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Electrical Engineering
Chapter 15
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Terms in this set (38)
What is the correlation between electricity and electronics?
Electricity powers electronics
What is electricity?
The movement of electrons from a more negative atom to a more positive atom at the speed of light
What do you need for a continuous flow of electrons? (Hint: 3 things)
•an excess of electrons in one place
•a lack of electrons in another place
•a path between the two places
What are the two types of power sources in an automobile and an example of each?
•chemical reaction (car battery)
•magnetism (alternator)
What is induction?
The production of electricity through magnetism
How does an alternator work?
A magnetic field - driven by the crankshaft via the drive belt - rotates through a coil of wire, producing electricity which restores electrons in the battery
What is current and how is it measured?
-The movement or flow of electricity
-more electrons=more current
-measured in amps
What is the difference between AC & DC?
DC (direct current) electrons move in one direction, whereas AC (alternating current) the electrons change direction at a fixed rate
Technician A & Technician B are discussing current. Technician A says that DC is most common for automotive work. Technician B says that current flow moves from a point of lower voltage to a point of lower voltage. Who is correct?
A only. Current flow moves from higher voltage to lower.
What is voltage and what are other terms for it?
-the potential difference between two points
-the force developed by the attraction of electrons to protons
-electrical pressure
-electromotive force (EMF)
*measured in volts
Which substances meet resistance when they flow?
All/any
What is produced from the resistance to current flow?
Heat
What unit measures resistance?
Ohms
How would AC voltage appear on a graph and what does it show?
As a sine wave, which shows the current changing in strength and direction
What is "peak-to-peak" value?
The movement of AC from the positive peak to the negative peak back to the positive peak
How are AC volts measured?
By the difference between the peak positive and peak negative value
What does DC look like on a graph?
A flat line
Technician A & Technician B are discussing Alternating Current. Technician A says that AC has 29% less heat than DC. Technician B says that AC volts are never expressed as root mean square values (RMS). Who is correct?
A only, AC volts are OFTEN expressed at RMS values.
What happens to current as voltage changes in value and direction?
It changes too. The change of current is "in phase" with the change in voltage, which means the two sine waves go through their max and min peaks at the same time and in the same direction.
Describe closed and open circuits.
-Closed (completed) circuits have a continuous path from the positive and negative of a power source. They have continuity.
-Open (incomplete) circuits have a break in the path where current cannot flow through the whole circuit
What is an electrical load?
A component that uses electrical power to control the current and convert electrical energy into another form of energy.
How are loads shown on electrical diagrams?
As a symbol representing the part or as a resistor (zig zag line)
Describe what happens to current as resistance changes?
As resistance goes up, current goes down. As resistance goes down, current goes up.
What shows the energy or voltage needed to allow current to flow through a load?
Voltage drop
Two technicians are discussing circuits. A says that voltage stays the same as it moves through a load. B says that amperage goes down as it moves through a load. Who is correct?
Neither. Amperage remains constant but voltage drops as it moves through a load.
Define power and what it is measured in.
-the rate of doing electrical work, or the rate at which electrical energy is converted to another form of energy
-expressed in watts
What is the formula for finding watts (power)?
-Volts x Amps = Watts
-Current x Voltage = Power
What do most automotive electrical circuits use as a conductor for the negative side of the battery and why is this efficient?
The chassis. Using the frame as a return path or ground eliminates the need for a separate ground wire at each component.
Explain Ohm's Law.
It takes 1 volt of electrical pressure to push 1 ampere of current through 1 ohm of resistance. V = O x A
Explain a simple electrical circuit.
A load connected to a voltage source by conductors
Two technicians are discussing voltage drop. A says only some voltage is dropped through a circuit. B says voltage drop can be calculated using Ohm's law. Who is correct?
B only. All of the voltage is dropped to the loads in a circuit as electrical energy is changed to another form of energy.
Are electrons consumed as work is performed?
No, but the force on the electrons is reduced (voltage drop).
What is another word for resistance?
Impedance
What happens to watts when resistance increases?
It decreases.
If you have a circuit with 12 Volts and 6 Ohms of resistance, how do you find the watts?
Watts = Amps x Volts and we don't know the Amps yet so we have to find Amps.
Amps = Volts / Ohms so 12/6=2 Amps
Watts = 2 x 12 = 24 Watts
What types of energy can electrical energy be converted into? (Hint: 4 types)
-sound
-heat
-light
-motion
What are the basic parts of automotive electrical circuits, what do they do, and what is an example of each? (Hint: 5 parts)
-power sources (battery or generator) which provide the energy needed to cause electron flow
-conductors (copper wires) which provide a path for current flow
-loads (light bulbs, electric motors, or resistors) which are devices that use electricity to perform work
-controllers (switches or relays) which control or direct the flow of electrons
-circuit protection devices (fuses, circuit breakers, or fusible links) which protect the circuit from damage when overloaded or shorted
What are the three basic types of automotive electrical circuits?
series, parallel, and series-parallel
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