Reminders exam i coming up mon feb 24 th a week from monday
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Reminders: Exam I coming up Mon Feb 24 th ! (a week from Monday). HW3 due on Fri Feb 21. Conduction and Batteries!. Fixed charges. Mobile charges. −. +. −. +. Eventually … . −. Static!. Flow of charges stops!. +. Pixie ↔ electro-chemistry. EMF. Falling water analogy :.

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Reminders: Exam I coming up Mon Feb 24 th ! (a week from Monday)

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Reminders exam i coming up mon feb 24 th a week from monday

Reminders:Exam I coming up MonFeb 24th!(a week from Monday)

HW3 due on Fri Feb 21


Reminders exam i coming up mon feb 24 th a week from monday

Conduction and Batteries!

Fixed charges

Mobile charges


Reminders exam i coming up mon feb 24 th a week from monday

+


Reminders exam i coming up mon feb 24 th a week from monday

+


Reminders exam i coming up mon feb 24 th a week from monday

Eventually …

Static!

Flow of charges stops!

+


Reminders exam i coming up mon feb 24 th a week from monday

Pixie ↔ electro-chemistry


Reminders exam i coming up mon feb 24 th a week from monday

EMF


Reminders exam i coming up mon feb 24 th a week from monday

Falling water analogy:


Reminders exam i coming up mon feb 24 th a week from monday

The perfect battery!

Will provide whatever current is needed.

Always maintains a fixed electric potential

across it’s terminals.


Reminders exam i coming up mon feb 24 th a week from monday

Batteries hooked in series:


Reminders exam i coming up mon feb 24 th a week from monday

Batteries hooked in parallel:


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current!


Reminders exam i coming up mon feb 24 th a week from monday

Current (conventional)!


Reminders exam i coming up mon feb 24 th a week from monday

We’ll always assume conventional current flow:

A current of positive charge moving from + to −.

The real current (electrons) going backward is

completely equivalent (for our purposes!)

Units?


Reminders exam i coming up mon feb 24 th a week from monday

Example 18-1: A current of 1.30 A flows in a wire. How many electrons are flowing past any point in the wire per second?


Reminders exam i coming up mon feb 24 th a week from monday

Ohm’s Law


Reminders exam i coming up mon feb 24 th a week from monday

Ohm’s Law

Resistance: depends on the object’s size, shape, and composition.

Units?


Reminders exam i coming up mon feb 24 th a week from monday

Standard symbol


Reminders exam i coming up mon feb 24 th a week from monday

Example: 18.7 An electric clothes dryer has a heating element with a resistance of 9.6 . (a) What’s the current in the element when connected to 240 V? (b) How much charge passes through the element in 50 min?


Reminders exam i coming up mon feb 24 th a week from monday

The water analogy again!

Large ‘resistance’

small ‘resistance’

2 Gal/min

10 Gal/min


Reminders exam i coming up mon feb 24 th a week from monday

Perfect wires!

A perfect wire has zero resistance (negligible resistance compared to other stuff)

So, no potential drop along wire

That is …. (for example)


Reminders exam i coming up mon feb 24 th a week from monday

Perfect wires!

A perfect wire has zero resistance (negligible resistance to other stuff)

So, no potential drop along wire

Whatever V is here …


Reminders exam i coming up mon feb 24 th a week from monday

Perfect wires!

A perfect wire has zero resistance (negligible resistance to other stuff)

So, no potential drop along wire

Whatever V is here …

It’s the same here!

No matter what current is flowing!


Reminders exam i coming up mon feb 24 th a week from monday

Points at the same electric potential….


Reminders exam i coming up mon feb 24 th a week from monday

Points at the same electric potential….

Every point of the same color is at the same potential!


Reminders exam i coming up mon feb 24 th a week from monday

Large ‘resistance’

Small ‘resistance’


Reminders exam i coming up mon feb 24 th a week from monday

Resistivity of a material

Resistance: depends on the object’s size, shape, and composition.

Resistivity: depends ONLY on the object’s composition.


Reminders exam i coming up mon feb 24 th a week from monday

Example: 18.13 What is the resistance of a 3.5 m length of copper wire 1.5 mm in diameter?


Reminders exam i coming up mon feb 24 th a week from monday

Example: Now, how much current will flow in that wire if it’s hooked up to a 1.5 V battery?


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