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Current

Batteries

Basic Circuit Elements

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Current is a measure of the movement of charge

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Zn + 2 OH- —> ZnO + H2O + 2 e-

2 MnO2 + H2O + 2 e- —>Mn2O3 + 2 OH-

Zn + 2MnO2 —> ZnO + Mn2O3 + 1.5 V

Cathode (MnO2) Anode (Zn)

H2OMnO2

MnO2 ZnOH-

OH-

ZnOMn2O3

This is how an alkaline cell (AA battery) works.

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The following circuit elements and their symbolic representation are the ones most commonly found in circuits.

Battery V- + V

Name Symbol Units

Resistor

Capacitor

Inductor

Switch

RΩ

CF

LH

S

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Resistors

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Resistors slow down the electrons

I

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Resistors slow down the electrons

+-

+-

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In most instances, the voltage across a piece of material is proportional to the current that flows through it

This is known as Ohm’s law and is usually written as

The constant of proportionality is called resistance, R, and has units of Ohms (Ω)

IRV

In a circuit diagram we draw resistance like this

R

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Series and Parallel

Resistors in Series

Resistors in Parallel

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A circuit element is in series with another circuit element if at least one side of the element is attached to a side of the another element and nothing else.

A circuit element is in parallel with another circuit element if both sides of the element are attached to separate sides of another element and at least one other thing.

Circuits will often have elements in combination of series and parallel sets.

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R2

-+

V

R1

Resistors in series add together to form an equivalent resistance.

For resistors in series, the currents are the same.

For resistors in series, voltages add.

21 RRReq

21 VVVeq 21 IIIeq

Req

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The inverse of resistors in parallel add together to form the inverse of an equivalent resistance.

For resistors in parallel, the currents add.

For resistors in parallel, voltages are the same.

21 VVVeq 21 IIIeq

R2

-+

V

R1

Req

21

111

RRReq

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Bar Magnets

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N SN S

NN

Bar Magnets get their magnetism from spinning electrons. The spin axis of these electrons align. This is called Ferromagnetism

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N SN S

The direction of the magnetic field vector at any point in space is easily found by using a smaller magnet. This smaller magnet we call a compass.

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N SN S

If we draw the field lines that correspond to these field vectors, they would look like this.

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The magnetic field of the earth is stretched by the solar wind.

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Motion of Charges in Magnetic Fields

Mass Spectrometer

Velocity Selector

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B

R

Force from the magnetic field F q vB

Newton’s Second Law maF2v

mR

2vm q vBR

mv

Rq B

F

v+q

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R2

V-+

Source

Detector

R1

mvR

q B-e-e

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B

E

-ev

q E q vBB

Ev