問題一覧
1
Only if a force on a particle is conservative:
is its work zero when the particle moves exactly once around any closed path
2
A nonconservative force:
none of the above
3
The sum of the kinetic and potential energies of a system of objects is conserved:
none of the above
4
A force on a particle is conservative if:
its work depends on the end points of every motion, not on the path between
5
Two particles interact by conservative forces. In addition, an external force acts on each particle. They complete round trips, ending at the points where they started. Which of the following must have the same values at the beginning and end of this trip?
the potential energy of the two-particle system
6
Two objects interact with each other and with no other objects. Initially object A has a speed of 5 m/s and object B has a speed of 10 m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4 m/s and B has a speed of 7 m/s. We can conclude:
mechanical energy was decreased by nonconservative forces
7
A good example of kinetic energy is provided by:
a tornado
8
No kinetic energy is possessed by:
an elevator standing at the fifth floor
9
The wound spring of a clock possesses:
potential but no kinetic energy
10
A body at rest in a system is capable of doing work if:
it is free to move in such a way as to decrease the potential energy of the system
11
A golf ball is struck by a golf club and falls on a green three meters above the tee. The potential energy of the Earth-ball system is greatest:
when the ball reaches the highest point in its flight
12
Given a potential energy function U(x), the corresponding force F is in the positive x direction if:
U is a decreasing function of x
13
The thermal energy of a system consisting of a thrown ball, Earth, and the air is most closely associated with:
motions of individual particles within the ball and the air
14
The center of mass of a uniform disk of radius R is located:
at the center
15
The charge on a glass rod that has been rubbed with silk is called positive:
by arbitrary convention
16
To make an uncharged object have a negative charge we must:
add some electrons
17
To make an uncharged object have a positive charge:
remove some electrons
18
When a hard rubber rod is given a negative charge by rubbing it with wool:
negative charges are transferred from wool to rod
19
An electrical insulator is a material:
through which electrons do not flow easily
20
When the frequency of the oscillator in a series RLC circuit is doubled:
the capacitive reactance is halved
21
In an RLC series circuit, the source voltage is leading the current at a given frequency f. If f is lowered slightly, then the circuit impedance
decrease
22
An RIC series circuit, connected to a source E, is at resonance. Then:
the voltage across R equals the applied voltage
23
The core of a transformer is made in a laminated form to:
prevent eddy currents
24
Gauss' law for magnetism tells us:
that magnetic monopoles do not exist
25
The statement that magnetic field lines form closed loops is a direct consequence of:
Gauss' law for magnetism
26
According to Gauss' law for magnetism, magnetic field lines:
form closed loops
27
The magnetic field lines due to an ordinary bar magnet:
form closed curves
28
Two of Maxwell's equations contain a path integral on the left side and an area integral on the right. For them:
the path must lie in the area, away from its boundary
29
The common dry cell gives a voltage of about
1.5 V
30
Operating stick for disconnect switches is made of
wood
31
The filament of incandescent lamp is made of
tungsten
32
Maximum efficiency of halfwave rectifier
40.5 %
33
Maximum of fullwave rectifier
80.2 %
34
An alternating current with a frequency of 60 Hz is passed through a moving coil galvanometer that measures DC current. What will the galvanometer reading be equal to? (A) the peak value of the AC current (B) the average value of the AC current (C) the rms value (D) a negligible amount
D
35
Which of the following effects are generally less for an alternating current than for a direct current?
chemical effects
36
Which of the following statements regarding transformers is FALSE? (A) The copper losses (I?R) in the primary and secondary coils are equal. (B) Transformer power losses are generally low, approximately 1-3%. (C) Power losses in transformers are converted to heat, which is then dissipated. (D) One three-phase transformer weighs more than three equivalent single- phase transformers.
D
37
Which of the following statements about induction motors is FALSE? (A) They are used to increase the line power factor. (B) They have no slip rings, no brushes, and no excited field current. (C) They have no commutators and no windings on the armature. (D) Squirrel-cage induction motors operate at essentially constant speeds.
A
38
A single-phase induction motor is not self-starting. Instead, auxiliary methods must be used, such as varying inductance, resistance, and capacitance. Which of the following is FALSE regarding this situation? (A) A capacitor motor uses capacitance to split the phase, resulting in two phases almost 90° apart. (B) Capacitor motors have lower starting torque than comparably sized single phase induction motors. (C) To obtain a higher reactance, a capacitor can be used when starting and then be switched out of the circuit by mechanical means. (D) If the capacitor remains in the circuit, the power factor will have a value close to unity.
B
39
A squirrel-cage motor has such low resistance that it draws excessive currents when starting. Which of the following actions will NOT reduce this problem?
using a class A motor
40
Which of the following statements about AC generators is FALSE? (A) The poles of an AC generator are located on the rotor. (B) The three main types of AC generator are direct-connect engine driven, water driven, and turbine driven. (C) An AC generator uses commutators. (D) Large turbine driven generators usually have two pole rotors to accommo date the high speed of the turbine.
C
41
Which of the following is FALSE regarding rotating machinery? (A) The avoidance of harmonics in the production of a sine wave can be achieved by using a coil having multiple loops passing through adjacent slots rather than using only one pair of slots. (B) Uniformity in the production of flux on a pole can be obtained by using distributed field windings over a portion of the rotor surface. (C) AC generator ratings are usually given in units of kVA (kilovolt amps). (D) At zero power factor, the generator delivers real power to a load.
D
42
A conduit band needed if the conduit end is running through an outlet box for connection of lightning fixture, convenience outlet, etc.
Offset bend
43
It is known also as cold standby reserve
back-up reserve
44
According to the Philippine Electrical Code at an ambient temperature of 30°C, 8.0 mm2 copper conductors with the following insulation have the following ampacities: TW insulation - 30 A; THW insulation - 45 A; for THEN insulation - 50 A. if each of these insulated wires carries the same amperes which will generate heat the fastest?
TW insulated wire
45
In a synchronous motor, the motor copper losses are met by
dc source
46
The terminal for size 50 sq. mm cooper conductor without any markings to indicate the temperature rating of the terminal is assumed to have a minimum terminal temperature rating of:
60 C
47
The efficiency of thermal power plant is approximately
0.3
48
Grid and Distribution System Installation and maintenance are governed by which of the following?
NEA
49
What is the allowable voltage drop for distribution system?
0.03