus.
b) 2nd: A line from the sun to each planet sweeps out equal areas in equal times.
c) 3rd: T^2 directly proportional to R^3

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HOUSEKEEPING
Homework:
* 8.1 Motion in the Heavens and on Earth Study Guide
* Exploration of Space Project due Thursday, November 27.
Next scribe is ERICT.