ISRO HSFC Technician B Electrician Solved Question paper

BJT (Bipolar Junction Transistor) is not a voltage-controlled device.

• MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and JFET (Junction Field Effect Transistor) are both voltage-controlled devices. Their conductivity is controlled by applying voltage to their gate terminals.
• IGBT (Insulated Gate Bipolar Transistor) is also a voltage-controlled device. It combines the high input impedance of a MOSFET with the high current output handling capability of a BJT, controlled by the voltage applied to its gate.
• BJT (Bipolar Junction Transistor), however, is current-controlled. The amount of current flowing through the collector is primarily determine by the base current.

• Ampere-hour efficiency = 0.85
• Average terminal voltage during discharging (V_discharge) = 2.1 V
• Average terminal voltage during charging (V_charge) = 2.55 V

Understanding Ampere-Hour Efficiency:

• Ampere-hour efficiency is the ratio of the ampere-hour capacity of a battery on discharge to its ampere-hour capacity on charge. It represents the efficiency of the battery in storing and delivering electrical energy.

Calculating Watt-Hour Efficiency:

• Watt-hour efficiency takes into account both the ampere-hour efficiency and the voltage changes during charging and discharging. It’s calculated as follows:

Watt-hour efficiency = Ampere-hour efficiency × (V_discharge / V_charge)

Substituting the given values:

• Watt-hour efficiency = 0.85 × (2.1 V / 2.55 V)

Calculating the result:

Watt-hour efficiency = 0.85 × 0.8235 ≈ 0.7

Given:

cos(x) = sin(60°) * sin(30°) + cos(60°) * cos(30°)

We know the following trigonometric values:

• sin(60°) = √3/2
• cos(60°) = 1/2
• sin(30°) = 1/2
• cos(30°) = √3/2

Substituting these values into the equation:

cos(x) = (√3/2) * (1/2) + (1/2) * (√3/2)

Simplifying:

cos(x) = √3/4 + √3/4

cos(x) = 2√3/4

cos(x) = √3/2

Now, we need to find the angle x whose cosine is √3/2.

From the unit circle or trigonometric table, we know that:

cos(30°) = √3/2

Therefore,

x = 30°

A low-pass filter is a type of electronic filter that allows signals with a frequency lower than a certain cutoff frequency to pass through while attenuating signals with frequencies higher than the cutoff frequency.

How it Works:

• Low-Frequency Signals: At low frequencies, the capacitor’s reactance (Xc) is high.
  • This means the capacitor acts as an open circuit, and most of the signal passes through the resistor and the load.
• High-Frequency Signals: At high frequencies, the capacitor’s reactance decreases.
  • The capacitor acts more like a short circuit, shunting most of the signal to ground.

Key Points:

• Cutoff Frequency: The frequency at which the filter starts to attenuate the signal is known as the cutoff frequency. It is determined by the values of R and C.

The electrolyte used in a nickel-cadmium battery is potassium hydroxide (KOH). It consist of 30% solution of potassium hydroxide (KOH) in distilled water.

Potassium Hydroxide (KOH):

• Conductivity: KOH is a strong electrolyte, providing good conductivity for the movement of ions within the battery.
• Chemical Reactions: It participates in the electrochemical reactions at the electrodes, facilitating the transfer of ions between the anode and cathode.

Distilled Water:

• Solvent: Distilled water acts as a solvent for the KOH, creating an aqueous solution.
• Ion Transport: It helps in the transport of ions between the electrodes, ensuring smooth operation of the battery.