Electromag. WS 7-1/2/3

C

The symbol for a transformer is:

A

Which accurately represents the transformer law?

Given a closed loop of wire w/ no electron flow, an electric current can be induced if: a. A changing magnetic field is present. b. A constant magnetic field is present. c. No magnetic field is present. d. The loop is cycled open/close.

a. A changing magnetic field is present

In an electric generator: a. A coil of wire is rotated in a magnetic field. b. A transformer is charged. c. AC is changed to DC. d. Chemical energy is converted to electrical energy.

a. A coil of wire is rotated in a magnetic field.

A transformer operates on/only: a. AC but not on DC. b. both DC and AC. c. DC but not on AC. d. above its critical current.

a. AC but not on DC.

The electric current produced by an AC generator has: a. Alternating positive/negative intensity. b. Constant negative intensity. c. Constant positive intensity. d. Pulsating negative intensity.

a. Alternating positive/negative intensity.

Device designed to measure electron flow in a conductor is known as a/an: a. Ammeter. b. Choke coil. c. Electromagnet. d. Solenoid.

a. Ammeter.

An autotransformer: a. Contains a single coil that serves as both primary/secondary coils. b. Controls x-ray tube current. c. Is a shell type of transformer. d. Is an electromechanical device.

a. Contains a single coil that serves as both primary/secondary coils.

Which would be classified as electromechanical devices? a. Generators and motors b. Generators and rectifiers c. Motors and rectifiers d. Transformers and electromagnets

a. Generators and motors

The turns ratio is defined as: a. Number of secondary windings - primary windings. b. Primary iron core + secondary iron core. c. Primary voltage ÷ secondary voltage. d. Primary windings ÷ number of secondary windings.

a. Number of secondary windings - primary windings.

The main difference between an AC/DC electric generator is: a. The type of commutator ring. b. A magnet. c. A source of EMF. d. A transformer.

a. The type of commutator ring.

The fact that an electric current is induced if the conductor is in a changing magnetic field is/was: a. known as Faraday's law. b. known as Ohm's law. c. the statement of the 2nd law of electro-magnetics. d. discovered by Lenz.

a. known as Faraday's law.

A transformer with a turns ratio of 1000:1 is: a. A step-down transformer. b. A step-up transformer. c. An autotransformer. d. Used to increase current.

b. A step-up transformer.

What is the transformer that looks like a square donut called? a. Auto b. Closed-core c. High-frequency d. Induction

b. Closed-core

When applying the right-hand rule to a straight wire, the thumb indicates the direction of the: a. Circuit resistance. b. Electric current. c. Electric field. d. Electric potential.

b. Electric current.

Which of the scientists is associated w/ early development of electromagnetism? a. Edison b. Faraday c. Marconi d. Planck

b. Faraday

Which is most related to electromechanical devices? a. Edison's law of electromechanics b. Faraday's experiment c. Lenz's 1st law of electromagnetics d. Oersted's experiment on mutual induction

b. Faraday's experiment

The electric generator is most closely associated w/ experiments conducted by: a. Edison. b. Faraday. c. Lenz. d. Oersted.

b. Faraday.

The principal difference between a solenoid and an electromagnet is magnetic field: a. Homogeneity. b. Intensity. c. Penetrability. d. Polarity.

b. Intensity.

A modern dry-cell battery is a source of: a. Coulomb per joule. b. Joule per coulomb. c. Newton per coulomb. d. Ohm per volt.

b. Joule per coulomb.

Difference between self-induction/mutual induction is: a. Mutual induction is the basis for an electric motor/self-induction is the basis for a transformer. b. Mutual induction requires 2 coils and self-induction requires only 1. c. Only self-induction can create EMF.

b. Mutual induction requires 2 coils and self-induction requires only 1.

Electromagnetic induction refers to production of: a. A magnetic field. b. A static charge. c. An electric current. d. An electromagnet.

c. An electric current.

Primary to secondary coupling in a transformer is enhanced by: a. 60 Hz. b. AC. c. An iron core. d. DC.

c. An iron core.

When an AC source is connected to a coil of wire: a. A constant magnetic field is generated. b. A front EMF is produced. c. An opposite EMF is induced. d. Electromagnetic radiation is produced.

c. An opposite EMF is induced.

The voltaic pile: a. Consists of a magnet/conductor. b. Consists of a pile of charges. c. Consists of zinc/copper plates sandwiched together. d. Is a modern dry-cell battery.

c. Consists of zinc/copper plates sandwiched together.

An electromagnet: a. Cannot be turned off. b. Has an air core. c. Is a coil of wire wound around an iron core. d. Produces a magnetic field w/ or without an electric current.

c. Is a coil of wire wound around an iron core.

Electromotive force (EMF): a. Is an electrical mechanical force. b. Is expressed in joules. c. Is expressed in volts. d. Stands for electromagnetic field.

c. Is expressed in volts.

Which statement about transformers is correct? a. If there were equal numbers of primary/secondary coil turns, turn ratio would be 0. b. In shell-type transformers, primary/secondary coils are wound on different cores. c. Laminated transformer cores are more efficient than unlaminated ones.

c. Laminated transformer cores are more efficient than unlaminated ones.

In an induction motor, the only part to rotate is the: a. Cathode. b. Electromagnet. c. Rotor. d. Stator.

c. Rotor.

One law of electromagnetics states that: a. An electric current is induced in a circuit if some part of that circuit is in a magnetic field. b. Electrostatics can be converted to magnetism. c. The induced current flows in the opposite direction of the inducing action. d. The right-hand rule is used to determine direction of the induced current.

c. The induced current flows in the opposite direction of the inducing action.

When a step-up transformer is in use: a. The primary winding has more turns than the secondary winding. b. The secondary current is greater than the primary current. c. The secondary voltage is greater than the primary voltage.

c. The secondary voltage is greater than the primary voltage.

If a transformer produces a large secondary current from a small primary current: a. Power will be increased. b. The turns ratio will be greater than c. The turns ratio will be less than d. voltage will be larger on the secondary side than on the primary side.

c. The turns ratio will be less than (INVERSED)

Which statement about generators/motors is true? a. They are electromagnets. b. They both require commutators. c. They convert energy from 1 form into another. d. They have both primary/secondary windings.

c. They convert energy from 1 form into another.

The principal application of a transformer in an x-ray imaging system is to: a. Change AC to DC b. Change DC to AC. c. Change frequency. d. Change voltage.

d. Change voltage.

In an electric motor: a. A coil of wire is mechanically rotated. b. A commutator ring is not necessary. c. AC is changed to DC. d. Electric current is supplied to a coil of wire.

d. Electric current is supplied to a coil of wire.

When an electric current is induced by mutual induction, such current flows: a. According to Faraday's law. b. According to Lenz's law. c. According to Oersted's law. d. In the secondary coil.

d. In the secondary coil.

When designing a transformer, the change in current is: a. Dependent on the supply voltage. b. Directly proportional to the voltage change. c. In the same direction as the voltage change. d. Inversely proportional to the turns ratio.

d. Inversely proportional to the turns ratio.

The output current in a step-up transformer is: a. Higher than the input current. b. Independent of the input current. c. Independent of the turns ratio. d. Lower than the input current.

d. Lower than the input current. (INVERSED)

Transformers have iron cores to intensify the: a. Electric current. b. Electric potential. c. Electric power. d. Magnetic field.

d. Magnetic field.

If DC is applied to the primary coil of a step-up transformer, what is the result in the secondary coil? a. AC. b. Increased current c. Increased magnetic field d. Nothing

d. Nothing

The experimental link connecting electric/magnetic forces was discovered by: a. Edison. b. Faraday. c. Lenz. d. Oersted.

d. Oersted.

An electron moving in a conductor: a. Causes conductor to behave as a bar magnet. b. Causes conductor to bend. c. Produces a magnetic field in the conductor. d. Produces a magnetic field perp to the conductor.

d. Produces a magnetic field perp to the conductor.

The magnetic field produced by an electromagnet has: a. Alternating poles. b. Neither a north nor a south pole. c. Only a north pole. d. Properties similar to a bar magnet.

d. Properties similar to a bar magnet

Which is based on electromagnetic induction? a. AC current b. Battery c. DC current d. Radio reception

d. Radio reception

An induction motor is used in an x-ray imaging system to: a. Control current. b. Measure mAs. c. Provide rectification. d. Rotate the anode.

d. Rotate the anode.

Which is a transformer design used in x-ray imaging systems? a. Capacitor type b. Filament type c. Rectifier type d. Shell type

d. Shell type

The transformer changes: a. Electric current to voltage. b. Electric energy to electromagnetic energy. c. Electric energy to mechanical energy. d. The amplitude of the voltage.

d. The amplitude of the voltage.

A transformer "transforms" or changes electric: a. Frequency. b. Impedance. c. Power. d. Voltage.

d. Voltage.

The magnetic field produced by/in: a. a solenoid is more intense than that produced by an electromagnet. b. AC is stronger than that produced by DC. c. an AC source is constant. d. a transformer is based on mutual induction.

d. a transformer is based on mutual induction.