Phy 132 - Assignment 12:
A.
B. 1
2.
C. 1.
2.
D. 1. It reduces the energy lost to heat. (The rate of heat flow from a resistor = I2R.
So, the less current the better. From P = VI, the way to transmit a lot of power at low
current is at a high voltage.)
2. At resonance, XL cancels XC. (That's what makes it resonate.) So, from
, the answer is: Z = R.
3. From V = IZ, Z = V/I = (50 V)/(4.5 A) = 11.11 Ω
XL = ωL = [2π(400 Hz)](.003 H) = 7.54 Ω
XC = 0 because there is no capacitor.
Z2 = R2 +(XL-XC)2
Z2 - (XL-XC)2 = R2
E. 1. a. - 90° through +90°. (-90° if the circuit is purely capacitive, +90° if purely
inductive. Various mixtures of C, L and R can give you
any
angle in between.)
b. 0° If XL = XC, the opposite side of this triangle has a
length of zero, making the phase angle zero.
2.
F. 1. a. Its charged plates repel additional charge trying to flow in. (Likes repel.) At
higher frequencies, there is less time for charge to accumulate before the current
alternates and it flows out again. Smaller average charge means less repulsion means
less impedance.
b. It’s opposed by the coil’s self-induced emf. A higher frequency changes the current
more rapidly, which induces a larger emf. (E = -L dI/dt.) More opposing emf means
more impedance.
2.