Electric 2: Rise of Inductance

Coil

Winding of a conductor into a series of loops to generate an electromagnetic field. Forms an Inductor.

An Inductor is for...

Resisting changes in current flow. (also called Chokes)

The reason an Inductor resists changes in current flow...

Due to a voltage being induced in the inductor whenever current through an inductor is changing.

The Induced voltage...

opposes the source voltage that is creating the current flow.

An inductor resists changes in current because

When the current flowing through it changes, it generates a magnetic field that induces a voltage opposing the change in current, essentially acting like a "back-emf" that tries to maintain the current at its current level;

Inductors are used more then resistors because...

Inductors store more energy and are also better suited to long term applications

Inductance only affects a DC Circuit when...

When the current is first turned on, when its off, or there is a change in the load resistance.

A common application of Inductance...

Is a Car's ignition.

Inductive Reactive Formula

XL(Inductive Reactance in Ohms) = 2 PI f(Hertz) L(inductance)

L

Inductance (Henrys)

F

AC Frequency (Hertz)

5 Factors that determine the amount of inductive resistance an inductor will introduce in a circuit

1. Number of Turns in The Coil (Greater the number of turns, greater the resistance)
2. Diameter of the Coil (Large the Diameter, more resistance)
3. Length of the Coil (longer the Coil, greater the resistance)
4. Type of Core (Iron has more resistance)
5. Frequency of the Alternating Current

Series Inductance Formula

Lt = L1+L2+L3...

Total Series Inductive Reactance Formula

XLT = XL1 + XL2 + XL3...

Total Parallel Inductance Formula

LT = 1/ (1/L1 + 1/L2 + 1/L3)

Henrys (H)

Inductance is measured in ______________________.

Milihenrys (mH)

Henrys are big units, so a milihenry is for smaller units. 1/1000th of a Henry

Total Parallel Inductive Reactive Formula

XLT = 1/ (1/XL1 + 1/XL2 + 1/XL3)

Capacitance

The measure of a device's ability to store electrical energy.

Farad (F)

Unit of capacitance

Microfarads (uF)

0.000001 of a Farad

Capacitor

Device that stores electrical energy

Electrostatic Charge

Stored energy of a capacitor after a voltage source is applied. Voltage increases until it reaches the same as the source voltage.

Capacitors are made when...

Two metal plates are separated with an insulating material

Dielectric

Where the electrostatic charge is stored. A medium or substance that transmits electric force without conduction; an insulator.

Electrostatic charge is stored...

In the Dielectric

C

Mathematic symbol for a capacitor

Three Types of Capacitors

Non-polarized, polarized or electrolytic, variable

Non-Polarized Capacitor

Non polarity sensitive Non-polarized capacitors are big in size with small capacitance. They can be used in both AC and DC circuits.

Polarized or Electrolytic

Polarity Sensitive; used primarily in DC Circuits.

Variable Capacitors

Capacitor values that can be adjusted with a knob

The higher the capacitance...

The more electricity you can store

Capacitors should be...

Discharged before removal. Use a resistor

Two effects a Capacitor has on a DC Circuit

1. Charges a voltage that is equal to the source voltage
2. Acts like an open and does not allow current to flow (HAS TO BE CHARGED)

A DC Voltage applied to a capacitor...

Causes a surplus of electrons on the negative and a shortage of electrons on the positive end. This creates a voltage that opposes current flow. Electrons build upon on the negative side of the capacitor until the voltage across the plates is equal to the source voltage. This means the capacitor has stored a charge.

A charge capacitor...

Can be used as a voltage source for other circuits. It can only supply a short amount however.

Capacitors in a DC environment...

are used in Flash Cameras

The Charged Capacitor

Has the same amount of Voltage as the source voltage because it has the same amount of potential.

Capacitors in AC Current...

are constantly charging and discharging. The load is driven by the charge and discharge current from the capacitor because current cannot flow through the dielectric.

Capacitive Resistance

Measure of a capacitor's ability to oppose changes in voltage direction. Expressed in Ohms

Capacitive Resistance formula

Xc= 1/2pifC

Two factors that effect Capacitive Resistance

1. The Capacitance Value (higher capacitance, lower the reactance and vice versa)

2. Frequency of Current (Higher the frequency, lower the capacitance and vice versa)

Common Applications for Capacitors in AC Circuits

Radio and Audio frequency. The capacitors block unwanted DC signals.

Total Series Capacitance Formula

CT = 1/ 1/c1 + 1/c2 + 1/c3

Total Series Capacitive Reactance Formula

XCT= XC1+XC2+XC3

Total Parallel Capacitance Formula

CT= C1 +C2 + C3

XCT

XCT = 1/ 1/XC1 + 1/XC2 + 1/XC3

Ballast

A type of inductor in Fluorescent lights

A Ballast serves 2 purposes...

1. It delivers a momentary voltage charge that is higher than the source voltage to the lamp, much like a coil in a car's ignition system.

2. Limits the current flowing through the lamp to a predetermined value

Starter

Automatic Switch with low resistance, allowing a high amount of current to go through.

Flip a light switch

The starter turns on (acting as its own switch), but the gas (cathodes) in the lights have high resistance, so the ballast delivers a very high instantaneous voltage, higher than the source voltage. The voltage heats the gas and causes the current to flow, which causes the gas to glow

RC Timing Circuit

Uses a resistor and a capacitor connected in series in a DC circuit to create an electronic timer. This is possible because the capacitor will charge at a specific rate

RC Time Constant Formula

T= R x C

RC Circuit Charge/Discharge Time Formula

TCD = T x 5

T

Time Constant

TCD

Charge or Discharge Time

Time Delay Relays

Use RC Timing to obtain a desired delay before they activate the device(s) they're connected too. Can be adjusted with a knob.

Capacitors and Resistors are often used in DC Electric Power Supplies to

Help create a constant DC Voltage

Rectifier

Apparatus that changes alternating current to direct current

Rectifiers eliminates

The negative cycle of AC input. This causes the voltage pulsates between 0 volts and the peak positive voltage.

The Capacitor

creates a voltage between the pulses

The technique of using a capacitor to smooth out changes in voltage. An inductor can be used to further reduce the ripple because they resist change in current

Filtering

X

Reactance

4 Most Common Electromagnetic devices:

1. Solenoid

2. Buzzer

3. Motor

4. Relay

Solenoid:

Electromagnetic device used to produce linear motion

Buzzer

Electromagnetic device that emits a sound when functioning

Relay

Electromagnetic switch. Consists of a coil and one or more sets of switch contacts.

Motor

Electromagnetic device that produces rotary motion.

Electromagnetism

Magnetism created by the flow of electricity through a wire

Inductance

A property of electromagnetism that opposes any changes in current flow

Inductors in an AC Circuit have a different effect this causes:

Inductive Reactance

Inductive Reactance:

The effect of induction in an AC Circuit. AC electricity constantly resists induced voltage