Module 3.2 Electromagnetism

Volta

Invented the Voltic pile - first battery - (pile of copper & zinc), attached to a wire

Oersted

discovered that electric current produces magnetic field

Faraday

discovered that current is induced by a moving magnetic field

First Law of Electromagnetism

a changing magnetic field induces an electromotive force (EMF) in a conductor

Strength of Magnets

↑ M = ↑ I (current/ amps)

Speed of Motion

↑ S = ↑ I (current/ amps)

Direction of Motion

The way the wire is moved through the magnetic field influences its strength

MOST current

↑ 90^◦

LESS current

↗ 45^◦-50^◦

ZERO current

→ same direction as magnetic field

Shape of Conductor

a.     Straight wire will give some current

b.     Loop coil, will give more

More coils =

More current

↑ _____ = ↑ ____ = more current

turns, loops

Control Magnitude of Induced Current by:

1. Strength of Magnets

2. Speed of Motion

3. Direction of Motion

4. Shape of Conductor

Right thumb rule

when you grab a wire, the way your hand wraps is an indication of the direction the magnetic field is going

Current flows

N to S

Helix

Coil with Wire

Solenoid

Helix with a current

What is a coil of wire?

Helix

What is a coil of wire with a current?

Solenoid

Electromagnet

Solenoid with an iron core

Ferromagnetic material ___ the magnetic strength

↑

2^nd Law of Electromagnetism

the magnitude of the induced EMF is equal to the rate of change of magnetic flux linkage

Lenz Law

o   The induced current flows in the opposite direction of the applied current

o   Called Back EMF (Electromotive Force) or Principle of Self Induction

Self-Induction

The induction of an opposing EMF in a single coil by its own changing magnetic field

Mutual Induction

Magnetic field induces a current in a nearby helix

o  Only in an alternating current

How do we get electricity?

Having a loop of wires being turned

How do Windmills work?

Rotating multiple loop wires through magnetic field

How does the Hoover Dam work?

Turbines create energy with water

How does the San Onofre Power Plant work?

Takes plutonium rods, submerging them into water creating steam. The steam will rise, causing turbines to generate energy

What are Generators?

Converts mechanical energy into electrical energy

Components of a generator

Wire coil between magnetic poles

How does a generator work?

1.      Coil is mechanically turned within field (armature)

2.      As coil moves it cuts through field

3.      Current induced

What are Slip rings?

attached to end of the wires so the wires don’t get tangled up

What does 1 slip ring mean?

→ Direct current

What does 2 slip rings mean?

→ Alternating current

What are Brushes?

Contacts, attached to slip rings when they are stationary while the rings turn to keep the contact with the circuitry

Example if a resistor?

Light bulb

In the US, what is the frequency of an AC generator operator?

60 Hz, 120 alternations

What does a motor do?

Converts electrical energy to mechanical energy

Components of a motor

Same as generator

How do motors operate?

1.      I (current/ amps) is passed through the coil

2.      Magnetic Field of the I interacts with permanent magnetic field causing coil to move

BIG difference between generator and motor:

Motor has a current that is passed through the coil

Types of motors

1. Synchronous

2. Induction

Synchronous motor

a.     coil rotates at same frequency as current (60 Hz)

b.     used in timing circuits in older machines

Induction motor

a.      Stator and Rotor

b.     Uses electromagnets to create magnetic field to interact with current's magnetic field

c.      Type used to rotate anode in an x-ray tube

These wires carry electricity that is ___ voltage but ___ amperage.

HIGH, LOW

↑ V (voltage), ↓ I (current/ amp) → due to

resistance

Types of Transformers

1. Step Up

2. Step Down

Step Up & Step Down - both are

Used to change the magnitude of current & voltage

Transformers operate on the

Principle of Mutual Induction

Step Up

Found in tube circuit (also know as High Voltage Transformer – HVT)

Step Down

Found in filament circuit (used to heat up cathode to boil off electrons)

Transformers Mutual Induction

where the magnetic flux of two or more inductors are “linked” so that voltage is induced in one coil proportional to the rate-of-change of current in another

Transformer Law Voltage

Vp/Vs = Np/Ns

The primary side of a step-up transformer has 500 turns, and the secondary side has 1000 turns. If the voltage on the primary side is 200, what is the voltage on the secondary side? 

X = 400 V

X = 330 V

Transformer Law Amperage

Is/Ip = Np/Ns

V =

Voltage

N =

# turns of the coils

P =

Primary

S =

Secondary

I =

Amperage/ Current

If the number of turns on the primary side is 50 and the number of turns on the secondary side is 150 and the amperage at the input is 10 A, what is the amperage on output?

X = 3.33 I

Transformer Law Amperage formula is

Inversed!

Auto Transformers (SELF) AKA -

The Variable Transformer

Auto Transformers

Able to accomplish Voltage regulation by the Principle of Self Induction

Step Up Transformer =

Mutual induction

Different Auto Transformers

1. Air Core

2. Open Core

3. Closed Core

4. Shell Type

Air Core:

1.      coil & wire

a.      First auto transformer

Open Core:

1.      Adds iron core (bar), inside

a.      Iron core increases the strength of magnetic field

Closed Core:

Inefficient because it still loses energy at the bottom

Shell Type:

1.      Used in the field today

a.      95% efficient

b.     In between the shell is insulated

What type of transformers with two coils of wire?

Air Core

What type of transformer with two coils of wire AND iron bar?

Open Core

What transformer is used in modern x-ray?

Shell Type

List Power Losses

1. Copper (conductor resistance)

2. Hysteresis

3. Eddy Current

Copper (conductor resistance)

↑ distance = ↑ resistance / ↑ cross section = ↓ resistance

Hysteresis

Rearranging magnetic domains

Eddy Current

o   Swirling currents in the core

o   Minimized by lamination of plates

What makes a transformer work?

Alternating Current – A/C

What does the addition of an iron core do to the magnetic field?

increases the strength of the magnetic field

What are some details about the Autotransformer? (voltage, what induction and current, sent to)

incoming line voltage of 110 V/220 V, operates on self-induction with alternating current, sent to the HVT submerged in oil to reduce shock

Why do wires carry electricity that is high voltage, low amperage?

if the voltage is lower, than the amperage will be higher due to the transformers

How does the strength of magnets control the magnitude of the induced circuit?

if the magnetic field increases, the current increases

How does the speed of motion control the magnitude of the induced circuit?

if the speed of the magnetic influence increases, the current increases

How does the direction of motion control the magnitude of the induced circuit?

90 degrees to the magnetic field = the most current

How does the shape of the conductor control the magnitude of the induced circuit?

the more loops the conductor has, the more current

What is an Electromagnet?

a solenoid with an iron core (ferromagnetic material with magnetic strength)

What is the Lenz Law (2nd Law of Electromagnetism)?

the induced current flows in the opposite direction to the applied current, called Back EMF or Principle of Self Induction

What is Self-Induction?

the induction of an opposing EMF in a single coil by its own changing magnetic field

What is Mutual Induction?

a magnetic field induces a current in a nearby helix, only in an alternating current

What are some details about the Autotransformer? (voltage, what induction and current, sent to)

incoming line voltage of 110 V/220 V, operates on self-induction with alternating current, sent to the HVT submerged in oil to reduce shock

What does the addition of an iron core do to the magnetic field?

increases the strength of the magnetic field

What are the three things that cause power loss?

copper is a conductor with resistance hysteresis rearranges the magnetic domain eddy current swirls current in the core, minimized by lamination of plates