Chapter 3Inductance and Capacitance

CapacitanceCapacitor - a circuit component that has

two parallel metal plates separated by a dielectric

3D Drawing

Circuit Symbols

Capacitance - the measure of the ability of a capacitor to store charge

Voltage Equation for a Capacitor

v=q/C

C = Capacitance in Farads (F)q = Charge on one plate in Coulombs (C)v = Voltage across the capacitor in Volts (V)

Example: What is the charge on a 200F capacitor with 100 Volts across its terminals?

Capacitance Equation

o = permittivity of air, 8.85 x 10-12 F/mr = relative permittivity of the dielectric (Table 3.1)

A = plate area in square meters (m2)d = distance between plates in meters (m)

dAC or

Capacitor ApplicationsKeyboardsSurge SuppressorsRadio TunersCamera Flash Units

Capacitors

Capacitors

Types of CapacitorsElectrolyticOil-filledCeramicVariable Capacitors

How can you vary the capacitance of a capacitor?

Capacitors in SeriesDraw three capacitors in series with a

battery.What is the same for every capacitor in a

series? Answer: Charge

This leads to the Total Capacitance Equation:

321eq C1

C1

C1

C1

Capacitors in ParallelDraw three capacitors in parallel with a

battery. What is the same for every capacitor in

parallel? Answer: Voltage

This leads to the Total Capacitance Equation:

321eq CCCC

CapacitorsCharging CircuitDischarging Circuit

Inductance Inductor - a circuit component that has

two terminals connected to a coil of wire Inductors are also called:

Solenoids Coils Electromagnets

3D DrawingCircuit Symbols

Inductors in SeriesWhat is the same for every inductor in a

series? Answer: Current

This leads to the Total Inductance Equation:

321eq LLLL

Inductors in ParallelWhat is the same for every inductor in

parallel? Answer: Voltage

This leads to the Total Inductance Equation:

321eq L1

L1

L1

L1

Inductance (L) is the measure of an inductors ability to impede current using a magnetic field

It is measured in Henries (H).

dtdiL)t(v

What does the inductance of an inductor depend upon? Answers: Length, Diameter, Core Material,

Number of Turns of Wire

Energy Stored on a Inductor

Inductors also do not dissipate energy like resistors.

They store energy in the form of a magnetic field.

2Li21)t(w

Energy Stored on a Capacitor

Capacitors do not dissipate energy like resistors.

They store energy in the form of charge.

)t(Cv21)t(w 2

DEMO

Examples: (Plots of v and i)What is the voltage across a 10mH

inductor for the following currents?i = 10 Ai(t) = 10A sin(200t)i(t) = 10A cos(200t)

dtdiL)t(v

Exam IThursdayUse the study guide on the course

home pageGraded Homework

Voltage Divider Equation

total321

11 v

RRRRv

Wheatstone Bridge (Balanced Condition)

2

x

1

3g R

RRR for 0i

Example ProblemWhat is the capacitance of a

capacitor with plates with an area of 1 cm2 used to sandwich a polystyrene (r=2) sheet 0.1 mm thick.