Introduction to Engineering ENGR Electrical Engineering. Dr. Coates

Transcription

1 Introduction to Engineering ENG Electrical Engineering Dr. Coates

2 Branches of Electrical Engineering Circuits/Microelectronics Communications Computer Hardware and Software, Digital Logic, Microprocessor design (Computer Engineering) Control Systems Power obotics Semiconductor design/fabrication Signal Processing VLSI

3 Electrical Circuits An electric circuit or circuit is an interconnection of electrical elements (components) Elements have terminals (often two) and are described mathematically in terms of voltage and current

4 Current and Charge Current is the charge passing through an area in a unit of time The basic unit of charge is the Coulomb and the basic unit of current is the Ampere (A)

5 Current and Charge Current can flow in a circuit if there is a closed path DC (direct current) is current of constant magnitude. AC (alternating current) is a particular type of time varying current (sinusoidal)

6 Current and Charge Current i 1 is due to charge flow from terminal a to b i 1 Current i 2 is due to charge flow from terminal b to a a Z b i 2

7 Voltage Voltage is proportional to the work (energy) required to move charge between two terminals of an element The units of voltage are Volts (V).

8 Voltage Voltage is measured ACOSS the element v ab Voltage v ab is proportional to work required to move a unit of charge from terminal a to b a Z v ba b The voltage v ab is referred to as voltage drop from a to b or the voltage at a with respect to b

9 esistance esistance is a measure of how easy or difficult it is to move charge through a material The units of resistance are Ohms (Ω). Aluminum, copper, gold, and silver (along with most metals) are good conductors (low resistance)

10 esistors An element with resistance is called a resistor The voltage drop across a resistor can be related to the current flowing through the resistor by Ohms Law v i

11 Sources Sources supply energy to circuits Practically the function specifying the source changes, for instance the energy that a battery can supply degrades as it is used.

12 Electric Circuits Consider the following circuit consisting of a single source (10V battery) and a load (resistor) If the voltage drop across is v 10V and 1000Ω, i v/ 0.01A

13 Series Circuits A series circuit consists of a source in series with one or more elements A series circuit is a circuit with a single loop. Vs 4 V Ω i1 i2 is Ω

14 Series Circuits The current flowing through each element in a series circuit is the same Vs 4 V Ω i1 i Ω The total resistance "seen" by the source in a series circuit is the sum of the individual resistances, is i i i s i 1 2 total Ω

15 Series Circuits Once we know the total resistance of the circuit, we can use Ohms law to find the current through each element Vs 4 V Ω i1 i2 is Ω i V s total A

16 Series Circuits Once we know the current through each element, Ohms law can be used to find the voltage across each element Vs 4 V Ω i1 i Ω is ( 0.001) 1000 V V i ( 0.001) 3000 V V i 3 2 2

17 Analyzing Series Circuits Find the total resistance seen by the source (several series resisters can be replaced by a single equivalent resistor) total k k Find the current in the circuit (same for all elements) i V s total Find the voltages across each element using Ohms law v i

18 Example Find the voltage across 1 and 2 in the circuit shown. i --> Vs 5V 3000Ω Ω

19 Given : v V v v 1 total s 3000Ω? i i i v Solution : total? i v v 5000Ω 8000Ω V s total Example V s 5V What is the current flowing through the circuit? 5V 8000Ω What are the voltage drops across the resistors? A 3000Ω 1.875V A 5000Ω 3 A 3.125V

20 Example Find the voltage across Ω i Vs 9 V Ω Ω

21 Given : V v Ω 9V? Solution : V s s total i 1 total i 300Ω Ω v2 i2 0.15A 300Ω 3 V s total Example 4.5V 200Ω Find the current flowing through the circuit : 9V 0.15A 600Ω Now what is the voltage drop across resistor 2?

22 Parallel Circuits A parallel circuit consists of a source in parallel with one or more circuit elements Vs 5 V is i1 i Ω Ω

23 Parallel Circuits The voltage across each element in parallel is the same as the source voltage Vs 5 V is i1 i Ω Ω The current in each branch of the circuit can be found using Ohms law Vs 5 i A Vs 5 i A

24 Parallel Circuits The current supplied by the source is the sum of the currents in the other branches Vs 5 V is i1 i Ω Ω i s i 1 + i A A 0.015A

25 Analyzing Parallel Circuits Voltage across each branch element is same as source Find the current in each branch using Ohms law Find the current supplied by the source V s i v 1 v2 v i s i k k...