Magnetism and Electromagnetism

Q1: Which electromagnetic device uses brushes and a commutator?

A A speaker

B A dc generator

C A relay

D A solenoid

Q2: Which two values are plotted on a B-H curve graph?

A Reluctance and flux density

B Permeability and reluctance

C Magnetizing force and permeability

D Flux density and magnetizing force

Q3: The component that produces power in an electromagnetic generator is called the

A armature

B field winding

C commutator

D brush

Q4: The Hall effect

A is a phenomenon with no practical applications

B is used in various sensor applications

C can develop potentials of thousands of volts

D is the basis for solar cell operation

Q5: Permeability is the inverse equivalent of which electrical term?

A Voltage

B Current

C Resistance

D Conductance

Q6: A Hall effect sensor

A exists only in theory

B is a noncontacting magnetic sensor

C can operate only a few times before failure

D produces very large voltages

Q7: What is the flux density of a magnetic field whose flux is 3000 µWb and cross-sectional area is 0.25 m2?

A
12,000 mu.gifT

B
83,330 T

C
0 T

D
More information is needed in order to find flux density.

Q8: Which electromagnetic device has a flexible cone?

A A speaker

B A dc generator

C A relay

D A solenoid

Q9: The polarity of induced voltage while a field is collapsing is

A independent of the force creating the field

B opposite to the force creating the field

C identical to the force creating the field

D present only if the force is stationary

Q10: The Hall effect

A is a phenomenon with no practical applications

B is used in various sensor applications

C can develop potentials of thousands of volts

D is the basis for solar cell operation

Q11: The unit of flux density is known as

A magnetomotive force

B a weber

C a maxwell

D a tesla

Q12: What is the reluctance of a material that has a length of 0.045 m, a cross-sectional area of 0.015 m2, and a permeability of 2500 µWb/At·m?

A
833.33 µAt/Wb

B
0.27 At/Wb

C
1200 At/Wb

D
More information is needed in order to find the reluctance.

Q13: Which electromagnetic device contains an armature?

A A speaker

B A dc generator

C A relay

D A solenoid

Q14: What is the reluctance of a material that has a length of 0.045 m, a cross-sectional area of 0.015 m2, and a permeability of 2500 µWb/At·m?

A
833.33 µAt/Wb

B
0.27 At/Wb

C
1200 At/Wb

D
More information is needed in order to find the reluctance.

Q15: "Series" and "parallel" as applied to dc motors refer to

A the connection of the motor and controller

B the connection of the field coil and armature windings

C the connection of the brush and commutator

D the connection of the motor batteries

Q16: What are the effects of moving a closed wire loop through a magnetic field?

A A voltage is induced in the wire.

B A current is induced in the wire.

C The polarity across the wire depends on the direction of motion.

D All of the above

Q17: What is the magnetomotive force in a 150-turn coil of wire with 2 A flowing through it?

A
13.33 mAt

B
300 At

C
75 At

D
152 At

Q18: A Hall effect sensor

A exists only in theory

B is a noncontacting magnetic sensor

C can operate only a few times before failure

D produces very large voltages

Q19:
16.Which electromagnetic device has a movable iron core called a plunger?

A A speaker

B A dc generator

C A relay

D A solenoid

Q20: What do you call the characteristic of a magnetic material whereby a change in magnetization lags the application of a magnetizing force?

A Hysteresis

B Induction

C Retentivity

D Reluctance

Q21: How much flux is there in a magnetic field when its flux density is 5000 mu.gifT and its cross-sectional area is 300 mm2?

A
16.67 mWb

B
5.0 mu.gifWb

C
3.0 mWb

D
1.5 mu.gifWb


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