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 electrons are negatively charged particles and a positive pole has a deficiency or lack of electrons compared to the negative pole.
2.
An EMF of one volt:
Correct Answer
C. Can sometimes produce a large current.
Explanation
An EMF of one volt can sometimes produce a large current because the amount of current flowing through a circuit is determined by the resistance in the circuit. If the resistance is low, a higher current can flow even with a lower EMF. Therefore, even though one volt may not typically drive much current through a circuit, it can still produce a large current if the resistance is 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 typically measured in amperes (A). A current of 0.1 A (ampere) is considered potentially lethal because it is a high enough current to cause severe harm or even death to a person. Currents in the milliampere (mA) range are generally not lethal, while currents in the order of amperes (A) can be extremely dangerous. Therefore, the correct answer is 0.1 A.
4.
A current of 25 A is most likely drawn by:
Correct Answer
B. A typical household.
Explanation
A current of 25 A is most likely drawn by a typical household because household appliances such as refrigerators, air conditioners, and washing machines require a significant amount of current to operate. A flashlight bulb, clock radio, and power plant typically draw much less current compared to a typical household.
5.
A piece of wire has a conductance of 20 siemens. Its resistance is:
Correct Answer
C. 0.05 Î©.
Explanation
The conductance of a wire is the reciprocal of its resistance. In this case, the wire has a conductance of 20 siemens. Since conductance is the reciprocal of resistance, the resistance of the wire can be calculated by taking the reciprocal of the conductance. Therefore, the resistance of the wire is 1/20 siemens, which simplifies to 0.05 Î©.
6.
A resistor has a value of 300 ohms. Its conductance is:
Correct Answer
A. 3.33 millisiemens.
Explanation
The conductance of a resistor is the reciprocal of its resistance. In this case, the resistance of the resistor is 300 ohms. To find the conductance, we take the reciprocal of the resistance: 1/300 = 0.00333 siemens. Since the answer choices are given in millisiemens and microsiemens, we convert 0.00333 siemens to millisiemens by multiplying by 1000: 0.00333 * 1000 = 3.33 millisiemens. Therefore, the correct answer is 3.33 millisiemens.
7.
A mile of wire has a conductance of 0.6 siemens. Then three miles of the same wire has a conductance of:
Correct Answer
C. 0.2 siemens.
Explanation
The conductance of a wire is inversely proportional to its length. Therefore, if a mile of wire has a conductance of 0.6 siemens, three miles of the same wire would have a conductance of 0.6 siemens divided by 3, which is equal to 0.2 siemens.
8.
A 2-kW generator will deliver approximately how much current, reliably, at 117 V?
Correct Answer
C. 17 A.
Explanation
A 2-kW generator can deliver a maximum power of 2,000 watts. To determine the current, we can use the formula P = IV, where P is power, I is current, and V is voltage. Rearranging the formula to solve for I, we get I = P/V. Plugging in the values, we have I = 2,000/117. This gives us approximately 17 amperes (A) of current. Therefore, the correct answer is 17 A.
9.
A circuit breaker is rated for 15 A at 117 V. This represents approximately how many kilowatts?
Correct Answer
A. 1.76
Explanation
The correct answer is 1.76. To calculate the power in kilowatts, we use the formula P = IV, where P is power in watts, I is current in amperes, and V is voltage in volts. In this case, the current is 15 A and the voltage is 117 V. Plugging these values into the formula, we get P = 15 A * 117 V = 1755 W. To convert watts to kilowatts, we divide by 1000, so the power in kilowatts is 1.755 kW, which can be rounded to 1.76.
10.
You are told that a certain air conditioner is rated at 500 Btu. What is this in kWh?
Correct Answer
D. 0.147
Explanation
The air conditioner is rated at 500 Btu. To convert Btu to kWh, we need to divide the Btu value by 3412.14 (the conversion factor). Therefore, 500 Btu divided by 3412.14 equals 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 measures the amount of energy consumed or produced by an electrical device over a period of time. It is widely used by utility companies to measure and bill for electricity usage. The kilowatt hour is a practical unit as it combines both power (kilowatt) and time (hour) into a single measurement, making it easier to quantify and compare energy consumption.
12.
The frequency of common household ac in the U.S. is:
Correct Answer
A. 60 Hz
Explanation
The frequency of common household AC in the U.S. is 60 Hz. This means that the alternating current changes direction 60 times per second. In the U.S., the standard frequency for residential electricity is 60 Hz, while in some other countries it may be 50 Hz. The frequency of the AC power supply is important because it determines the speed at which electric motors and other electrical devices operate.
13.
Half-wave rectification means that:
Correct Answer
B. Half of the ac wave is chopped off
Explanation
Half-wave rectification refers to the process of converting an alternating current (ac) waveform into a unidirectional current by allowing only one half of the ac waveform to pass through while blocking the other half. In this case, the correct answer states that half of the ac wave is chopped off, indicating that only one half of the waveform is allowed to pass through while the other half is eliminated. This process is commonly achieved using a diode, which acts as a one-way valve for the current.
14.
In the output of a half-wave rectifier:
Correct Answer
B. The effective value is less than that of the original ac wave
Explanation
In a half-wave rectifier, only one half of the input AC wave is allowed to pass through, while the other half is blocked. This means that the output waveform will only have positive half-cycles. Since the negative half-cycles are eliminated, the effective value of the output waveform will be less than that of the original AC wave, which includes both positive and negative half-cycles. Therefore, the effective value is less than that of the original AC wave.
15.
In the output of a full-wave rectifier:
Correct Answer
C. The effective value is the same as that of the original ac wave
Explanation
In a full-wave rectifier, both the positive and negative halves of the AC wave are utilized, resulting in a rectified waveform that closely resembles the original AC waveform. This means that the effective value of the rectified waveform is the same as that of the original AC waveform.
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 to be less hazardous than higher voltages, it can still pose a risk depending on the circumstances. Factors such as the amount of current, duration of exposure, and the specific conditions of the situation can determine the level of danger. For example, if the low voltage is applied to sensitive body parts or if there is a risk of electric shock due to wet or conductive environments, it can be potentially dangerous.
17.
Which of these can represent magnetomotive force?
Correct Answer
B. The ampere-turn
Explanation
Magnetomotive force is a measure of the magnetic field strength produced by an electric current. It is represented by the product of the current (in amperes) and the number of turns in a coil (ampere-turns). The volt-turn is not a valid unit for magnetomotive force. The gauss is a unit of magnetic flux density, not magnetomotive force. The gauss-turn is not a recognized unit in the context of magnetomotive force.
18.
Which of the following units can represent magnetic flux density?
Correct Answer
C. The gauss
Explanation
The gauss is a unit that represents magnetic flux density. It is named after the German mathematician and physicist Carl Friedrich Gauss. The gauss is defined as one maxwell per square centimeter. It is commonly used in the field of magnetism to measure the strength of a magnetic field.
19.
A ferromagnetic material:
Correct Answer
A. Concentrates magnetic flux lines within itself
Explanation
A ferromagnetic material concentrates magnetic flux lines within itself due to its unique atomic structure. This material has aligned magnetic domains that allow it to retain a strong magnetic field even after an external magnetic field is removed. As a result, the magnetic flux lines tend to stay within the material, making it an excellent conductor of magnetic flux. This property is utilized in various applications such as magnetic cores in transformers and magnetic storage devices.
20.
A coil has 500 turns and carries 75 mA of current. The magnetomotive force will be:
Correct Answer
C. 37.5 At
Explanation
The magnetomotive force is determined by multiplying the number of turns in the coil by the current passing 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 * 75 mA = 37,500 At.