1.
A positive electric pole
Correct Answer
B. Has fewer electrons than the negative pole
Explanation
A positive electric pole has fewer electrons than the negative pole because in an electric circuit, electrons flow from the negative terminal (which has an excess of electrons) to the positive terminal (which has a deficiency of electrons). This movement of electrons creates an electric current.
2.
An EMF of 1 V
Correct Answer
C. Can sometimes produce a large current
Explanation
An EMF of 1 V can sometimes produce a large current because the amount of current flowing through a circuit depends on the resistance in the circuit. If the resistance is low, even a small EMF can drive a large current. Therefore, it is possible for a 1 V EMF to produce a large current if the resistance in the circuit is sufficiently low.
3.
A potentially lethal electric current is on the order of
Correct Answer
D. 0.1 A
Explanation
A potentially lethal electric current is on the order of 0.1 A. This is because electric currents above this level can cause severe harm or even death to a person. It is important to note that the human body has a certain threshold for electric current, and anything above 0.1 A can disrupt the normal functioning of the body's electrical systems, leading to serious consequences. Therefore, it is crucial to handle electricity with caution and ensure safety measures are in place to prevent exposure to currents above this level.
4.
A current of 25 A is most likely drawn by
Correct Answer
B. A typical household
Explanation
A typical household is most likely to draw a current of 25 A because it includes various electrical appliances and devices such as refrigerators, air conditioners, washing machines, and others that require a significant amount of power to operate. These appliances collectively draw a substantial amount of current, resulting in a current of 25 A.
5.
A piece of wire has a conductance of 20 S. Its resistance is
Correct Answer
C. 0.05 â„¦
Explanation
The resistance of a wire is the reciprocal of its conductance. Therefore, if the wire has a conductance of 20 S, its resistance would be 1/20, which is equal to 0.05 â„¦.
6.
A resistor has a value of 300 â„¦. Its conductance is
Correct Answer
A. 3.33 mS
Explanation
The conductance of a resistor can be calculated using the formula G = 1/R, where R is the resistance. In this case, the resistance is given as 300 â„¦, so the conductance would be 1/300 â„¦, which is equal to 0.00333 S. Since the options are given in different units, we need to convert this value to the appropriate unit. 0.00333 S is equivalent to 3.33 mS (millisiemens). Therefore, the correct answer is 3.33 mS.
7.
A span of wire 1 km long has a conductance of 0.6 S. What is the conductance of a span ofthis same wire that is 3 km long?
Correct Answer
C. 0.2 S
Explanation
The conductance of a wire is inversely proportional to its length. In this case, the wire is 3 times longer than the original wire, so its conductance will be 1/3 of the original conductance. Therefore, the conductance of a 3 km long wire will be 0.2 S.
8.
Approximately how much current can a 2-kW generator reliably deliver at 117 V?
Correct Answer
C. 17 A
Explanation
A 2-kW generator can reliably deliver a maximum power of 2000 watts. To calculate the current, we can use the formula: power (in watts) = voltage (in volts) Ã— current (in amperes). Rearranging the formula, we get current = power / voltage. Plugging in the values, we get current = 2000 watts / 117 volts = approximately 17 amperes. Therefore, the correct answer is 17 A.
9.
A circuit breaker is rated for 15 A at 117 V. Approximately how much power does this represent?
Correct Answer
A. 1.76 kW
Explanation
The power can be calculated using the formula P = IV, where P is power, I is current, and V is voltage. Given that the circuit breaker is rated for 15 A at 117 V, the power can be calculated as 15 A * 117 V = 1755 W. Converting this to kilowatts, we get 1.755 kW, which can be rounded to 1.76 kW.
10.
You are told that an air conditioner has cooled a room by 500 Btu over a certain period oftime. What is this amount of energy in kWh?
Correct Answer
D. 0.147 kWh
Explanation
The correct answer is 0.147 kWh. Btu (British thermal unit) is a unit of energy, while kWh (kilowatt-hour) is a unit of electrical energy. To convert Btu to kWh, we need to divide the amount of energy in Btu by the conversion factor of 3412.14. In this case, dividing 500 Btu by 3412.14 gives us approximately 0.147 kWh.
11.
Of the following energy units, the one most often used to define electrical energy is
Correct Answer
D. The kilowatt-hour
Explanation
The kilowatt-hour is the most commonly used unit to define electrical energy. It is a unit of energy equal to the amount of energy consumed by a 1-kilowatt appliance operating for one hour. This unit is widely used in measuring electricity consumption in homes, businesses, and industries. It provides a practical and convenient way to quantify and bill for electrical energy usage. The other units listed, such as Btu, erg, and foot-pound, are more commonly used in other fields of energy measurement and not specifically for electrical energy.
12.
The frequency of common household ac in the United States is
Correct Answer
A. 60 Hz
Explanation
The correct answer is 60 Hz because in the United States, the standard frequency for common household AC (alternating current) is 60 Hz. This means that the direction of the current changes 60 times per second. This frequency is important for the proper functioning of electrical appliances and devices in the United States.
13.
Half-wave rectification means that
Correct Answer
B. Half of the ac wave is cut off.
Explanation
Half-wave rectification is a process in which only one half of the alternating current (ac) wave is allowed to pass through, while the other half is cut off. This is typically achieved by using a diode, which allows current to flow in only one direction. As a result, the negative half of the ac wave is blocked, while the positive half is allowed to pass through. This process effectively converts the ac wave into a pulsating direct current (dc) waveform.
14.
In the output of a half-wave rectifier,
Correct Answer
B. The effective voltage is less than that of the ac input wave
Explanation
In a half-wave rectifier, only one half of the AC input wave is converted into a DC output wave. This means that during the positive half-cycle of the AC input wave, the rectifier allows the current to flow, while during the negative half-cycle, the rectifier blocks the current. As a result, the effective voltage of the output wave is less than that of the AC input wave because it is only utilizing half of the input wave.
15.
In the output of a full-wave rectifier,
Correct Answer
C. The effective voltage is the same as that of the ac input wave.
Explanation
In a full-wave rectifier, both the positive and negative halves of the AC input wave are converted into positive DC output. This is achieved by using a bridge circuit or a center-tapped transformer. As a result, the effective voltage of the output waveform is the same as that of the AC input wave. The rectifier ensures that the negative half of the input wave is flipped to become positive, resulting in a continuous positive waveform with the same effective voltage.
16.
A low voltage, such as 12 V,
Correct Answer
D. Can be dangerous under certain conditions
Explanation
A low voltage, such as 12 V, can be dangerous under certain conditions. While low voltage is generally considered safer than high voltage, it can still pose a risk depending on the circumstances. For example, if the low voltage is being applied directly to the body, it can cause electric shock and injury. Additionally, if the low voltage is being used in certain industrial or electrical systems, it can still cause harm if not handled properly or if there are faults in the system. Therefore, it is important to exercise caution and follow safety guidelines when dealing with any voltage, including low voltage.
17.
Which of the following units can represent magnetomotive force?
Correct Answer
B. The ampere-turn
Explanation
The magnetomotive force is a measure of the force that produces magnetic flux in a magnetic circuit. It is represented by the product of the current (in amperes) flowing through a coil and the number of turns in the coil. Therefore, the unit that can represent magnetomotive force is the ampere-turn, which combines the unit of current (amperes) with the unit of turns.
18.
Which of the following units can represent magnetic flux density?
Correct Answer
C. The gauss
Explanation
The gauss is a unit that can represent magnetic flux density. It is named after the German mathematician and physicist Carl Friedrich Gauss. Magnetic flux density, also known as magnetic induction or magnetic field strength, is a measure of the strength of a magnetic field in a given area. The gauss is commonly used in scientific and engineering applications to quantify magnetic fields.
19.
A ferromagnetic material
Correct Answer
A. Concentrates magnetic flux lines within itself
Explanation
A ferromagnetic material concentrates magnetic flux lines within itself. This means that when a ferromagnetic material is placed in a magnetic field, it attracts and absorbs the magnetic field lines, causing them to be more concentrated within the material. This is due to the alignment of the magnetic domains within the material, which enhances its magnetic properties. As a result, the magnetic flux lines are confined within the ferromagnetic material, leading to a stronger magnetic effect compared to other materials.
20.
A coil has 500 turns and carries 75 mA of current. The magnetomotive force is
Correct Answer
C. 37.5 At
Explanation
The magnetomotive force in a coil is given by the product of the number of turns and the current flowing through it. In this case, the coil has 500 turns and carries 75 mA of current. Therefore, the magnetomotive force is calculated as 500 turns multiplied by 75 mA, which equals 37.5 At.