E1 – Electrical Fundamentals # 1 - Atoms and Electrons, Ohms Law, and Resistance

E1 – Electrical Fundamentals

# 1 - Atoms and Electrons, Ohm’s Law, and Resistance

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0 2

Atoms

• Nucleus: the center– Made up of neutrons and protons

• Neutrons– Neutral particles– Neither positive nor negative

• Protons– Positively charged particles

• Electrons– Negatively charged particles– Orbit around the nucleus

8+8n

1 Oxygen atom


Molecules

• Atoms can combine to form molecules


1 Hydrogen atom1 proton 1 electron

1+ 1+

8+8n

1 Oxygen atom8 protons 8 neutrons 8 electrons

1 Molecule of Water

2 Hydrogen

+ 1 Oxygen =H2O

1+

8+8n

1 Hydrogen atom

1 proton 1 electron

1+

Molecules


Positive and Negative Charges

• Balanced charge: electrons equal protons

• Unbalanced charge: allows electrons to flow– Negative charge: more electrons than protons– Positive charge: less electrons than protons


10 Protons and 10 Electrons

“Neutral”

1+ 1+

8+8n

Balanced Charge



“Positive”

1+ 1+

8+8n

Positively Charged Molecule



“Negative”

1+ 1+

8+8n

Negatively Charged Molecule


Conductors

• Free electrons easily leave their orbits

• Materials with free electrons are conductors

• Copper atoms have a free electron


Copper Atom

Nucleus of neutrons and protons

Valence or ‘free’ electron

29 electrons


Current flow in a Conductor

• Free electrons can be forced to move from atom to atom by:

1. Friction – Static electricity

2. Chemical – Batteries

3. Magnetic (induction) - Generator


Copper is a good conductor

Current flow through copper

Empty space attracts free

electron

Voltage knocked electron free


OHM’s Law

• 1 volt will push 1 amp through 1 ohm of resistance• Electromotive force = Intensity x Resistance

E = I x R

E = IR– Electromotive force (E) = Volts– Intensity (I) = Amps– Resistance (R) = Resistance in Ohms (Ω)

Note: E = I x R can also be expressed as

Volts = Amps x Resistance


Using Ohm’s Law Equation

1. E = I x R

(Volts = Amps x Resistance)

2. Solving for I, divide R into E:

E R = I, or

E/R = I3. Solving for R, divide I into E:

E I = R, or

E/I = R


Intro to the Math Behind Ohm’s Law

2 =20 5x

5 5

50 x

You may divide both sides of an equation

by any number (except 0.)

=20 520 x

20=20

=20 5100 x

5


10=amps 5x

The Math Behind OHM’s Law #1

E = I Rx

E = I x RFor example: 10 volts = (2 amps) x (5 ohms)

Solve for I: Solve for amps:552RR

10= ohms2 xE = I RxSolve for R: Solve for ohms:

225II

Solve for E: Solve for volts:E = I x R volts = 2 x 510


10=amps 5x

The Math Behind OHM’s Law #2

E = I Rx

10=2 ohmsxE = I Rx

Solve for I: Solve for amps:

Solve for ohms:Solve for R:

E = I x RFor example: 10 volts = (2 amps) x (5 ohms)

2

5

Solve for E: Solve for volts:E = I x R volts = 2 x 510


What is the voltage supplied to the following circuit?

E = IR

Solve for E (voltage):

E = 5 amps x 24 Ω

E = 5 x 24

E = 120 volts

R = 24 Ω

I = 5 ampsE = ? V

Ohm’s Law Example 1:



E = IR Solve for I (intensity in amps):E R = I120 v 10 Ω = ? amps120 10 = 12 amps

R = 10 Ω

I = ? ampsE = 120 V

What is the current (intensity in amps) in the following circuit?


What is the resistance (ohms) of the load below?

E = IR

Solve for R (Resistance in ohms):

E I = R

120 v .83 amps = ? Ω

120 .83 = 145 Ω

R = ? Ohms Ω

I = .83 ampsE = 120 V



Ohm’s Law Disc

• Using a “disc” is another way to solve the Ohm’s Law equation


E

RII = Intensity

(Amps)

OHM’s Law Disc

R = Resistance(OHMS Ω)

E = Electromotive Force(Volts)


E=I x RR=E

I

OHM’s Law Disc

I=ER

To find Voltage

E

RI

To find CurrentTo find Resistance


ERI

To find Resistance

R =EI

ERI

To find Current

I =ER

ERI

To find Voltage

E =I x R

ERI

E = Electromotive Force(Volts)

I = Intensity(Amps)

R = Resistance(OHMs Ω)

Reviewing OHM’s Law Disc


Calculating Electrical Power

• “Power is the rate at which work is done.”

• Power = Intensity x Electromotive force

• P = IE• Power (watts) = Amps x Volts



Power (watts) = Amps x Volts

Power = Intensity x Electromotive force

P = IEP = 15 amps x 120 volts

P = 15 x 120

P = 1800 Watts

Example 4: What is the power consumption of an electric circuit using 15 amperes and 120 volts?


Power (watts) = Amps x Volts

Power = Intensity x Electromotive force

P = IE solve for IP E = I4800 watts 240 volts = I (amps)

4800 240 = 20 Amps


Example 5: What is the current of an electric heater rated at 4800 watts on 240 volts?


Power = Amps2(squared) x Ohms

Power = Intensity2 x Resistance

P = I2R

P = 52 amps x 10 ohms

P = 52 x 10

P = 25 x 10

P = 250 Watts

Ohm’s Law Example 6:Example 6: What is the power of an electric circuit with 5 amps current and 10 ohms resistance?


Ohm’s Law Wheel

• All applications of Ohm’s Law formulas can be represented as the spokes of a wheel.


P is Power in Watts I is Intensity in Amps

R is Resistance in OhmsE is Electromotive force in Volts

I2 R

P.I

E2

RER P

E

E.I

E2

P

IE

IRPI2

PR

PRPE

IR

Ohms Law WheelOhms Law WheelOhms Law WheelOhms Law Wheel


Resistance & Loads

• Resistance:– Opposition to electron flow in the circuit– Measured in ohms (Ω)

• Loads:– Must have some resistance– Provide a path for electron flow


Compare resistance to crossing a river

• Resistance is the open space between the shores

• Cars represent electrons

• Bridges represent loads

• Without bridges there is no way the cars can cross

• This is known as “infinite” resistance


Go Team!

Infinite Resistance


A load is added

• The load provides a path for electrons

• There is still high resistance to flow

• But it is no longer infinite resistance


Go Team!

But there is still High Resistance

A small load provides a path for some of the electrons


More load is added

• Less resistance

• More electron flow


Go Team!

The resistance is lower

Lower resistance means more electrons, or current flow.


Low or no resistance can be bad

• The lower the resistance,– The higher the electron flow

• If the current flow is out of control, – The circuit is overloaded


Go Team!

Overload

OVERLOAD


Resistance, Watts, and Amps

• Load resistance affects amps and watts

• The lower a load’s resistance,

• The higher it’s amps and watts


Infinite Resistance

∞ Ohms (R)

OPEN

Circuit BreakerTrips

No Watts (P)

No Amps (I)

10 W 1500 Ohms .08 A

100 W 150 Ohms .8 A

8 A 1000 W 15 Ohms

BOOM

L1 N

High Watts & High Amps

0 Ohms

(Note: approximate values in an alternating current 120v circuit)How Resistance affects Amps and Watts


Documents

E1 – Electrical Fundamentals # 1 - Atoms and Electrons, Ohms Law, and Resistance