Transcript Document

Admin:
• New Assignment posted. Due in a week
• No labs this week
• Test grades and solutions posted. Scripts back today.
• Overall class average is 72%
• Assuming 72% on the tests, 87.3% on the assignments,
and 94.4% on the labs gives a class average of 79.5%
(around C+ / B- )
• I will post the grade scale after the second mid-term.
It will likely be slightly more generous than the SAKAI
default.
Copyright © 2009 Pearson Education, Inc.
Where were we…
Capacitors… I went through 2 examples from
the book – there will be similar problems on the
next test:
Example 24-6: Charge and voltage on capacitors.
Example 24-7: Capacitors reconnected.
series
parallel
Copyright © 2009 Pearson Education, Inc.
Practical Capacitors
Large bodied capacitors
are directly labelled
Copyright © 2009 Pearson Education, Inc.
Practical Capacitors
Small ‘caps’ are usually labelled in pF (‘puffs’) plus a multiplier
Use a third digit of 0 through 5 to place
the corresponding number of 0s
behind the base value.
A third digit of 8 means multiply the
base value by .01. A third digit of 9
means to multiply the base value by
0.1.
For example, 472 would indicate a
4700 pF capacitor and 479 would
indicate a 4.7 pF capacitor.
Copyright © 2009 Pearson Education, Inc.
Two identical
capacitors are
connected as
shown.
What is the final
charge on the
capacitors, if
ε=12V and
C1=C2=10μF?
Copyright © 2009 Pearson Education, Inc.
Inductors: the basics
An inductor is a coil of wire, usually surrounding a conducting core
A current in a coil generates a magnetic field.
A changing magnetic field (i.e. generated by a changing current)
generates a Voltage.
Definition of Inductance (L): vL(t)=-LdI/dt
Constant current produces no voltage
Measured in Henrys (usually milli- micro-)
Energy stored in an inductor: WL= ½ LiL2(t)
(Energy is stored as a magnetic field)
Michael faraday
Inductors
Inductances in series add:
Inductances in parallel combine
like resistors in parallel (almost
never done because of magnetic
coupling)
An inductor in a DC circuit behaves like a short (a wire).
Practical Inductors
Inductors can be labelled with text
Or colour-coded
Copyright © 2009 Pearson Education, Inc.