1.
The gate-source voltage at which the ________________ layer in a MOSFET is formed is called the ________________ voltage.
Correct Answer
A. Inversion,threshold
Explanation
In a MOSFET, the gate-source voltage at which the inversion layer is formed is called the threshold voltage. The inversion layer is created when the gate-source voltage is sufficient to attract carriers to the channel region, allowing current to flow. The threshold voltage determines the point at which the MOSFET switches on and starts conducting.
2.
Transition Frequency of an MOSFET , fH is
Correct Answer
B. 1/2π* gm /(Cgs+Cgd)
Explanation
The transition frequency of an MOSFET, fH, is determined by the formula 1/2Ï€ * gm /(Cgs+Cgd). This formula takes into account the transconductance (gm) and the total gate capacitance (Cgs+Cgd) of the MOSFET. The transition frequency represents the frequency at which the MOSFET's gain starts to decrease. Therefore, the correct answer is 1/2Ï€ * gm /(Cgs+Cgd) because it accurately reflects the relationship between the transconductance and the total gate capacitance in determining the transition frequency of an MOSFET.
3.
In a low-pass filter consisting of a resistor and a capacitor, how will the cut-off frequency change if the capacitance is increased?
Correct Answer
C. Cut-off frequency decreases
Explanation
When the capacitance in a low-pass filter is increased, the cut-off frequency decreases. This is because the cut-off frequency is inversely proportional to the product of the resistance and the capacitance in the filter. As the capacitance increases, the product of resistance and capacitance decreases, resulting in a lower cut-off frequency.
4.
Which is a primary disadvantage of a solid-state amplifier compared with a vacuum-tube amplifier?
Correct Answer
C. Both a) & b)
Explanation
A solid-state amplifier has a primary disadvantage compared to a vacuum-tube amplifier in that it has poor tolerance for both low-current and -voltage transients as well as high-current and -voltage transients. This means that it does not handle sudden changes in current or voltage well, regardless of whether they are low or high.
5.
A transistor has a current gain of 0.5 in the CB mode. Its current gain in the CC mode is:
Correct Answer
A. 2
Explanation
In the common base (CB) mode, the current gain of the transistor is given as 0.5. The current gain in the common collector (CC) mode is typically higher than in the CB mode. Therefore, it is reasonable to expect that the current gain in the CC mode would be greater than 0.5. Among the given options, the only value greater than 0.5 is 2. Hence, the correct answer is 2.
6.
An LED has a rating of 4V and 100 mA. It is used along with a 12V battery. The range of series resistance is:
Correct Answer
A. 0 to 200
Explanation
The LED has a rating of 4V and 100 mA. To calculate the required resistance, we can use Ohm's law (V = IR), where V is the voltage across the resistor, I is the current flowing through the resistor, and R is the resistance. The voltage across the resistor is the difference between the battery voltage (12V) and the LED voltage (4V), which is 8V. The current flowing through the resistor is the same as the LED current, which is 100 mA. Plugging these values into Ohm's law, we get R = V/I = 8V / 0.1A = 80 ohms. Therefore, the range of series resistance is 0 to 200 ohms.
7.
What is the standard sound pressure for defining Signal to Noise ratio of microphones?
Correct Answer
A. 0.1 Pa
Explanation
The standard sound pressure for defining the Signal to Noise ratio of microphones is 0.1 Pa. This means that the microphone can accurately detect and differentiate sounds that have a signal level of 0.1 Pa or higher, while minimizing the detection of background noise. A lower value would indicate a lower sensitivity to capturing sounds, while a higher value may result in more interference from ambient noise.
8.
Zener diode can be used as _____
Correct Answer
C. Both AC and DC regulator
Explanation
A Zener diode can be used as both an AC and DC voltage regulator. It is commonly used to regulate voltage in electronic circuits by maintaining a constant voltage across its terminals, regardless of changes in input voltage or load resistance. In AC voltage regulation, the Zener diode is used to stabilize the output voltage by limiting voltage spikes and fluctuations. In DC voltage regulation, the Zener diode is used to provide a stable reference voltage or to protect sensitive components from excessive voltage. Therefore, the Zener diode can function as a regulator for both AC and DC circuits.
9.
A galvanometer in series with a high resistance is called?
Correct Answer
A. Ammeter
Explanation
A galvanometer in series with a high resistance is called an ammeter. This is because an ammeter is used to measure the flow of electric current in a circuit, and by adding a high resistance in series with the galvanometer, the current passing through the galvanometer is reduced and it can be used to measure larger currents accurately. A voltmeter is used to measure voltage, a wattmeter is used to measure power, and none of the above options fit the description given in the question.
10.
BC147 transistor indicates that it is made of:
Correct Answer
B. Silicon
Explanation
The BC147 transistor is made of silicon. Transistors are semiconductor devices that are commonly made from materials such as silicon or germanium. Silicon is the most widely used material for transistor production due to its abundance, stability, and ability to handle high temperatures. Germanium can also be used, but it is less commonly used compared to silicon. Carbon is not used in the production of transistors. Therefore, the correct answer is silicon.
11.
A 1000V power supply would use ___ as a filter capacitor.
Correct Answer
A. Paper capacitor
Explanation
A 1000V power supply would use a paper capacitor as a filter capacitor because paper capacitors are commonly used in high voltage applications. They have good insulation properties and can handle high voltage levels without breaking down. Paper capacitors are also known for their stability and reliability, making them suitable for use in power supply applications where a stable and reliable filtering component is required.
12.
A telephone exchange has 10000 subscribers. If the number of calls originating at peak time is 8000 in one hour, the calling rate is
Correct Answer
C. 4/5
Explanation
The calling rate can be calculated by dividing the number of calls originating at peak time (8000) by the total number of subscribers (10000). This gives us a calling rate of 0.8, which is equivalent to 4/5.