Ch. 4 Electromagnetism

Question 1

A magnetic field is produced by:

Answer 1

Electric charges in motion

Question 2

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

Answer 2

d. None of the above

Question 3

A diode electron tube such as a valve tube:

Answer 3

Can be used for rectification

Question 4

The magnetic flux through a wire loop:

Answer 4

Is maximum when the plane of the loop is perpendicular to the magnetic field

Question 5

The charge carriers are considered to be a negative in:

Answer 5

An n-type semiconductor

Question 6

Electrons move downward in a vertical wire. The direction of the associated magnetic field directly around the wire is:

Answer 6

Counterclockwise

Question 7

An induced current in a wire loop:

Answer 7

Can result only from an alternately expanding and contracting magnetic ffield

Question 8

The process of electrons being emitted from heated metallic surfaces is called:

Answer 8

Thermionic emission

Question 9

The magnitude of force felt by a moving charge through a magnetic field would be least if the charge were:

Answer 9

• Moving directly into the magnetic field

- Moving directly away from the magnetic field

Question 10

A generator is a device that converts:

Answer 10

Mechanical energy to electrical energy

Question 11

A simple DC generator has essentially the same construction as an AC generator except that a DC generator employs the use of:

Answer 11

A commutator

Question 12

A rectifier:

Answer 12

Converts AC to DC

Question 13

A motor is a device that converts:

Answer 13

Electrical energy into mechanical energy

Question 14

A transformer with more secondary windings than primary windings:

Answer 14

Has a greater secondary voltage

Question 15

The inherent power loss of electrical conduction through solid wire conductors is:

Answer 15

Minimized with higher voltage transmission

Question 16

A bar magnet and a wire loop move with the same linear velocity and direction. What is the voltage induced in the wire?

Answer 16

Zero

Question 17

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:

Answer 17

90 degrees

Question 18

How many times does an AC current change direction in a single minute?

Answer 18

7,200

120 turns per second

Question 19

The efficiency of a transformer is not affected by:

Answer 19

The transformer turns ratio

Question 20

American generators operate at:

Answer 20

60 Hz

Question 21

A stator consists of:

Answer 21

Electromagnets

Question 22

Conventional current flows:

Answer 22

From anode to cathode

Question 23

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

Answer 23

c. They work most efficiently on pulsating DC

Question 24

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:

Answer 24

0.05 amps

Question 25

The turns ratio of a transformer is determined by the:

Answer 25

Number of windings

Question 26

An electrical device that is designed to store charge momentarily after charging is a:

Answer 26

Capacitor

Question 27

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

Answer 27

d. They are effective in controlling voltage on the high voltage side of the circuit

Question 28

The material of choice for semiconductors is:

Answer 28

Silicon

Question 29

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

Answer 29

c. Their design is inherently weak with regard to power

Question 30

When using alternating current,

Answer 30

• Resistance is calculated as impedance (Z)

- Electrical production can be graphically expressed as a sinusoidal wave