C. Circuits (Chapter 17) Homework Part I
17.1 Batteries and Direct Current
1, 2, 7, 9
17.2 Current and Drift Velocity
11, 12, 13, 14, 19
13: I = q/t solve for t
14: a. I = q/t b. E = DU = qDV
19: a. q = It. Then convert q into number of protons. Remember that each proton has a charge of 1.6 x 10-19C.
b. P = W/t = (# of protons x KE (in eV’s) x 1.6 x 10-19J/ev) / t
17.3 Resistance and Ohm’s Law
20, 21, 22, 23, 25, 32, 37, 40, 42, 46, 48
21: Realize that a perfect ohmic resistor means that it is NOT affected by temp. In the real world, however, there are no perfect ohmic resistors.
25: a. R = rL/A b. A = pd2/4. Therefore, half the diameter means 1/4 the area. So, R increases by 4 times and therefore I will decrease by 1/4.
37: R = Ro (1+aDT). Remember that R = rL/A. You’ll need table 17.1 p. 550.
40: water boils at 100oC
42: R = rL/A solve for L. A = pd2/4
48: first find the initial current (Io) then, use I = V/Ro(1+aDT) to determine second current (I). Subtract I – Io to determine DI.
17.4 Electric Power
49, 50, 51, 52, 53, 56, 58, 60, 65,70
Mr. Young Questions about Traveling and Electricity (Yes, you must answer these too) Don’t peek at the answers until you have tried them!
Young1 = Europe has 240 V coming out of their electric sockets and we have 120 V, who needs more current to run appliances? USA or EU?
Young2 = If you want to plug your 1200 W hair dryer into an outlet in Europe, you know that you need to buy a “converter” before you go “over the pond”. Does this converter effectively increase or decrease the resistance in your hair dryer? (Hint: P = V2/R).
Young3 = Consider the question posed by Young2. What multiple would the resistance change in Europe for your hair dryer? (Hint: USA has 120 V and Europe has 240 V – Europe supplies 2 times the voltage as the US. Hint #2: P = V2/R). If you still need help, let us assume you have resistance (R ) in the USA. What would the effective resistance be in Europe when you hook up your converter: 2R? 4 R? 1/2 R? 1/4 R?…..etc.
50: P = V2/R
51: P = I2R
53: P = V2/R. Higher bulb has smaller resistance so it is thicker.
65: a. E = Pt = Ivt
70: a. I = P/V b. Q = cmDT where c = specific heat of water = 4190 J/kgoC. Water has a mass of 3.785 kg/gal
12: 0.25 A
14: a. 0.30 C b. 0.90 J
22: The one with the smaller slope
32: 75 V
42: 105 m
46: a. yes b. 2.0W
48: a decrease of 0.27 A
52: Power output would quadruple and it would overheat (see young questions)
56: 144 W
58: 1.2 W
60: a. 0.40 A b. 2.4 W
70: a. at least a 30 amp breaker b. 3.1 hours
Young1 = USA draws more current. Remember P = VI. So, if V is low (as it is in the USA, then I must compensate so that the 1200 watt hair dryer can operate)
Young2 = The effective resistance must increase. Realize that V = IR. So, in the US with 120 V, you need a resistance R and you get a current I. But, if V increases, your hair dryer can only take a current I running through its wires. Therefore, you must increase the Resistance when the new 240 volts is applied.
Young3= P = V2/R. So, if V doubles, to 2V, (2V)2 = 4V2. That means that R must increase by a factor of 4. WOW, how cool! I © math, don’t you?