Physics 142 Lecture 19

1
Quiz 2 deals with answering questions about
(and calculating values for) charged particle
beams being accelerated and deflected by E and B
fields.
A recap of some in-class problems/questions
dealing with charged particles accelerating
across a potential difference and/or being
steered or deflected by Electric or Magnetic
fields is posted for you at http//csce.unl.edu/
ddaes/Quiz2Review.ppt You might also want to
review the textbooks Assigned problems Ch.19
 P 56, 76 Ch.20 P 17,18 Ch.22 P 17
2
If there is an AC current in a wire loop, there
is a changing B field within the loop. Does
this changing B field induce an EMF (voltage) of
its own in the loop of wire? 1) Yes, it
must 2) No, it does not.
3
AC current produces a changing B field. A
changing B field induces an EMF in a loop, even
the loop that produces the changing B field This
is called self-inductance
1) Yes, it must
4
Self-Induction in Daily Life
When you turn off your toaster by unplugging
it ? current changes rapidly to zero ?
rapidly changing B field produced ? very large
voltage induced in wires of toaster ? spark
5
A solenoid has an inductance of 87.5mH and a
resistance of 0.250?. Find The time constant
for this circuit and how long it takes for
the current to reach ½ its maximum once
connected to a 3volt battery.
? L/R 87.5?10-3H/0.250? 0.350 seconds
6A 12A(1-e-t/t) ½ e-t/t ln(½)
-t/0.350sec t 0.2426 sec
How much energy is stored in this solenoid at
full current?
6
A lamp with a 60W bulb is plugged into a 120v
outlet. a)What are the rms and peak currents
through the lamp? b)What is the bulbs
resistance?
7
A lamp with a 60W bulb is plugged into a 120v
outlet. a)What are the rms and peak currents
through the lamp? b)What is the bulbs
resistance?
but requires a value for R
8
A lamp with a 60W bulb is plugged into a 120v
outlet. a)What are the rms and peak currents
through the lamp? b)What is the bulbs
resistance?
but requires a value for R
Irms60W/120v 0.5 A
9
A lamp with a 60W bulb is plugged into a 120v
outlet. a)What are the rms and peak currents
through the lamp? b)What is the bulbs
resistance?
but requires a value for R
Irms60W/120v 0.5 A
while
so