YE OLDE CAPACITOR8.3

InstructorCourse

Today & Beyond

Quiz Material on Capacitors not in the unit. Complete the unit (9)

SPRING BREAK

RETURN Monday – Begin Unit on Magnetism. (Bring to

class) Wednesday – EXAMINATION #2 / Bring in units

4-9 / Lab Reports Due. Friday – Continue magnetism unit.

What is the current through the 4- resistor in this circuit?

a) 0.67 A

b) 0.75 A

c) 1.0 A

d) 1.5 A

e) 4.5 A

Text Answer

DIELECTRIC

Polar Materials (Water)

Apply an Electric Field

Some LOCAL ordering Larger Scale Ordering

Adding things up..

- +Net effect REDUCES the field

Non-Polar Material

APPLICATION OF GAUSS’ LAW

qqq

and

A

qE

E

A

qqE

A

qE

'

'

0

0

0

00

We can measure the C of a capacitor (later)

C0 = Vacuum or air Value

C = With dielectric in place

C=C0

Dielectric Breakdown!

Recall the experiment –

Voltage across C seemed to drop rather than stay stable.

You were given a second capacitor and it held it’s value.

What’s going on??? meters have resistors of 1-10M

14

15

Let’s talk about this…

20.13 RC Circuits

Capacitor charging

RCto eqq 1

RCtime constant

20.13 RC Circuits

Capacitor discharging

RCtoeqq

RCtime constant

Stored Energy

Charge the Capacitor by moving q charge from + to – side.

Work = q Ed=q(V/d)d=qV

W=qV=Sum of strips

0V

0Qq

V

20

00

00

2

1

2

1

CVW

CVQ

VQqVW

20

20

20

2202

2

1

)(2

1

2

1

2

1

2

1

EVol

WityEnergyDens

VolEdAEW

dEd

ACVW

Energy Density

A Thunker

Find the equivalent capacitance between points a and b in the combination of capacitors shown in the figure.

V(ab) same across each

Let’s Finish the Unit