Practice Questions: Electromagnetism, Transformers, & Generators
10,000 Gauss = ______ Tesla
1 Tesla
Designed to permit electron flow in one direction only.
Diode
The material of choice for semiconductors is a. silicon b. carbon c. gadolinium d. ferrous iron
a. silicon
What is the primary element in semiconductors? a. Phosphorus b. Boron c. Silicon d. Tungsten
c. Silicon
Ratio between field strength and area.
magnetic flux
Also called an SCR
Thyristor
True or False: An AC generator produces a current that is expressed mathematically as a sinusoidal wave.
True
True or False: Mutual induction occurs when two coils (not connected) are supplied with alternating current, causing current to flow in the secondary coil.
True
True or False: The efficiency of a transformer is not affected by the transformer turns ratio.
True
True or False: The resistance experienced by the flow of electrons with alternating current in a coiled loop of wire by an opposing current is called impedance.
True
Obsolete type of rectification technology.
Valve tube
An autotransformer only has one: a. Coil b. Meter c. Rectifier d. Switch e. Turns ratio
a. Coil
An electron doper to improve conductance.
arsenic
Which of the following regulates the amount of induced current in a conductor? 1. Speed at which the magnetic field cuts the conductor 2. Strength of the magnetic field 3. Angle at which the magnetic field cuts the conductor. a. 1 and 2 b. 1, 2, and 3 c. 1 and 3 d. 2 and 3
b. 1, 2, and 3
The second digit of the left hand motor rule represents a. The direction of the wire b. The direction of the magnetic flux c. The direction of the current in the wire d. The direction the armature will move
b. The direction of the magnetic flux
An electrical device that is designed to store charge momentarily after charging is a/an a. battery b. capacitor c. thyristor d. dielectric
b. capacitor
The direction of current flow in the solid state rectifier is: a. from n-type to p-type silicon b. from p-type to n-type silicon c. current may flow in either direction d. this will depend on how the rectifier is connected
b. from p-type to n-type silicon
How long does it take for the completion of one half of a sine wave representing 60 Hz of current? a. 60 seconds b. 1 second c. 0.0083 second d. 0.016 second
c. 0.0083 second We know that a sine wave (such as AC current has) has 2 changes of direction per wave - one on the top, and one inverted on the bottom. It makes 60 changes in 1 second with 60 Hz. So: 1 second / 60 changes = 1/60 second per single wave Divide that by half to see what half the wave would be...as a decimal that's 0.0083_
Which of the following conditions can occur during electromagnetic induction? 1. magnetic lines of force are cut by a conductor 2. a conductor is cut by magnetic lines of force 3. a magnetic field is induced in the conductor a. 1 only b. 2 only c. 1 and 2 only d. 1, 2, and 3
c. 1 and 2 only Choice 3 is backwards - current is induced in the conductor, not magnetism!
American generators operate at a. 220 V b. 120 AC c. 60 Hz d. 30 A
c. 60 Hz
Opposing voltage created in a conductor by passing alternating current through it describes: a. Electromagnetism b. Electrodynamics c. Self-induction d. Mutual induction
c. Self-induction All transformers use AC, but this best describes an autotransformer because mutual induction also involves two conductors being places near one another in order for current to be induces in one due to flowing in the other. With self-induction, this is caused by the current itself, due to the configuration of the coils.
The middle finger of the right hand motor rule represents: a. The direction of the wire b. The direction of the magnetic flux c. The direction of the electron flow or current in the wire d. The direction the armature will move
c. The direction of the electron flow or current in the wire
Inducing current flow in a secondary coil by varying the current flow through a primary coil describes: a. Electromagnetism b. Electrodynamics c. Self-induction d. Mutual induction
d. Mutual induction
A coiled current carrying conductor with a ferromagnetic core is called a(an): a. helix b. solenoid c. magnet d. electromagnet
d. electromagnet
A stator consists of a. bars of copper around an iron core b. commutator rings c. a rotor d. electromagnets
d. electromagnets
An electrical coil with ferrous and area.
electromagnet
What classification of magnet is cobalt?
ferromagnetic
Atomic element that creates electron "holes".
gallium
Resistance to demagnetization.
retentivity
P-type material that creates electron "holes".
semiconductor
Electron rotation on a magnet.
spin magnetic moment
The N-type Silicon has been laced or treated with: a. Gallium b. Arsenic c. Silver d. Bromide
b. Arsenic
True or False: Mutual induction occurs when two coils are connected in series, causing current to flow in the secondary coil.
False
What type of atoms are mixed in with the p-type semiconductor? a. Phosphorus b. Boron c. Tungsten d. Lead
b. Boron
True or False: Fleming's hand rules are based on electron flow.
False
True or False: In a diode made of p-type and n-type semiconductors meeting at a junction, an electron current can flow in either direction.
False Diodes only allow flow from positive to negative.
In the design of the autotransformer: a. A single coil serves as both the primary and the secondary coils b. The exposure time is on the primary side c. The major kVp adjustment is on the primary side and the line compensator are on the secondary side d. The major kVp adjustment is on the primary side and the minor kVp adjustment is on the secondary side e. There are separate primary and secondary coils
a. A single coil serves as both the primary and the secondary coils
A transformer will operate on which of the following? a. Alternating current only b. Direct current only c. Alternating and direct current d. Batteries only
a. Alternating current only
A rectifier: a. Can be a semiconductor b. Converts DC to AC c. Increases current d. Increases voltage e. Increases x-ray intensity
a. Can be a semiconductor
As described by the left hand generator rule, the index finger represents: a. Direction of the magnetic flux b. Direction of the flowing electrons c. Direction of conventional current flow d. Direction the conductor is moving in the magnetic field
a. Direction of the magnetic flux
What generates the heat to which much of the energy of a vacuum tube is lost? a. Filament b. Anode c. Transformer d. High-voltage wires
a. Filament
Free electrons are: a. Found in n-type semiconductors b. Found in p-type semiconductors c. Emitted from diodes. d. A property of silicon.
a. Found in n-type semiconductors
A coiled current carrying conductor is called a(an): a. helix b. solenoid c. magnet d. electromagnet
b. solenoid
Which of the following transformers operate by electromagnetic mutual induction? 1. autotransformer 2. Choklin transformer 3. step-up transformer 4. step-down transformer a. 3 and 4 only b. 2 and 3 only c. 2, 3, and 4 only d. 1, 2, 3, and 4
a. 3 and 4 only
What do full-wave rectifiers use to convert an alternating current into a direct current? a. Four rectifiers b. Two alternating rectifiers c. Direct-current generator d. Single-phase generator
a. Four rectifiers
A vacuum tube rectifier works by allowing current to flow through it in: a. One direction b. Both directions c. Alternating directions d. It depends on the circuit using the rectifier
a. One direction
What charge does the hole, or absence of an electron, have in the p-type semiconductor? a. Positive b. Negative c. Neutral d. None
a. Positive "P" for positive!
Which of the following has four electrons in its outer shell? a. Silicon b. Boron c. Phosphorous d. All of the above
a. Silicon
The simplest type of current; voltage (and accompanying current) flows as a sine wave; voltage begins at zero, peaks at full value at the crest of the wave, returns to zero, reverses, and again peaks on the inverse portion of the cycle at the trough. This describes: a. Single-phase, two pulse alternating current b. Three-phase alternating current c. High-frequency current d. Direct current
a. Single-phase, two pulse alternating current
The major difference between a solenoid and an electromagnet is that the electromagnet has: a. an iron core b. a coiled conductor c. a current carrying conductor d. a permanent magnetic field
a. an iron core
Which of the following is a component of a tube-type rectifier? a. filament b. magnetic core c. primary windings d. secondary windings
a. filament
A transformer with more secondary windings than primary windings a. has a greater secondary voltage b. is a step-down-transformer c. has a greater power output than input d. has a higher power loss
a. has a greater secondary voltage
If the number of turns of wire in the secondary coil is twice the number in the primary coil, the voltage in the secondary coil is: a. increased by two times b. increase by four times c. decreased by two times d. decreased by four times
a. increased by two times Remember, this is a direct formula - so double the turns, double the voltage.
The inherent power loss of electrical conduction through solid wire conductors a. is minimized with higher voltage transmission b. has no relationship with current flow c. results from space charge d. is lower with current flow rather than electron flow
a. is minimized with higher voltage transmission
In a step-up transformer, the current in the secondary winding is _______ than the primary winding. a. less b. more
a. less
What is produced if boron atoms are mixed in with silicon atoms? (Boron atoms have three electrons in their outer shell.) a. p-type semiconductor b. n-type semiconductor c. Any semiconductor d. None of the above
a. p-type semiconductor
The process of the electrons being emitted from heated metallic surfaces is called a. thermionic emission b. electrolysis c. electroplating d. radiofrequency iduction
a. thermionic emission
How many alterations in the direction of the current flow occur in 0.10 second in a 60 Hz AC current? a. 6 b. 12 c. 60 d. 120
b. 12 Remember that one sine wave of 60 Hz takes 1/60 second to complete. That means in 1 second, a 60 Hz AC current produces 60 complete sine waves. That means that in 0.10 seconds (or 1/10 second), 6 complete sine waves are produced. But this question asks how many alternations in the direction though. Each wave has to "changes of direction", so that means that if you have 6 complete sine waves, you get 12 changes of direction.
A semiconductor diode: a. Allows current to flow only from the n type to the p type b. Allows current to flow only from the p type to the n type c. Contains carriers that are also called protons traps d. Contains holes that are also called proton traps e. Is also called an electromechanical device
b. Allows current to flow only from the p type to the n type
A sine wave is designed to graphically display: a. Direct current b. Alternating current c. The inverse of cosine d. More than one, but not all of these
b. Alternating current
As described by the left hand thumb rule, the fingers represent: a. Strength of the electrons b. Direction of the magnetic field c. Direction of the flowing electrons d. Strength of the magnetic field
b. Direction of the magnetic field
An autotransformer works on which law of magnetism? a. Electromagnetic mutual induction b. Electromagnetic self-induction c. Electrification by contract d. Capacitor discharge
b. Electromagnetic self-induction
What does the thumb represent in the left-hand thumb rule? a. Conventional current b. Electron flow c. The direction of the magnetic field d. The direction the conductor moves
b. Electron flow
The p-type semiconductor has: a. One free electron b. Electron holes c. All fixed electrons d. All free electrons
b. Electron holes
What is the primary negative effect of half-wave rectification? a. Unstable electric energy levels. b. Excess heat. c. Both of the above. d. Neither of the above.
b. Excess heat.
The principal purpose of the high-voltage transformer is to do which of the following? a. Adjust voltage b. Increase voltage c. Rectify voltage d. Reduce voltage e. Stabilize voltage
b. Increase voltage
The main function of a step-up transformer is to: a. Increase amperage; decrease voltage b. Increase voltage; decrease amperage c. Decrease amperage; decrease voltage d. Increase voltage; increase amperage
b. Increase voltage; decrease amperage
As the angle between the magnetic lines of flux and the conductor increases, what happens to the induced current? a. It changes direction. b. It decreases c. It increases d. It remains the same
b. It decreases
What is produced from full-wave rectification? a. Pulsating alternating current b. Pulsating direct current c. Steady alternating current d. None of the above
b. Pulsating direct current
To calculate the flow of electrons in a wire passed through a magnetic field, you would use: a. The Left Thumb Rule b. The Left Hand Dynamo Rule c. The Right Hand Motor Rule d. The Right Hand Motor Rule
b. The Left Hand Dynamo Rule Dynamo is another term for generator. With generators, the left hand represents electron flow!
What is the purpose of solid-state rectifiers? a. To prevent the filament from burning out. b. To create direct current. c. To create an alternating current. d. All of the above.
b. To create direct current.
A simple DC generator has essentially the same construction as an AC generator, expect that a DC generator employs the use of a. slip rings b. a commutator c. brushes d. an armature
b. a commutator
An electrical device that is designed to store charges momentarily after charging is a/an a. battery b. capacitor c. thyristor d. dielectric
b. capacitor
You placed a piece of paper of the top of your desk and a wire was sticking through the desktop pointing towards the floor and the ceiling. If current were passing through this wire from the ceiling to the floor, in which direction would the magnetic field around the wire rotate? a. counter clockwise b. clockwise c. North to South d. East to West
b. clockwise This is a tricky question. It's asking about current, so we are using the right hand-thumb rule. However, the current flows up and "out the end" of the thumb, and they are saying the current is the opposite way. Even for the left hand rule, it still flows up, just referring to electron flow. So, turn your hand so that your thumb matches the direction of the current - so you thumb points down, as the current is going. You should notice your fingers are pointing clockwise!
Electrons move downward in a vertical wire. The direction of the associated magnetic field directly around the wire is a. clockwise b. counterclockwise c. in the direction of the electron flow d. opposite to the conventional current
b. counterclockwise This is your basic hand-thumb rule. The *electron* flow is moving downward, which we know is opposite of *current* flow. So, the current flow moves up, and the magnetic field flows the fingers left/counterclockwise.
A magnetic field is produced by a. electric charges at rest b. electric charges in motion c. permanent magnets only d. none of the above
b. electric charges in motion
A motor is a device that converts a. thermal energy into electrical energy b. electrical energy into mechanical energy c. electrical energy into electromagnetic energy d. mechanical energy into electrical energy
b. electrical energy into mechanical energy
Conventional current flows a. from cathode to anode b. from anode to cathode c. only in a solid conductor d. in the same direction as electron flow
b. from anode to cathode
The magnetic flux through a wire loop a. requires a time-varying magnetic field b. is a maximum when the plane of loop is perpendicular to the magnetic field c. increases as the magnetic field decreases d. stays fixed in orientation regardless of electron flow
b. is a maximum when the plane of loop is perpendicular to the magnetic field
Silicon atoms have four electrons in their outer shell that form covalent bonds in a crystal structure. If phosphorus atoms are mixed in, with five electrons in their outer shell, what is created? a. p-type semiconductor b. n-type semiconductor c. Any semiconductor d. None of the above
b. n-type semiconductor
An induced current in a wire loop a. results from a constant magnetic flux b. results from an alternately expanding and contracting field c. is in such a direction that its effects oppose the change producing the current. d. always decreases when the magnetic flux decreases
b. results from an alternately expanding and contracting field
An induced current in a wire loop a. results from a constant magnetic flux. b. results from an alternately expanding and contracting magnetic field. c. is in such a direction that its effects oppose the change producing the current. d. always decreases when the magnetic flux decreases.
b. results from an alternately expanding and contracting magnetic field.
The most efficient x-ray transformer design is the: a. closed-core transformer b. shell-type transformer c. open-core transformer d. air-core transformer
b. shell-type transformer
For a simple AC generator, the value of the induced voltage in the armature loop is maximum when the orientation of the armature as compared to the magnetic field is a. 15 degrees b. 45 degrees c. 90 degrees d. 180 degrees
c. 90 degrees
An autotransformer converts: a. Chemical energy to electrical energy b. Electric energy to chemical energy c. Electric energy to electric energy d. Magnetic energy to electric energy e. Mechanical energy to electrical energy
c. Electric energy to electric energy Transformers don't convert forms of energy, they convert the voltage level.
A semiconductor rectifier: a. Has a heated anode b. Has a heated cathode c. Is a solid state device d. Is an electromechanical device e. Is used only for mammography
c. Is a solid state device
Magnetism may be defined as the ability of a: a. Material to conduct electrical current b. Substance to be attracted by a magnet c. Material to rearrange its magnetic domains d. Material to attract certain other materials
c. Material to rearrange its magnetic domains
If a wire was placed in a magnetic field and current is then sent into the wire, to calculate the movement of the wire within the magnetic field, you would use: a. The Left Thumb Rule b. The Left Hand Dynamo Rule c. The Right Hand Motor Rule d. The Principles of Magnetic Induction
c. The Right Hand Motor Rule I'm not entirely sure about the answer choices given in this question. This actually describes the right hand thumb rule best, but that isn't an option here. With the motor rule, current flow is represented by the left hand. This is supposed to be the answer to this question though. The best way to think about this one is right hand is current flow/left is electron flow and ignore the fact that is says motor.
What happens if the glass of a vacuum-tube rectifier breaks? a. Poisonous gas escapes. b. Radiation escapes. c. The filament burns out. d. All of the above.
c. The filament burns out. There's no gasses in a vacuum tube, and radiation would be able to escape a glass tube anyway.
All of the following are true of induction motors except a. They use multiple phase current and can turn at varying rpm b. Motor power can be regulated by the characteristics of the electromagnets that make up the stator. c. Their design is inherently weak with regard to power d. They are used to spin the x-ray anode disk
c. Their design is inherently weak with regard to power
All of the following are true of transformers except a. They have no moving parts b. They work on the principle of mutual induction c. They work most efficiently on pulsating DC d. They are designed to regulate voltage
c. They work most efficiently on pulsating DC
What is the basic function of a transformer? a. To regulate amperage within a circuit b. To transform DC to AC c. To regulate voltage within a circuit d. To vary resistance within AC circuits
c. To regulate voltage within a circuit
In a generator, the conducting loops across where the magnetic field is induced is called the a. core b. commutator rings c. armature d. slip rings
c. armature
A rectifier a. refers to a type of electromagnetic device b. changes electron flow to current flow c. converts AC to DC d. both b and c
c. converts AC to DC
Compared to the secondary coil of wire in the step-up transformer, the primary coil has a: a. square shape b. smaller diameter c. larger diameter d. rough surface
c. larger diameter The purpose of this is to decrease resistance.
A generator is a device that converts a. electrical energy to thermal energy b. stored energy to electrical energy c. mechanical energy to electrical energy d. electrical energy to mechanical energy
c. mechanical energy to electrical energy
The charge carriers are considered to be negative in a/an a. diode b. triode c. n-type semiconductor d. p-type semiconductor
c. n-type semiconductor
The charge carriers are considered to be a negative in a/an a. diode. b. triode. c. n-type semiconductor. d. p-type semiconductor.
c. n-type semiconductor.
The turns ratio of a transformer is determined by the a. the size of the wire b. type of wire c. number of windings d. size of the laminated plates
c. the number of windings
Which of the following are ways to induce an electromagnetic field? 1. move the conductor 2. move the lines of force 3. vary the magnetic flux a. 1 and 2 b. 2 and 3 c. 1 and 3 d. 1, 2, and 3
d. 1, 2, and 3
Which of the following conditions can occur during electromagnetic induction? 1 magnetic lines of force are cut by a conductor 2. a conductor is cut by magnetic lines of force 3. an emf is induced in the conductor a. 1 only b. 2 only c. 1 and 2 only d. 1, 2, and 3
d. 1, 2, and 3 This is your basic ways to induce current flow with magnetism, just worded funny. Also, remember that emf is "electromotive force", or voltage, which is induced in the conductor as current flows.
Which of the following regulates the amount of induced current in a conductor? 1. Speed at which the wire cuts the magnetic field 2. Strength of the magnetic field 3. Number of batteries in the circuit 4. Angle at which the wire cuts the magnetic field a. 1 and 2 b. 1, 2, 3, and 4 c. 2, 3, and 4 d. 1, 2, and 4
d. 1, 2, and 4
How long does it take for the completion of one sine wave representing 60 Hertz of current? a. 60 seconds b. 6 seconds c. 1/6 second d. 1/60 second
d. 1/60 second
Standard alternating current changes direction in a cycle of: a. Does not change direction. b. Depends on the voltage. c. 30 times a second. d. 60 times a second.
d. 60 times a second.
How many times does AC current change direction in a single minute? a. 30 b. 60 c. 120 d. 7200
d. 7200 You can pretty much figure out any question like this is you know the basic concept that AC current changes directions twice per wave. We are left to assume this problem is referring to 60Hz AC current, that means it changes directions 120 times per second. So, if there are 60 second in one minute, then: 60 sec x 120 = 7,200
What is the disadvantage of vacuum-tube rectifiers compared with solid-state rectifiers? a. Heat produced b. Fragility c. Waste of energy d. All of the above
d. All of the above
What is the reason for using a semiconductor rectifier instead of a vacuum tube? a. It wastes less energy b. It is less delicate c. It avoid low-level radiation d. All of the above
d. All of the above
A semiconductor rectifier is made by putting together n-type and p-type semiconductors. Joined together, what are these semiconductors called? a. Anodes b. Cathodes c. Vacuum tubes d. Diodes
d. Diodes
Once rectified, current may be classified as a. Direct current b. Alternating current c. Electromagnetic direct current d. Pulsating direct current
d. Pulsating direct current
A hysteresis transformer loss can be characterized by which of the following? a. Swirling of currents caused by fleck magnetic fields b. The resistive force of the copper wire within a magnet c. The true resistance of the direct current d. The rapidly changing magnetic domain due to alternating current
d. The rapidly changing magnetic domain due to alternating current
All of the following are true of autotransformers except a. They are considered a variable transformer b. The primary and secondary coils are in series c. The primary and secondary windings share a common coil d. They are effective in controlling voltage on the high voltage side of the circuit
d. They are effective in controlling voltage on the high voltage side of the circuit
A continuous expanding and contracting magnetic field is produced by a. a stationary magnet b. a steady current flowing in a wire c. a battery d. alternating current
d. alternating current
A continuous, expanding and contracting magnetic field is produced by a. a stationary magnet. b. a steady current flowing in a wire. c. a battery. d. alternating current.
d. alternating current. Creation of magnetic field requires *movement* of the magnet, or variation in the current flowing in the wire. Batteries, of course, do not produce magnetic fields. But alternating current varies the current as it switches direction, and therefore produces an expanding and contracting magnetic field.
The magnitude felt by a moving charge through a magnetic field would be least if it were: a. moving directly into the magnetic field b. moving directly away from the magnetic field c. moving at a right angle to the magnetic field d. both a and b
d. both a and b
The magnitude of force felt by a moving charge through a magnetic field would be least if the charge were a. moving directly into the magnetic field b. moving directly away from the magnetic field c. moving at a right angle to the magnetic field d. both a and b
d. both a and b
When using alternating current a. resistance is calculated as impendence (Z) b. electrical production can be graphically expressed as a sinusoidal wave c. it must be rectified prior to the high voltage transformer d. both a and b
d. both a and b
When using alternating current, a. resistance is calculated as impedance (Z). b. electrical production can be graphically expressed as a sinusoidal wave. c. it must be rectified prior to the high voltage transformer. d. both a and b.
d. both a and b. Remember that impedence is another term for resistance, and AC is mapped by sine waves. It should *not* be rectified before going into the transformer, because transformers must operate on AC!
A diode electron tube such as a valve tube a. is used for amplification b. is used to hold electrical charge c. is used to vary the primary voltage d. can be used for rectification
d. can be used for rectification
A diode electron tube: a. is used for amplification b. has a negatively charged anode c. cannot reach saturation d. can be used for rectification
d. can be used for rectification
Losses of energy that occur in the X-ray transformer can be reduced by using a: a. soft iron core b. tungsten steel core c. tungsten-rhenium core d. laminated silicon steel core
d. laminated silicon steel core
The efficiency of a transformer is not affected by: a. eddy current loss b. power loss c. hysteresis loss d. no correct choice
d. no correct choice
An alternately expanding and contracting magnetic field is produced by: a. a stationary magnet b. a steady current flowing in a wire c. a battery d. none of the above
d. none of the above
An electronic device that allows current electricity to flow in one direction only is called a: a. transformer b. filament c. circuit d. rectifier
d. rectifier
The efficiency of a transformer is not affected by a. eddy current loss b. power loss c. hysteresis loss d. the transformer turns ratio
d. the transformer turns ratio Remember that transformer efficiency deals with power loss, and how "efficiently" the transformer can conserve power and avoid loss. The transformer turns ratio affects the output voltage, but not any of the types of power loss seen in transformers.
A bar magnet and a wire loop move with the same linear velocity and direction. The voltage induced in the wire is a. maximum when the wire and magnetic flux are parallel b. directly proportional to their velocities c. inversely proportional to their velocities d. zero
d. zero Remember that induction occurs by motion, either the lines of force (which the magnet is the source of) or the conductor (the wire loop). Since both are moving, there is no motion between them created, so therefore no voltage or current flow is induced.
