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Tutorial 01 --
Basic Concept

Fall 2006
ELEC101 BASIC ELECTRONICS


Current

Current I is the rate of flow (change) of charge.
Unit is Ampere (A). 1 A = 1 C / s
Sign Convention of current: the current direction is
defined as the direction that positive (+) charges flow.

Text Box: Instantaneous current
Text Box: Average current





Voltage

Voltage between points A and B is defined as the energy gainedby a 1 C charge moving from B to A.
unit is Volt (V). 1 volt = 1 joule / 1 coulomb.

Text Box: V = dW/dq


Measurement of Voltage

We used multimeter or voltmeter to measure voltage.
The REDterminal is the +veterminal.
The BLACKterminal is the Cveterminal



Voltage

Normally, the voltage we usually use is the Voltage Difference (Potential Difference) between 2 points. So, it is a VECTOR.
We just know the Voltage Difference between A and B is 1.5V. i.e. VAB=1.5V . We do not know VAor VB.



Current and Voltage

A two-terminals element can be characterized by the
1.current entering the terminal, and the
2.voltage across the terminals.



Power in Two Terminal

power = rate of change of energy
Power is measured in watts (W) or Joule/sec (J/s).
1 watt = 1W = (1 volt )( 1 ampere ) = 1VA



Passive Element

P is positive and element absorbs (or dissipates ,
consumes)power from the circuit (v and i have
oppositedirections)



Active Element

P is negative and element supplies (or delivers)
power to the circuit (v and i have samedirections)



Resistance

Ris the resistance.Unit is ohms (symbol )and
1 ohm = 1 volt / 1 ampere = 1=1V/1A


Text Box: . = resistivity of material (.m)(. = 1/. = conductivity), l = length of material (m), A = cross-section area of material for current to flow through (m2).


Resistor

A resistor is a device made to have a specific resistance. Insulators have infinite resistance and superconductors have zero resistance, which implies that electricity can be conducted without loss of energy. A human body is a moderate conductor, enough voltage applied on it can cause serious injury.

Unit is mhos -1 or siemensS



Text Box: Instantaneous power p(t) = v(t) i(t) = i(t)2 R =
Text Box: Average power : P = I2 R =
Text Box: Conductance G = 1/R

Capacitor

Text Box: i(t)
Text Box: q(t) = Cv(t)
Text Box: hence


Text Box: The value of the voltage at any time t, v(t), depends on its initial value v(0) and all the values of the current between time 0 and time t => capacitors have memory
Text Box: A capacitor is a two terminal element whose voltage and charge are linearly related by
Text Box: energy stored in a capacitor


Inductor

An inductor is a two terminal element where the induced flux and current i are related linearly by



Text Box: V-I relation:


Text Box: The value of the current at any time t, i(t), depends on its initial value i(0) and all the values of the voltage between