Theory Flashcards
What is ohm’s law?
Current is directly proportional to the voltage and inversely proportional to the resistance of the circuit.
E= I x R. I = E/R. R=E/I
What are the Advantages of a 3 wire Edison system?
2 different voltages
Uses Less conductor material
Less line loss
Using ohm’s law, how would you find E?
E = I x R
In a series circuit, the current ( I ) is directly proportional to the resistance of the circuit.
True or False?
False……. The current ( I ) is inversely proportional to the resistance of the circuit.
What is coloumb?
A coulomb represents a quantity of charge provided by a massive number of electrons. Approximately
6.28 x 10>18 of them.
What is the unit of measurement for charge? What is it’s symbol
Coulomb’s….. The unit symbol is C
Describe the equation:
I = Q/T
Current = Quantity of charge / unit of time.
What is kirchoff’s current law as it applies to a parallel circuit?
All current values entering a junction point must equal all currents leaving the junction point.
What is another name for a parallel circuit?
A branch circuit
Lights and receptacles are almost always connected to what type of circuit?
A branch circuit ( parallel circuit )
Describe a parallel circuit.
A circuit with more than one path.
The total resistance of a parallel circuit is always less than he resistance of the smallest branch.
True or False
True
Describe current
The flow of electrons between two points from negative to positive.
What is resistance?
The opposition to flow.
What is charge?
A build up of electrons.
What is voltage?
A potential difference in charge.
What are the three basic properties of an electric circuit?
Current, voltage ( emf ), resistance.
What is the name of the force that maintains a voltage?
Electro-motive force.
When a fifth resistor is added in parallel to four parallel connected resistors, what happens to the total current?
The current increases
When a fifth resistor is added in parallel to four parallel connected resistors, what happens to the total resistance ?
The Resistance decreases.
In a series circuit, the voltage drop is directly proportional to the resistance rating.
True or False
True
List six methods for producing emf.
Magnetic/Mechanical Static/Friction Pressure/Piezo Electric Effect Light/Solar ( photo voltaic cells) Heat (furnace, thermocouples) Chemical (Batteries)
Describe the basic structure of an atom.
A nucleus containing protons and electrons.
Name the two main particles in the venter of an atom.
Protons and neutrons.
What makes up the nucleus of an atom?
Protons ( + ) and neutrons ( -/+ )
Name the particles that rotate in orbit of the atom.
Electrons ( - )
Materials with a low resistance are known as……
Conductors
Materials with a high resistance are known as…….
Insulators
What is kirchoff’s voltage law as it applies to series circuits?
The sum of the voltage drops must equal the total applied voltage.
E = V1 + V2 + V3…….
Or
E - V1 - V2 - V3 = 0
What is kirchoff’s voltage law as it applies to a series-parallel circuit?
The sum of all voltages in a closed loop must equal applied voltage.
Kirchoff’s current law as it applies to a series parallel circuit.
The sum of current(s) entering a junction must equal the sum of the current(s) leaving that junction.
It = I1 + I2 + I3…….
What is kinetic energy?
What is potential energy?
Kinetic energy is energy stored in the motion of objects.
Potential energy is energy stored by the position of objects.
An object has potential once the object starts moving it becomes kinetic energy.
What is mass?
What is mass measured in?
The measurement of an amount of substance contained by an object.
Mass is measured in kilograms.
What is force? What is it measured in?
Force is a directional push or pull required to change an object.
Force is measured in newtons.
What is force measured in?
Newtons
What is weight?
Weight is the measurement of force to equal the force of gravity that exists between two masses.
Measured in newtons of force but is commonly described in kilograms.
What’s the difference between mass and weight ?
Mass never changes, weight can change due to force.
What is work?
Work is the application of a force to an object to change it’s motion.
Work = force( n ) x distance( m )
Work is measured in joules.
1 n • m = 1joule( j )
What is energy ?
What is the unit of measurement for energy?
Energy is the capacity to do work.
Electrical is measured in joules.
J = C x V
What is power?
What is the unit of measurement of power ?
Power is the rate of doing work.
Power is measured in watts, P = I x V
What is the relationship between work, power and energy?
Work is done when a force causes motion.
When Force is used to lift or move a mass, work is done.
The faster the mass is moved the greater the power.
P = work/time
How many watts are in 1 horsepower motor?
746 W = 1hp
Electrical energy is measured by what unit?
A kilowatt-hour ( kWh )
1kWh = kJ/s x time (s)
The basic material used for the electrodes in Leclanché cell are?
Carbon and zinc
What is the electrolyte paste in a Leclanché dry cell?
A mixture of zinc chloride and ammonium chloride.
What is the open circuit value of a Leclanché cell?
1.5 V
What electrolyte is used for a primary alkaline dry cell?
Potassium hydroxide and water.
What are the 3 types of lead acid batteries?
Flooded cell
Gelled electrolyte cell
Absorptive glass mat. ( AGM )
What is faraday law of induction?
If the current in a conductor hanged, the magnetic field around that conductor changes proportionally.
What is Lenz’s law?
Induced voltage will cause a current flow in such a direction that it’s magnetic effect will oppose the change that produced it.
What is self induction
When a change of current in a circuit causes a change in the magnetic field, inducing voltage back into that circuit.
What is an electro magnet?
A magnet created by energizing of a coil.
Magnetic moments align to form what?
Domains
What is flux?
Lines of magnetic force.
What is retentivity?
Ability to retain magnetism
What is permeability ?
The ability to concentrate magnetic lines of flux.
What is saturation?
When maximum magnetism of a material is reached.
