Basic ElectronicsLecture#3

RESISTORS/Capacitors

By: Engr. Muhammad Adnan Malik

Class of BS.IT, ISP

Series and Parallel Combinations of Resistors

• Series Combination

• Parallel Combination

Proper ties of Series Combinations of Resistors

•In Series combination of resistors current across each resistor is same •In Series combination of resistors, voltage across each resistor voltage is different.

Proper ties of Series Combinations of Resistors

Properties of Parallel Combinations of Resistors

•In Series combination of resistors current across each resistor is different.• In Series combination of resistors voltage across each resistor is voltage is same.

Properties of Parallel Combinations of Resistors

Total resistance in Series

Total resistance in series

•When Resistance are in series, total resistance is gives by:

Total resistance in Parallel

Warm Up Yourself!! Series Circuit

Series Circuit

•Two resistances R1 and R2 of 5ohm each and R3 of 10ohm are in series. How much is Rt ? With 80 V applied across the series string of resistors, how much is the current in R3 ?

RT =R1+R2+R3 =5 +5 +10 Rt=20 I =Vt/Rt= 80/20 I =4 A

Power In R3?P=640 W

Parallel Circuit

Parallel Circuit

Both Series & Parallel Circuit

Both Series & Parallel Circuit

Both Series & Parallel Circuit

Kirchhoff ’s Voltage Law (KVL)•Kirchhoff’s voltage law states that the sum of all resistor voltage drops in a series circuit equals the applied voltage. •Expressed as an equation, Kirchhoff’s voltage law is

VT =V1 +V2 +V3

Kirchhoff ’s Current Law (KCL)•Kirchhoff’s current law (KCL) states that the total current It in the main line of a parallel circuit equals the sum of the individual branch currents.•Expressed as an equation, Kirchhoff’s current law is

It = I1 +I2 I3

KVL-An Example•A voltage source produces an IR drop of 40 V across a R1=20ohm , 60 V across a R2=30ohm , and 180 V across a R3=90ohm , all in series. According to Kirchhoff’s voltage law, how much is the applied voltage V T ?

Vt=40+60+90=280V

KCL-An Example•An R1 of 20 ohm , an R2 of 40ohm , and an R3 of 60ohm are connected in parallel across the 120-V power line. Using Kirchhoff’s current law, determine the total current It

KCL-An Example

Capacitors• Definition: A capacitor is an electronic device that stores

an electrical charge between the two plates• A basic capacitor has two parallel plates separated by an

insulating material• The unit of capacitance is Farads (F)• Capacitance values are normally smaller, such as µF, nF

or pF

Different Types Of Capacitors

Reading Values of capacitance Of Capacitors

Storing a charge between the plates

• Electrons on the left plate are attracted toward the positive terminal of the voltage source

• This leaves an excess of positively charged holes

• The electrons are pushed toward the right plate

• Excess electrons leave a negative charge + -

+ _+ _

Working Of Capacitors

Working Of Capacitors

What is dielectric?

The Farad Unit of Capacitance

• With more charging voltage, the electric field is stronger and more charge is stored in the dielectric.

• The amount of charge Q stored in the capacitance is therefore proportional to the applied voltage. Also, a larger capacitance can store more charge. These relations are summarized by the formula:

Q =CV coulombs

Example•How much charge is stored in a 2uF capacitor connected across a 50-V supply?

Q =CV =(2u)x50=100 uC

•A constant current of 2 uA charges a capacitor for 20 s. How much charge is stored?

Q =Ixt=2u x 2=40 C

Some Properties Of Capacitor

• Allow AC current to pass.• Stop DC current.• Stores Voltage in the form of electric field.• Capacitors in series:

1/Ct=1/C1+1/C2...• Capacitor In Parallel:

Ct=C1+C2+C3...