Phy 214 Test 2 5 points each (10 pts free!) Spring 2001
This is a homework assignment Due April 9, 2001 worth 50 points

1. 5.6.2c A single wire across the top of the compass causes a deflection of 30° in needle. If it is now curved back under the compass lined up with the wire on top, the needle will now have:

a. No deflection at all.
b. Only slightly less deflection.
c. Only slightly more deflection.
d. Same deflection in the opposite direction.
e. Twice the deflection in the same direction.

2. RQ5-5. Predict the approximate compass deflection angle in compass 2.

3. RQ5-8 Predict the unknown compass deflection angle in this circuit consisting of three identical light bulbs (these are not the bulbs you used), and explain briefly. Also draw the orientation of the compass needle for both compasses, which lie underneath the wires (looking down on the desktop). Note that a compass deflection is always less than 90 degrees.

4. 5.4.3. Suppose you had one long and one short bulb connected as indicated below, and the long one's filiment has twice the length and same diameter as the short one.

5. Hwk 5-1 You all missed it. Better learn it!

Here is a view from above of a portion of a circuit containing three identical light bulbs (the rest of the circuit including the batteries is not shown).

(a) The compass is placed on top of the wire, and it deflects 20 degrees away from north as shown (the wire is underneath the compass). What direction are the electrons moving at location Pl ? How do you know?

b) In the steady state, 3 x 10⁸ electrons pass location Pl every second. How many electrons pass location P2 every second? Explain briefly.

Do Chapter 6 - 6.7.5 a, b, c. warmups for the problem below.

6. Chapter 6. #1 If two bulbs are hooked in series as indicated below, B1 is the only one that lites . Give a careful explanation for why this could happen.

7. RQ6-5 In the circuit below, all of the wire is made of the same material, but one segment has a much smaller cross sectional area.

Show the steady-state electric field at the locations indicated, including in the thinner segment be sure to use lengths to indicate relative magnitudes.

8. RQ6-7 Most of you missed it. It will probably be on your final.

9. RQ6-9 In a circuit with one battery, conecting wires, and a 12 cm length of nichrome wire, a compass deflection of 6° is observed. What compass deflection would you expect in a circuit containing two batteries in series, connecting wires, and a 36 cm length of nichrome wire that has twice the cross-sectional area as the first?

10. Hwk 6-1

11. Hwk 6-2

12. Assuming all the bulbs are identical,

a. Which is brighter B1 or B4 ?

b. If I1= 8 x 1010 electrons/s,
What is I3=?
What is I5=?

13.

14. RQ7-2: How is the charging time related to the initial current? That is, if the initial current is bigger, is the charging time longer or shorter? Explain briefly.

15. RQ7-5. How does the final charge on the capacitor depend on the kind of bulb or the length of nichrome wire in the circuit during charging? Explain why this is.

16. A certain capacitor made up of two circular disks of cross-sectional area A , and distance s between them is connected to a 10 V battery and receives a total charge Q on the plates. What happens to the charge on the plates when :

a) The cross sectional area A is increased ?

b) The distance between the plates s is doubled?

c) A piece of plastic with dielectric constant 5 is inserted between the plates?
d) Now suppose the capacitor is disconnected from the battery. What is the potential difference between the plates?

17. Hwk 7-1. Here are three circuits labeled A, B, and C. All the long bulbs, capacitors, and batteries are identical, and are like the equipment you used in class. The capacitors are initially uncharged. In each circuit the batteries are connected for a short time T and then disconnected. The time T is only twenty percent of the total charging time through a single long bulb, so that the bulb brightness doesn't change much during the time T.

(a) In which circuit (A, B, or C) does the capacitor now have the most charge? Explain.
(b) In which circuit (A, B, or C) does the capacitor now have the least charge? Explain.

18. Hwk 7-4. Here is a circuit consisting of two flashlight batteries, a large air-gap capacitor, a nichrome wire, and thick copper wires. The circuit is allowed to run long enough that the capacitor is fully charged with +Q and -Q on the plates.

Next you pull the two plates further apart. Describe what happens, and explain why in terms of the fundamental concepts of charge and field (do not use "potential" or "capacitance"). Include diagrams.