CHAPTER 2 - ELECTRICAL UNITS GIBILISCO 7TH EDITION

In an electric dipole of constant polarity, the positive charge center (a) has more electrons than the negative charge center. (b) has the same number of electrons as the negative charge center. (c) has fewer electrons than the negative charge center. (d) sometimes has more electrons than the negative charge center, sometimes has the same number, and sometimes has fewer.

c

If you touch two points that have DC voltage between them, one point with your left hand and the other point with your right hand, which of the following voltages would present the greatest electrocution hazard? (a) 1.5 V (b) 15 V (c) 150 V (d) All three voltages would present equal electrocution hazards because it's the current that kills, not the voltage.

c

If you increase the DC voltage across a resistor by a factor of 100 but you also increase the resistance to keep the current constant, then (assuming the resistor doesn't burn out) the resistor will (a) 100 times as much power as it did before. (b) 10 times as much power as it did before. (c) the same amount of power as it did before. (d) 1/10 as much power as it did before.

a

If a length of wire exhibits 500 mS of conductance, then it has a resistance of (a) 0.02 Ω. (b) 0.2 Ω. (c) 2 Ω. (d) an amount that depends on how much current the wire carries.

c

A 330-Ω resistor has a conductance of (a) 0.303 mS. (b) 3.03 mS. (c) 30.3 mS. (d) 303 mS.

b

A circuit breaker is rated for 15.0 A in a 13.8-V DC automotive system (with the alternator running). This breaker should cut off the current if you connect a set of devices that demand a total of more than (a) 207 W. (b) 20.7 W. (c) 1.09 W. (d) 920 mW.

a

A heater warms a space by 1,000,000 J over a period of time. This amount of energy represents (a) 1055 Btu. (b) 948 Btu. (c) 10.55 Btu. (d) None of the above. The British thermal unit quantifies power, not energy!

b

Suppose that a 6.00-V battery delivers 4.00 W of power to a light bulb. How much current flows through the bulb? (a) 24.0 A (b) 1.50 A (c) 667 mA (d) We must know the bulb's resistance to calculate the current.

c

Imagine that a span of wire 200 m long has a conductance of 900 mS. A 600-m length of this wire would have a conductance of (a) 8.10 S. (b) 2.70 S. (c) 300 mS. (d) 100 mS.

c

Which of the following units quantifies energy? (a) The erg (b) The kilowatt-hour (c) The joule (d) All of the above

d

Suppose that an AC cycle repeats at a constant rate of one full cycle every 0.02 second. This wave has a frequency of (a) 500 Hz. (b) 200 Hz. (c) 50 Hz. (d) 20 Hz.

c

In many countries outside the United States, utility AC electricity has a frequency of (a) 33 Hz. (b) 50 Hz. (c) 75 Hz. (d) 100 Hz.

b

If we could see them, the magnetic flux contours near a straight, current-carrying wire would look like (a) concentric circles with the wire at their centers. (b) straight lines parallel to the wire. (c) straight lines that all pass through the wire at right angles. (d) spirals that originate on the wire and all lie in planes perpendicular to the wire.

a

A high DC voltage across a load (a component with DC resistance) (a) gives rise to poor conductance. (b) can exist even if the load has low resistance. (c) invariably drives a lot of current through the load. (d) All of the above

b

Suppose that DC flows through a wire coil. The magnetomotive force produced by this coil depends on (a) the number of turns in the coil. (b) the diameter of the coil. (c) the resistance of the coil. (d) the material around which the coil is wound.

a

Suppose that 3 A of current flows through a 100-turn, circular loop of wire wound around a powdered-iron rod. Then we remove the rod, leaving the coil with an air core. The magnetomotive force (a) decreases. (b) increases. (c) stays the same. (d) drops to zero.

c

Which, if any, of the following units can express magnetomotive force? (a) The ampere-turn per square meter (b) The weber per square meter (c) The maxwell per square meter (d) None of the above

d

Given a sine-wave AC input, the output of a full-wave rectifier (a) has an average voltage equal to the peak voltage. (b) comprises constant DC just like a battery produces. (c) is pulsating DC. (d) is also a sine wave.

c

Given a sine-wave AC input, the output of a half-wave rectifier (a) has an average voltage equal to the peak voltage. (b) comprises constant DC just like a battery produces. (c) is pulsating DC. (d) is also a sine wave.

c

Which of the following units can express overall magnetic-field quantity? (a) The weber (b) The coulomb (c) The volt (d) The watt

a