E1 – Electrical Fundamentals # 1 - Atoms and Electrons, Ohm’s Law, and Resistance

Atoms Nucleus: the center Electrons Made up of neutrons and protons Neutral particles Neither positive nor negative Protons Positively charged particles Electrons Negatively charged particles Orbit around the nucleus 8+ 8n 1 Oxygen atom © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Molecules Atoms can combine to form molecules © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

8 protons 8 neutrons 8 electrons Molecules 1 Hydrogen atom 1 proton 1 electron 1 Hydrogen atom 1 proton 1 electron 1+ 1+ 1 Molecule of Water 1+ 1+ 8+ 8n 8+ 8n 2 Hydrogen + 1 Oxygen = 1 Oxygen atom 8 protons 8 neutrons 8 electrons H2O © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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

Balanced Charge 10 Protons and 10 Electrons “Neutral” 1+ 8+ 8n © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Positively Charged Molecule 1+ 8+ 8n 10 Protons and 9 Electrons “Positive” © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Negatively Charged Molecule 1+ 8+ 8n 10 Protons and 11 Electrons “Negative” © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Conductors Free electrons easily leave their orbits Materials with free electrons are conductors Copper atoms have a free electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Copper Atom Nucleus of neutrons and protons 29 electrons Valence or ‘free’ electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Current flow in a Conductor Free electrons can be forced to move from atom to atom by: Friction – Static electricity Chemical – Batteries Magnetic (induction) - Generator © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Current flow through copper Voltage knocked electron free Copper is a good conductor Empty space attracts free electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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

Using Ohm’s Law Equation E = I x R (Volts = Amps x Resistance) Solving for I, divide R into E: E  R = I, or E/R = I Solving for R, divide I into E: E  I = R, or E/I = R © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Intro to the Math Behind Ohm’s Law You may divide both sides of an equation by any number (except 0.) 50 x 2 = 20 x 5 100 = 20 x 5 5 5 20 = 20 x 5 5 20 = 20 © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

The Math Behind OHM’s Law #1 E = I x R For example: 10 volts = (2 amps) x (5 ohms) Solve for E: Solve for volts: E = I x R volts = 10 2 x 5 Solve for I: Solve for amps: E = I x R R R 2 10 = amps x 5 5 5 Solve for R: Solve for ohms: E = I I I x R 10 5 = 2 2 2 x ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

The Math Behind OHM’s Law #2 E = I x R For example: 10 volts = (2 amps) x (5 ohms) Solve for E: Solve for volts: E = I x R volts = 10 2 x 5 Solve for I: Solve for amps: E = I x R 10 2 = amps x 5 Solve for R: Solve for ohms: E = I x R 10 5 = 2 x ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Ohm’s Law Example 1: E = IR Solve for E (voltage): E = 5 amps x 24 Ω What is the voltage supplied to the following circuit? R = 24 Ω I = 5 amps E = ? V E = IR Solve for E (voltage): E = 5 amps x 24 Ω E = 5 x 24 E = 120 volts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Ohm’s Law Example 2: E = IR Solve for I (intensity in amps): E  R = I What is the current (intensity in amps) in the following circuit? R = 10 Ω I = ? amps E = 120 V E = IR Solve for I (intensity in amps): E  R = I 120 v  10 Ω = ? amps 120  10 = 12 amps © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Ohm’s Law Example 3: E = IR Solve for R (Resistance in ohms): What is the resistance (ohms) of the load below? R = ? Ohms Ω I = .83 amps E = 120 V E = IR Solve for R (Resistance in ohms): E  I = R 120 v  .83 amps = ? Ω 120  .83 = 145 Ω © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Ohm’s Law Disc Using a “disc” is another way to solve the Ohm’s Law equation © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

E = Electromotive Force OHM’s Law Disc E = Electromotive Force (Volts) E I R I = Intensity (Amps) R = Resistance (OHMS Ω) © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

E R I R= E I I= E R E=I x R To find Voltage To find Resistance OHM’s Law Disc To find Voltage To find Resistance To find Current E R I R= E I I= E R E=I x R © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Reviewing OHM’s Law Disc E = Electromotive Force (Volts) I = Intensity (Amps) R = Resistance (OHMs Ω) E R I To find Voltage E = I x R E R I To find Current I = E R I To find Resistance R = © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Calculating Electrical Power “Power is the rate at which work is done.” Power = Intensity x Electromotive force P = IE Power (watts) = Amps x Volts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Power (watts) = Amps x Volts Power = Intensity x Electromotive force Ohm’s Law Example 4: 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 P = 15 amps x 120 volts P = 15 x 120 P = 1800 Watts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Power (watts) = Amps x Volts Power = Intensity x Electromotive force Example 5: What is the current of an electric heater rated at 4800 watts on 240 volts? Ohm’s Law Example 5: Power (watts) = Amps x Volts Power = Intensity x Electromotive force P = IE solve for I P  E = I 4800 watts  240 volts = I (amps) 4800  240 = 20 Amps © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Power = Amps2(squared) x Ohms Power = Intensity2 x Resistance P = I2R Ohm’s Law Example 6: Example 6: What is the power of an electric circuit with 5 amps current and 10 ohms resistance? 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 © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Ohm’s Law Wheel All applications of Ohm’s Law formulas can be represented as the spokes of a wheel. © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

E is Electromotive force in Volts Ohms Law Wheel E2 R E R P is Power in Watts I is Intensity in Amps I2 R P E IE P R P E I R E .I PR P .I E2 P P I2 IR E is Electromotive force in Volts R is Resistance in Ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Resistance & Loads Resistance: Loads: Opposition to electron flow in the circuit Measured in ohms (Ω) Loads: Must have some resistance Provide a path for electron flow © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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

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

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

But there is still High Resistance A small load provides a path for some of the electrons But there is still High Resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

More load is added Less resistance More electron flow © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

The resistance is lower Lower resistance means more electrons, or current flow. The resistance is lower © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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

If resistance is too low, electron flow will be too high. OVERLOAD © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

Resistance, Watts, and Amps Load resistance affects amps and watts The lower a load’s resistance, The higher it’s amps and watts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

How Resistance affects Amps and Watts (Note: approximate values in an alternating current 120v circuit) OPEN L1 N Infinite Resistance ∞ Ohms (R) No Watts (P) No Amps (I) 1500 Ohms .08 A 10 W 150 Ohms .8 A 100 W 15 Ohms 1000 W 8 A BOOM High Watts & High Amps Circuit Breaker Trips 0 Ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

END OF Atoms and Electrons, Ohm’s Law, and Resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0