Version 001 – HW18 – gavrin – (25111) 1 This print ... - Web Physics

Version 001 – HW18 – gavrin – (25111) 1
This print-out should have 12 questions.
Multiple-choice questions may continue on
the next column or page – find all choices
before answering.
Long and Skinny
001 (part 1 of 2) 10.0 points
Assumethatthelengthofthesolenoidismuch
larger than the solenoid’s radius and that the
core of the solenoid is air.
Calculate the inductance of a uniformly
wound solenoid having 230 turns if the length
ofthesolenoid is37 cm and itscross-sectional
area is 4 cm 2 .
Correct answer:
mH.
002 (part 2 of 2) 10.0 points
Calculate the self-induced emf in the solenoid
described in the first part if the current
through it is decreasing at the rate of 49 A/s.
Correct answer:
mV.
Inductance of a Solenoid
003 (part 1 of 2) 10.0 points
A solenoid has 104 turns of wire uniformly
wrapped around an air-filled core, which has
a diameter of 11 mm and a length of 4.2 cm.
The permeability of free space is
1.25664×10 −6 N/A 2 .
Calculate the self-inductance of the
solenoid.
Correct answer: 3.07541×10 −5 H.
004 (part 2 of 2) 10.0 points
The core is replaced with a soft iron rod that
has the same dimensions, but a magnetic permeability
of 800µ 0 .
What is the new inductance?
Correct answer: 0.0246033 H.
Inductor in a Circuit 02
005 10.0 points
An inductor that has a resistance of 10 kΩ is
connected to an ideal battery of 128 V. 3 ms
seconds after the switch is thrown the current
in the circuit is 9.472 mA.
Calculate the inductance.
Correct answer: 22.2705 H.
Simple LR Circuit
006 10.0 points
At times prior to t = 0, the switch is open.
The switch is closed at t = 0.
4 kΩ
S
I
12 mH
240 V
When I = 11 mA, what is the potential
difference across the inductor?
Correct answer: 196 V.
Increase and Decay of Current 01
007 (part 1 of 3) 10.0 points
An inductor and a resistor are connected
with a double pole switch to a battery as
shown in the figure.
The switch has been in position b for a long
period of time.
7.65 Ω
9.5 V
137 mH
S b
If the switch is thrown from position b
to position a (connecting the battery), how
much time elapses before the current reaches
95 mA?
Correct answer: 1.42524 ms.
008 (part 2 of 3) 10.0 points
Whatisthemaximumcurrent intheinductor
a long time after the switch is in position a?
a

Version 001 – HW18 – gavrin – (25111) 2
Correct answer: 1.24183 A.
009 (part 3 of 3) 10.0 points
The switch has brushes within it so that the
switch can be thrown from a to b without
internalsparking. Nowtheswitchissmoothly
thrown from a to b, shorting the inductor and
resistor.
How much time elapses before the current
falls to 141 mA?
Correct answer: 38.9614 ms.
Energy Stored in an Inductor
010 10.0 points
In an RL series circuit, an inductor of 3.03 H
andaresistorof8Ωareconnected toa28.4V
battery. The switch of the circuit is initially
open. Next close the switch and wait for a
long time. Eventually the current reaches its
equilibrium value.
At this time, what is the corresponding
energy stored in the inductor?
Correct answer: 19.0928 J.
Time Constant and Current
011 (part 1 of 2) 10.0 points
The switch in the figure is closed at t = 0.
ε
L
R
Find the time constant of the circuit if L =
35.2 mH, E = 9.83 V, R = 4.78 Ω.
Correct answer: 7.36402 ms.
012 (part 2 of 2) 10.0 points
Calculate the current in the circuit at t =
2.13 ms.
Correct answer: 0.516529 A.
S