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Physics 212 and 222Current and Resistance

Current

Batteries

Basic Circuit Elements

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Physics 212 and 222Current and Resistance

•Current is a measure of the movement of charge

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Physics 212 and 222Current and Resistance

Current is defined as the amount of charge that passes through a surface in a given amount of time.

t

QI

The units of current are amps

The direction of the current is opposite to the flow of electrons. It may be thought of as the flow of positive charge.

Current always flows from higher potential to lower potential.

Q

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Physics 212 and 222Current and Resistance

A battery uses chemical reactions to cause a potential difference between the terminals

+ -

The maximum value of the potential difference of a battery is called its voltage

In a circuit diagram we draw it like this

-+

V

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Physics 212 and 222Current and Resistance

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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Physics 212 and 222Current and Resistance

Current is defined as the amount of charge that passes through a surface in a given amount of time

The direction of current is opposite to the flow of electrons

The current may be though of as the flow of positive charge

Current always flows from higher potential to lower potential

In other words, current flows from the positive terminal of the battery through the circuit to the negative terminal

In a circuit diagram we draw it like this

The units of current are amps (A)

-+

V

I

+ -

t

QI

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Physics 212 and 222Current and Resistance

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

BatteryV

- + V

Name Symbol Units

Resistor

Capacitor

Inductor

Switch

RΩ

CF

LH

S

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Physics 212 and 222Current and Resistance

Current

Batteries

Basic Circuit Elements