Download Physics 2140, Dr

Physics 2140, Dr. Bellwied’s Class, Practice Handout in SI, SI leader, Kostas, SI times: M: 5:30-6:30 134
State Hall, W: 7:30-9:00 112State Hall, TH: 7:30-9:00 112State Hall, Chapter 20 : Variation of HW
problems from Physics by GIambattista, Richardson, and Richardson (1st edition). (1,2 on handout, HO =
1 from book, BK)(3HO=13 BK)(4,5HO=29BK)(6HO=41BK)(7,8,9HO=49BK)Please print and bring to SI (you
can print 2 pages one side per page).
1. The direction of the inducted current in a loop always opposes the ______ in magnetic ____that
induces the current?
2. In the diagram below three rod loops are moving to the right.
a. What is the current for motional EMF in terms of v, B, L, and R?
b. The current in this conductor moving through a magnetic field develops what values
must be perpendicular to each other?
c. Draw the direction of the magnetic field lines in the diagram below
d. When the rod loop enters from the right, up to the north pole what happens to the
magnetic field?
i. The flux?
1. In turn what happens in terms of induced current and magnetic field?
a. And what direction is the induced current traveling along the
rod
b. Why?
e. When the rod loop exits from the right, leaving the south end what happens to the
magnetic field?
i. The flux?
1. In turn what happens in terms of induced current and magnetic field?
a. And what direction is the induced current traveling along the
rod
b. Why?
f.
What direction is the magnetic force?
g.
What direction is the magnetic force on the rod loop?
3. Everything in this diagram is in the plane of the paper and the loop and wire are held in place by
an external force. For the diagram below the current is decreasing. The loop has a resistance of
33ohms.
a. In what direction does the induced current in the loop flow?
b. What direction does the external force hold the loop in place?
c. At one instant the induced current in the loop is 58mA. What is the rate of change of the
magnetic flux through the loop at that instant in Wb/s?
4. What is a transformer?
a. What happens with the voltage in primary coil is applied in a transformer?
i. In a transformer what is the power equal to in terms of current and emf?
ii. What is the power input equal to in a transformer?
iii. Is there any energy loss in a transformer?
5. A transformer with a primary coil has 2000turns, which is used to step up the standard 170V
amplitude line voltage to 330-V amplitude. How many turns are required in the secondary coil?
6. The current in a 0.070H solenoid decreases from 30.0mA to 180.0mA in 8.0s. Find that average
emf in the solenoid during that time interval.
a. What is self-inductance?
b. Is this an example of self inductance?
c. Give an example of self inductance:
d. What equations are used for self inductance?
e. In a hypothetical example if the current is decreasing what does the induced EMF try to
do with respect to inductance?
7. Current through and inductor must always change ____________, never instantaneously.
8. In an LR circuit, as current builds up, the voltage drop across the resistor _____________then
the induced emf in the inductor gets ___________. The battery emf is ________. When the
current is initially zero, it is because it is charging and the switch is ______. As the switch is
closed for many time constants the current reaches a ________value and the voltage across the
inductor is __________because when the current is no longer changing there is ___ induced
emf.
9. No currents flow in the circuit before the switch is closed. Consider all circuit elements to be
ideal.
a. At the instant the switch is closed, what are the values of the currents I1 and I2 , the
potential differences across the resistors, the power supplied by the battery, and the
induced emf in the inductor?
b. After the switch has been closed for a long time, what are the values of the currents I1
and I2, the potential differences across the resistors, the power supplied by the batter,
and the induced emf in the inductor?