Ch. 4 Electromagnetism Flashcards
A magnetic field is produced by:
Electric charges in motion
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
A diode electron tube such as a valve tube:
Can be used for rectification
The magnetic flux through a wire loop:
Is maximum when the plane of the loop is perpendicular to the magnetic field
The charge carriers are considered to be a negative in:
An n-type semiconductor
Electrons move downward in a vertical wire. The direction of the associated magnetic field directly around the wire is:
Counterclockwise
An induced current in a wire loop:
Can result only from an alternately expanding and contracting magnetic ffield
The process of electrons being emitted from heated metallic surfaces is called:
Thermionic emission
The magnitude of force felt by a moving charge through a magnetic field would be least if the charge were:
- Moving directly into the magnetic field
- Moving directly away from the magnetic field
A generator is a device that converts:
Mechanical energy to electrical energy
A simple DC generator has essentially the same construction as an AC generator except that a DC generator employs the use of:
A commutator
A rectifier:
Converts AC to DC
A motor is a device that converts:
Electrical energy into mechanical energy
A transformer with more secondary windings than primary windings:
Has a greater secondary voltage
The inherent power loss of electrical conduction through solid wire conductors is:
Minimized with higher voltage transmission
A bar magnet and a wire loop move with the same linear velocity and direction. What is the voltage induced in the wire?
Zero
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 fields is:
90 degrees
How many times does an AC current change direction in a single minute?
7,200
120 turns per second
The efficiency of a transformer is not affected by:
The transformer turns ratio
American generators operate at:
60 Hz
A stator consists of:
Electromagnets
Conventional current flows:
From anode to cathode
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
If a transformer is supplied with 16 volts and 4 amperes, the output current from this transformer with an output voltage of 1200 volts would be:
0.05 amps
The turns ratio of a transformer is determined by the:
Number of windings
An electrical device that is designed to store charge momentarily after charging is a:
Capacitor
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
The material of choice for semiconductors is:
Silicon
All of the following are true of induction motors EXCEPT:
a. They use multiphase 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 tube anode disk
c. Their design is inherently weak with regard to power
When using alternating current,
- Resistance is calculated as impedance (Z)
- Electrical production can be graphically expressed as a sinusoidal wave
