MElec-Ch1 - 1

1
Chapter 1

• Properties
• of
• Electricity

2
Overview

• What is Electricity
• Ohms Law
• Boat Circuit Problems
• Multimeters
• Magnetic Lines of Force

3
What is Electricity

• Electricity consists of electrons
• Negatively charged
• Electrons actually flow from negative to positive
• Current flow, by convention, from positive to
  negative
• Conductors have electrons that readily move
• e.g. silver, copper, metal and liquids (salt
  water)
• Insulation has tightly bonded electrons
• Charges do NOT move
• e.g. plastic, rubber, glass and ceramics

4
Water Analogy

• Height of water Voltage
• Valve Switch
• Water wheel Electric motor
• Small pipe Resistance

5
Electrical Circuits

• Simple Series Circuit
• Same current flow through all devices

6
Complex Series Circuit

• If one light bulb burns out
• No lights will be on
• Therefore, not used for light circuits

Off
Off
7
Complex Parallel Circuit

• If one light bulb burns out
• Other will remain on
• Therefore, used for light circuits

On
On
8
Ohms Law

• E Voltage (pressure) in volts
• I Current (rate of flow) in amperes
• R Resistance (friction) in ohms
• P Power (work) in watts
• E I R R E / I I E / R
• P I E P I2 R P E2 / R

E
I
R
9
Practice (fig 1-5)

• Given 12 volts and 4 amps
• What is resistance?

E I R
R E / I
R 12 / 4
R 3 ohms (or 3 ?)
12 VDC
4.0 Amps
10
Practice (fig 1-6)

• Given 12 volts and 8 ohms
• What is current?

RT R1 R2
E I R
I E / R
I 12 / 8
I 1.5 amps
4 ohms (each)
12 VDC
11
Practice (fig 1-8)

• What is current in each device?

6 amps in 2 ohms
2 amps in 6 ohms (each)

• What is total current?

IT I1 I2 I2
IT 10 amps
12 VDC
12
Electrical Power

• Watt is unit of electrical power
• Given 12 VDC and total resistance of 6 ?
• What is total power?

I E / R
I 12 / 6
I 2 amps
P E I
P 12 2
P 24 watts
13
What We Have Learned So Far

• Electricity is the negatively charged electrons
  that have been freed from the structure of an
  atom
• For electricity to perform some useful function
  it must flow in a circuit
• There are two basic types of electrical circuits
• The Series Circuit
• The Parallel Circuit
• Using Ohm's Law we can calculate the three
  electrical values in a circuit, i.e. Voltage,
  Amperage, and Resistance
• The fourth electrical value is Power
• Power is measured in Watts
• Using the PIE equation we can calculate Power
• Using Ohm's Law and PIE equation if we know any
  two values we can find the other two

14
Boat Circuit Problems

• Open Circuit is break in electrical wiring
• Current flow (path) is interrupted
• Sometimes deliberately by switch
• Short circuit is electrical wiring shortened from
  original length
• Shorts to ground
• Interwiring short
• Internal short

15
Multimeters

• Used to measure
• Voltage
• Current
• Resistance
• Types of Multimeters
• Analog
• Digital
• Preferred
• Easier to read

16
Measuring Voltage

• Voltage to DC
• Range to 20 volts
• Red lead to positive
• Black lead to negative
• Meter across load
• Parallel with load
• Battery voltage is 12.6

17
Measuring Voltage at Light

• with good fuse
• and switch On
• Should measure approx.
  12 VDC at each light

18
Measuring Voltage Drop

• Across a closed switch
• Should measure zero volts
• Across a high resistance connection
• Should measure a voltage drop

19
Measuring Current

• Current to DC
• Range to 10 amps
• Red lead to current jack on multimeter
• Insert meter in series with circuit

When measuring voltage - meter is across the load
20
Measuring Resistance

• Function to resistance
• Touch test leads together
• Adjust resistance to zero (0.0) ohms
• Place test leads across device to be measured
• Continuity measurement
• When test leads are across low resistance
• (Good circuit or device)
• Will hear a buzz indicating continuity

21
Magnetic Lines of Force

• Results of Electrical Current
• Heat (due to resistance in wire)
• Chemical reaction (in current carrying solution)
• Magnetic Field (illustrated)

22
Remote Control Circuit
Small current through solenoid coil - Controls
larger current, through contacts,
to Starter Motor
23
Summary

• Electricity is negatively charged electrons
• Current flows from positive to negative
• Types of circuits
• Series (one path for current flow)
• Parallel (multiple paths for current flow)
• Ohms Law
• E I R
• P E I
• Boat Circuit Problems
• Open Circuits
• Short Circuits

24
Summary - 2

• Multimeter
• Digital preferred
• Measure voltage across (parallel to) load
• Can also measure voltage drop
• Measure current in series with load
• Magnetic Lines of Force
• Concentrated in coil
• Solenoids use in remote control circuits
• Small current controls large current