General: Basic Electricity 🔊 Flashcards
What is the most important law applicable to the study of electricity?
Ohm’s Law
What are the elements of ohm’s law?
Voltage (E), current (l), and resistance (R)
What are four sources of electrical energy?
Thermal, light, pressure, and chemical
What does an electrical circuit consist of?
- A source (battery)
- Resistance or load (light bulbs)
- Conductors (wires)
What represents capacitance in an AC circuit?
A capacitor (same as a condenser)
What is the function of a capacitor?
To store electricity
What is the unit of measure for capacitance?
Farad
What is the standard unit of measure for frequency?
Hertz
What is the basic component that only allows current to flow in one direction?
A Diode (acts like a check valve)
What is inductance?
When voltage is induced by magnetic flux lines in a coil in an AC circuit. The induced voltage is opposite and direction to the applied voltage and opposes any change in the alternating current.
What is an example of an inductor in a magneto?
The coil
What is impedance?
The total opposition for AC to flow caused by the combined effect of resistance, inductive reactance, and capacitive reactance in an AC circuit.
What causes opposition to the flow of current in an AC circuit?
Inductive and capacitance reactance
What is the unit of measurement for impedance?
Ohms
What is the general purpose of a resistor?
To limit current
How may the value of a small, fixed resistor be determined?
By the colored bands on the resistor
What are two things that happen when current flows through a conductor?
A magnetic field is generated and the conductor heats up
What is the common name for the lines of force that make up a field surrounding a magnet?
Magnetic flux lines
What is the concept that describes the relationship between electricity and magnetism?
Electromagnetism
What are the four factors that affect the resistance of an electrical conductor?
The wire gauge, length, temperature, and material
What is the unit of measurement of power in a DC circuit?
Watts. Ampers x volts = watts. 746 watts = 1 horsepower.
What is a kilowatt?
1000 watts
In a DC circuit, what occurs when voltage is increased while resistance remains constant?
There will be an increase in current
What are the three types of DC electrical circuits?
Series circuits, parallel circuits, and complex circuits which are series and parallel circuits.
How many cells does a 24 volt lead acid battery have?
12 cells, with each rated at approximately 2 volts
What are the units that battery capacity is measured in?
Ampere hours
What should be the specific gravity in a fully charged lead acid battery?
It should be between 1.275 and 1.3
What instrument is used to determine the specific gravity of electrolyte in a lead acid battery?
A hydrometer
Why can I hydrometer not be used to determine the charge of a nickel cadmium battery?
The specific gravity of the electrolyte and a nickel cadmium battery does not change appreciably during charge or discharge of the battery.
When using a hydrometer to check the charge of a lead acid battery, at what temperature must correction factor be applied to the reading?
Adjustments must be made if temperature of the electrolyte is above 90° f or below 70° f
What is electromagnetic induction?
It’s the transfer of electrical energy by means of a magnetic field, transferring voltage from one conductor to another without physically touching. This is the principal of transformer operation.
How are battery compartments protected against corrosion?
They are coated with a special corrosion resistant paint such as bituminous paint
What should be the correct electrolyte level in a properly serviced battery?
It should be approximately 3/8 in above the plates. If the battery has baffle plates above the cell plates, the electrolyte level should be up to the holes in the baffle plate on each cell.
What are paralleling generators and how is the load distributed?
This is when two or more generators are operated at the same time to supply power for a load that must be shared equally
Describe no trip or trip free circuit breakers.
A trip free breaker makes it impossible to manually hold the circuit closed when excessive current is flowing. It pops when the circuit gets hot and can’t be reset until it has cooled off.
Can you store ni-cad and lead-acid batteries together?
No, the fumes from the lead-acid battery can contaminate the electrolytes in the ni-cad battery.
What is the result of an imbalance cell in a nickel-cadmium battery?
When a cell has a low internal resistance, the current will increase across the cell causing it to heat up.
What happens to the specific gravity of the electrolyte in a lead acid battery when the temperature changes?
The specific gravity reading on a hydrometer will vary with temperature variations. For example, as the temperature of the electrolyte increases the specific gravity reading will be high. Colder electrolytes will have a lower apparent reading.
What is an LED?
Light emitting diode
What is an SLA battery?
Sealed lead acid battery
What is the basic unit of measurement for inductance?
Henry
What prevents reverse current flow in a DC alternator?
Reverse current cutout
How many wires may be installed on a single terminal lug?
Four
How do you identify wire types?
The lettering on the insulation
Name some functions of a multimeter.
They can read volts, current, and resistance
Name two types of resistors.
Variable and fixed
