1.
Biasing in an amplifier circuit:
Correct Answer
C. Can be done using voltage dividers
Explanation
Biasing in an amplifier circuit refers to the process of setting the DC operating point of the amplifier to ensure proper amplification of the input signal. This is typically achieved using voltage dividers, which provide a stable and constant bias voltage to the amplifier. By setting the bias voltage correctly, the amplifier operates in its linear region, preventing distortion and ensuring accurate amplification. Therefore, biasing using voltage dividers is an essential technique to maintain the stability and performance of an amplifier circuit.
2.
A transistor can be protected from needless overheating by:
Correct Answer
A. Current-limiting resistors
Explanation
Current-limiting resistors can protect a transistor from overheating by limiting the amount of current flowing through the transistor. Transistors have a maximum current rating, and exceeding this limit can cause overheating and damage. By using current-limiting resistors, the amount of current flowing through the transistor can be controlled and kept within safe limits, preventing overheating.
3.
Bleeder resistors:
Correct Answer
A. Are connected across the capacitor in a power supply
Explanation
Bleeder resistors are connected across the capacitor in a power supply to discharge the capacitor when the power supply is turned off. This is done to ensure the safety of the user and prevent any residual charge from remaining in the capacitor, which could potentially cause electric shock or damage to the circuitry. By providing a discharge path for the capacitor, bleeder resistors help in dissipating the stored energy and ensuring a safe power-down state for the power supply.
4.
Carbon-composition resistors:
Correct Answer
C. Are comparatively nonreactive
Explanation
Carbon-composition resistors are comparatively nonreactive because they have a relatively low level of inductance and capacitance in addition to their resistance. This means that they do not significantly affect the performance of a circuit by introducing unwanted reactance. As a result, carbon-composition resistors are commonly used in applications where stability and low reactance are important, such as in audio circuits or high-frequency applications.
5.
The best place to use a wirewound resistor is:
Correct Answer
D. In a high-power, direct-current circuit
Explanation
A wirewound resistor is designed to handle high power levels and is capable of dissipating heat effectively. In a high-power, direct-current circuit, where there is a significant amount of power being transferred and dissipated, a wirewound resistor would be the best choice. It can handle the high power and provide accurate resistance values without overheating. In other applications such as a radio-frequency amplifier or when the resistor doesn't dissipate much power, other types of resistors may be more suitable.
6.
A metal-film resistor:
Correct Answer
B. Has less reactance than a wirewound type
Explanation
A metal-film resistor has less reactance than a wirewound type because the metal film resistor is made using a thin layer of metal deposited on a ceramic or glass substrate. This design allows for a shorter and more direct path for the current to flow, resulting in lower reactance. In contrast, a wirewound resistor is made by winding a wire around a ceramic or fiberglass core, which introduces more length and therefore higher reactance.
7.
A meter-sensitivity control in a test instrument would probably be:
Correct Answer
B. A linear-taper potentiometer
Explanation
A linear-taper potentiometer would be the most likely choice for a meter-sensitivity control in a test instrument. This is because a potentiometer allows for precise control of resistance, which can be used to adjust the sensitivity of the meter. A linear-taper potentiometer would provide a linear change in resistance as the control is adjusted, allowing for fine-tuning of the sensitivity. Switchable, fixed resistors would not provide the same level of adjustability, and a logarithmic-taper potentiometer may not offer the desired linear response. A wirewound resistor is not typically used for this purpose.
8.
A volume control in a stereo compact-disc player would probably be:
Correct Answer
C. A logarithmic-taper potentiometer
Explanation
A logarithmic-taper potentiometer is the most suitable volume control for a stereo compact-disc player because it provides a logarithmic relationship between the position of the potentiometer and the loudness of the audio output. This is important because human perception of loudness is logarithmic, meaning that doubling the power does not result in a perceived doubling of loudness. Therefore, a logarithmic-taper potentiometer allows for more precise control over the volume levels, ensuring a smoother and more accurate adjustment of the audio output.
9.
If a sound triples in actual power level, approximately what is the decibel increase?
Correct Answer
B. 5 dB
Explanation
When a sound triples in actual power level, the decibel increase can be calculated using the formula: dB increase = 10 * log10 (power ratio). In this case, the power ratio is 3 (tripling the power level), so the dB increase would be approximately 10 * log10 (3) = 4.77 dB. Since the answer choices are limited, the closest option is 5 dB.
10.
Suppose a sound changes in volume by -13 dB. If the original sound power is 1 W, what is the final sound power?
Correct Answer
C. 50 mW
Explanation
The sound changes in volume by -13 dB, which means it decreases in power. The final sound power can be calculated using the formula: Final Power = Original Power * 10^(dB change/10). In this case, the original power is 1 W and the dB change is -13 dB. Plugging in these values, we get: Final Power = 1 W * 10^(-13/10) = 0.050 W = 50 mW. Therefore, the final sound power is 50 mW.
11.
The sound from a transistor radio is at a level of 50 dB. How many times the threshold of hearing is this, in terms of actual sound power?
Correct Answer
D. 100,000
Explanation
The threshold of hearing is the minimum sound level that can be detected by the human ear. It is typically defined as 0 decibels (dB). In this question, the sound from a transistor radio is at a level of 50 dB. The relationship between decibels and actual sound power is logarithmic, with each increase of 10 dB representing a tenfold increase in sound power. Therefore, if the sound from the transistor radio is 50 dB, it is 10^5 times (or 100,000 times) the threshold of hearing in terms of actual sound power.
12.
An advantage of a rheostat over a potentiometer is that:
Correct Answer
C. A rheostat can handle more current
Explanation
A rheostat is designed to handle higher currents compared to a potentiometer. This is because a rheostat is specifically designed to control and vary the amount of current flowing through a circuit, while a potentiometer is primarily used to control voltage. Therefore, when higher current levels are required, a rheostat is preferred as it can handle and regulate the flow of more current effectively.
13.
A resistor is specified as having a value of 68 Ω, but is measured with an ohmmeter as 63 Ω. The value is off by:
Correct Answer
A. 7.4 percent
Explanation
The value of the resistor is off by 7.4 percent. This can be calculated by finding the difference between the measured value (63 Ω) and the specified value (68 Ω), which is 5 Ω. Then, divide this difference by the specified value and multiply by 100 to get the percentage. In this case, (5/68) * 100 = 7.4 percent.
14.
Suppose a resistor is rated at 3.3 K Ω, plus or minus 5 percent. This means it can be expected to have a value between:
Correct Answer
C. 3,135 and 3,465 Ω
Explanation
The correct answer is 3,135 and 3,465 Ω. This is because the resistor is rated at 3.3 KΩ, which means it has a nominal value of 3,300 Ω. The plus or minus 5 percent tolerance indicates that the actual value of the resistor can vary by 5 percent in either direction. Therefore, the minimum value would be 3,300 Ω - (3,300 Ω * 0.05) = 3,135 Ω, and the maximum value would be 3,300 Ω + (3,300 Ω * 0.05) = 3,465 Ω.
15.
A package of resistors is rated at 56 Ω, plus or minus 10 percent. You test them with an ohmmeter. Which of the following values indicates a reject?
Correct Answer
A. 50.0 Ω
Explanation
The package of resistors is rated at 56 Ω, plus or minus 10 percent. This means that the acceptable range for the resistors is 56 Ω ± 10%, which is 50.4 Ω to 61.6 Ω. Therefore, any value outside of this range would indicate a reject. The value of 50.0 Ω is outside of the acceptable range, so it indicates a reject.
16.
A resistor has a value of 680 Ω, and you expect it will have to draw 1 mA maximum continuous current. What power rating is best for this application?
Correct Answer
A. 1/4 W
Explanation
The power rating of a resistor indicates the maximum amount of power it can safely dissipate without overheating. In this case, the resistor has a value of 680 Ω and is expected to draw a maximum continuous current of 1 mA. To calculate the power rating, we can use the formula P = I^2 * R, where P is the power, I is the current, and R is the resistance. Plugging in the values, we get P = (0.001 A)^2 * 680 Ω = 0.00068 W, which is less than 1/4 W. Therefore, the best power rating for this application is 1/4 W.
17.
Suppose a 1-K Ω resistor will dissipate 1.05 W, and you have many 1-W resistors of all common values. If there’s room for 20-percent resistance error, the cheapest solution is to use:
Correct Answer
B. Two 2.2 K Ω, 1-W resistors in parallel
Explanation
The cheapest solution is to use two 2.2 K Ω, 1-W resistors in parallel because when resistors are connected in parallel, the total resistance decreases. In this case, the two 2.2 K Ω resistors in parallel will give a total resistance of 1.1 K Ω, which is within the 20-percent resistance error allowed. Additionally, each resistor is 1-W, so the total power dissipation will be 2-W, which is higher than the required 1.05 W. Therefore, this solution meets the requirements while being the most cost-effective.
18.
Red, red, red, gold indicates a resistance of:
Correct Answer
B. 220 Ω
Explanation
The colors red, red, red indicate a value of 22 in the resistor color code. Since there is a gold band after the red, red, red bands, it signifies that the value should be multiplied by a factor of 0.1. Therefore, 22 * 0.1 equals 2.2. The unit of measurement for resistance is ohms, so the final answer is 2.2 K Ω, which stands for 2.2 kiloohms.
19.
A resistor has three bands: gray, red, yellow. This unit can be expected to have a value within approximately what range?
Correct Answer
A. 660 K Ω to 980 K Ω
Explanation
The three bands on the resistor indicate the resistor's value using the color code system. The first band is gray, which represents the digit 8. The second band is red, which represents the digit 2. The third band is yellow, which represents a multiplier of 10^4. Combining these digits and multiplier, we get a value of 82 x 10^4 Ω, which is equal to 820,000 Ω or 820 K Ω. The tolerance of the resistor is not given, so we cannot determine the exact range. However, based on the given options, the closest range to 820 K Ω is 660 K Ω to 980 K Ω.
20.
The actual resistance of the above unit can be expected to vary by how much above or below the specified value?
Correct Answer
A. 11 Ω
Explanation
The actual resistance of the unit can be expected to vary around the specified value of 11 Ω