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Unformatted text preview: PHYS 153 Term 2, 2008-09 Homework 6A
Mar. 2 - 6 Problem 1
How much current ﬂows through the bottom wire in the ﬁgure below, and in which direction? 6Ω 10 Ω 9V 12 Ω 24 Ω + _
+ _ + _
15 V Bottom Wire Figure 1: ﬁg. for Problem 1 The switch in the ﬁgure has been closed for a very long time. (a) What is the charge on the capacitor? (b) The switch is opened at t = 0 s. At what time has the charge on the capacitor decreased to 10% of its initial value?
Opens at t = 0 s 60 Ω 10 Ω 100 V 40 Ω 2.0 µF Figure 2: ﬁg. for Problem 2 Problem 3
The Wheatstone Bridge The circuit shown in the ﬁgure below, called a Wheatstone bridge, is used to determine the value of an unknown resistor X by comparison with three 1-1 resistors M , N , and P whose resistances can be varied. For each setting, the resistance of each resistor is precisely known. With switches K1 and K2 closed, these resistors are varied until the current in the galvanometer G is zero; the bridge is then said to be balanced. (a) Show that under this condition the unknown resistance is given by X = M P/N . (This method permits very high precision in comparing resistors.) (b) If the galvanometer G shows zero deﬂection when M = 850.0 Ω, N = 15.00 Ω, and P = 33.48 Ω, what is the unknown resistance X ? G
Figure 3: ﬁg. for Problem 3 Problem 4
An electron in a cathode-ray tube is accelerated through a potential diﬀerence of 10 kV, then passes through the 2.0-cm-wide region of uniform magnetic ﬁeld in the ﬁgure below. What ﬁeld strength will deﬂect the electron by 10◦ ? Figure 4: ﬁg. for Problem 4 Problem 5
A proton moving in a uniform magnetic ﬁeld with v1 = 1.00 × 106ˆ m/s experiences force i ˆ ˆ F1 = 1.20 × 10−16 k N. A second proton with v2 = 2.00 × 106 ˆ m/s experiences F2 = j ˆ −4.16 × 10−16 k N in the same ﬁeld. What is B ? Give your answer as a magnitude and an angle measured ccw from the +x-axis. 1-2 ...
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