Circuit Analysis I

Recap Active and Passive electronic components Current: Flow of charges Voltage: Work done per unit charge Ampere and Volt Unit Prefixes: milli, micro, Mega, Kilo etc Scientific notation: 3.1 x 106

Today’s Menu Resistance Types of resistors Voltage sources Current sources Basic electrical circuit Ohm’s Law Simple calculations using Ohm’s Law

Resistance Resistance is the opposition to current i.e. hindrance in the path of current One ohm (1 Ω) is the resistance if one ampere (1 A) current flows in a material when one volt (1 V) is applied across it. Conductance is the reciprocal of resistance: SI Unit of coComponents designed to have a specific amount of resistance are called resistors. nductance is Siemens (mho). Symbols for resistors

Types of Resistors There are four main types of resistors on the basis of material and construction: Carbon Composition Resistor - Made of carbon dust or graphite paste, low wattage values   Film or Cermet Resistor - Made from conductive metal oxide paste, very low wattage values Wire-wound Resistor - Metallic bodies for heatsink mounting, very high wattage ratings and high precision Semiconductor Resistor - High frequency/precision surface mount thin film technology

Types of Resistors On the basis of resistance value there are two types: Fixed resistors and variable resistors Variable resistors include the potentiometer and rheostat. A potentiometer can be connected as a rheostat. The center terminal is connected to the wiper

Resistor color coding

Test yourself What is the resistance and tolerance of each of the four-band resistors? 5.1 kW ± 5% 820 kW ± 5% 47 W ± 10% 1.0 W ± 5%

Electromotive force Voltage generated by a battery is termed as its electromotive force (measured in volts not Newtons) A source of emf can be thought of as a kind of charge pump that acts to move positive charge from a point of low potential through its interior to a point of high potential by chemical, mechanical or other means. In circuit theory two types of sources exist: 1. Current Sources 2. Voltage Sources

Ideal Voltage Source Voltage across it is independent of the current through it. Ideal voltage source has no internal resistance Real voltage sources do have a finite internal resistance

Ideal Current Source Current does not depend upon any voltage(s).

Electric Circuit An interconnection of electronic components designed to produce a desired result. A basic circuit consists of a source, a load, and an interconnecting path.

Ohm’s Law Current established is directly proportional to the voltage applied in a circuit. Formula for voltage, V=IR V=voltage I=current R=resistance

Formula for current: I=V/R Formula for resistance: R=V/I

Calculate current when resistance and voltage are known: Example: V=100 V, R=22 Ω, I=? I = V / R = 100 / 22 = 4.55 A There are 4.55 A in this ciruit.

If the resistance is changed to 47 ohm and voltage to 50V, what is the new value of current? I = V / R = 50 / 47 = 1.06 A

When voltage is 50V and resistance is 1.0kΩ, find the value of current? Remember 1.0kΩ is equal to 1 x 103 Ω , so current will be I = 50 V / 1.0 kΩ = 50 V / 1 x 103 Ω = 50 x 10-3 A

V=30V, R=5.6kΩ I = 30 / 5.6kΩ = 5.36mA