Basic Electricity Flashcards
What constitutes a capacitor
two conductors separated by an insulator
What is the purpose of a capacitor
It stores electrical energy in electrostatic fields
Does a capacitor in an AC circuit cause the current to lead or lag the voltage
It causes the current to lead the voltage
The basic unit of a capacitor
The farad
The reason why an electrolytic capacitor can only be used in a DC circuit and not an AC circuit.
They are polarized so they can only work in one direction. If current passes in the opposite direction, it will pass through the capacitor and overheat it (explode)
What is meant by inductuance
The ability to store electrical energy in electromagnetic fields
The basic unit of inductance
The henry
What is an example of an inductor used in a magneto
The primary and secondary coils
Does an inductor in an AC circuit cause the current to lead or lag the voltage
lags
How can you find the polarity of an electromagnet
Hold the electromagnet in your left hand with your fingers encircling the coil int he direction electrons flow (from negative to positive). Your thumb will point to the north pole
What is meant by impedance
Total opposition to current flow in an AC circuit. The vector sum of capacitive and inductive reactance and resistance
What is the basic unit of impedance
Ohm
What are 5 sources of electrical energy
- Light
- Radiation
- Chemical
- Magnetism
- Heat
What is the basic unit of power in a DC circuit
The watt
What is meant by a megawatt
1,000,000 watts
What is the formula for power in a DC circuit
P=IV
The relationship between mechanical and electrical power
1 horsepower= 746 watts
What is meant by true power in an AC circuit
The actual amount of power being used, or dissipated, in a circuit
In what unit is true power expressed in
Watt
What is meant by apparent power in an AC circuit
The combination of reactive power and true power is called apparent power, and it is the product of a circuit’s voltage and current, without reference to phase angle
The basic unit of reactive power
VAR (Volt amps reactive)
What is meant by power factor in an AC circuit
The ratio of true power to apparent power or the ratio of circuit resistance to circuit impedance
What 2 things happen when current flows through a conductor
- Heat is generated
2. Magnetic field surrounds the conductor
The 4 factors that affect resistance of a conductor
- Temperature
- Length
- Cross sectional area
- Material
What is meant by continuity in an electrical circuit
The circuit is continuous so electrons can flow from one terminal to the next
The 3 things that an electrical circuit must have in order to work
- Supply voltage
- Consumers
- Conductors to join the consumers to the supply
What would happen to the current in a DC circuit if length of the conductor doubled but all other factors remained the same?
The current would decrease by half
What is meant by the capacity rating of a lead-acid battery?
The number of hours a battery can supply a given current flow
What is the unit that a battery capacity is expressed in
Ampere-hours
What electrolyte is used in a lead acid battery
Sulfuric acid and water
Does the specific gravity of the electrolyte in a lead-acid battery increase or decrease as the battery becomes discharged
Decreases
What is the specific gravity of a fully charged lead-acid battery?
1.275 - 1.300
How many cells are there in a 24-volt lead acid battery
12
What is the range of temperature of the electrolyte in a lead acid battery that does not require a correction when measuring its specific gravity
70-90F
What instrument is used to measure the specific gravity of the electrolyte in a lead acid battery
A hydrometer
How doe you treat a lead acid battery compartment to protect it from corrosion
paint it with asphaltic paint or polyurethane enamel
What is used to to neutralize spilled electrolyte from a lead-acid battery?
mixture of sodium bicarbonate and water
Why is the closed-circuit voltage of a lead acid battery lower than its open circuit voltage
There is a voltage drop across the battery
What is the open-circuit voltage of a lead acid cell
2.1 volts
What gases are released when a lead acid battery is being charged?
hydrogen and oxygen
What precautions should be taken in the maintenance shop where both lead acid and nickel-cadmium batteries are serviced?
They should be kept separate and tools for servicing them should be kept separate
What is the electrolyte used in a nickel-cadmium battery
Potassium hydroxide and water
Why is a hydrometer not used to measure the state of charge of a nickel-cadmium battery?
The SPG does not change since there are no chemical changes that occur when the battery is being discharged or charged
The lowest level of electrolyte in a nickel-cadmium battery occurs when
when the battery is fully discharged
What is the result of cell imbalance in a nickel-cadmium battery?
Low internal resistance which leads to higher current flow between the unbalanced cells which leads to high heat
What is thermal runaway?
Low internal resistance increase the rate of internal heat generation exceeds the rate at which the heat can be expelled. The battery temperature increase until the cells dry out and the container softens, breaks and melts.
How can thermal runaway be prevented?
Carefully monitor the temperature of the middle cells and controlling the charging current
How is it possible to know when a nickel-cadmium battery is fully charged?
Completely discharge the battery and give it a constant-current charge to 140% of its ampere-hour capacity
What is used to neutralize spilled electrolyte from a nickel-cadmium battery?
Solution of boric acid and water
EMF is measured in what?
Volts
What are the 3 effects of electrical current?
- Heating effect
- Magnetic effect
- Chemical effect
4 factors affecting electrical resistance
- Length of wire
- Type of material
- Cross section
- Temperature
Kirchoff’s First Law states:
Total current flow into one point on a circuit, is equal to the current flow out of that point
Kirchoff’s Second Law states:
If all voltage drops in a closed circuit are added up, the sum equals the total applied voltage
