A PN junction diode is reverse biased when its P-terminal (anode) is connected to the negative terminal of the supply and its N-terminal (cathode) is connected to the positive terminal. Under reverse bias, the depletion layer widens, preventing the flow of current through the diode. Therefore, the current flowing through the resistor is 0 A.At the PN junction, a potential depletion layer is formed. The N-side remains at a higher potential, while the P-side remains at a lower potential. Consequently, the electric field across the junction is directed from the N-side to the P-side.
A Light Emitting Diode (LED) is a PN junction diode that emits light when activated. The colour of the light emitted depends upon the type of semiconductor material used in the LED.
A photodiode normally operates under reverse bias. Reverse bias enables the device to respond effectively to incident light.
A Field Effect Transistor (FET) is a voltage-controlled device having very high input impedance due to the reverse-biased gate junction.
A MOSFET is used in the first stage of an electronic voltmeter because it provides very high input impedance and low input current.
The base region of a transistor is lightly doped.
In an N-type semiconductor, the donor energy level lies closely below the bottom of the conduction band.
The MOD (modulus) of a Johnson counter using n flip-flops isMOD = 2nHence,
For an n-bit counter,
The NAND gate and NOR gate are known as Universal Gates because any logic circuit can be implemented using only these gates.
The 8051 Microcontroller contains the following internal resources:
| Component | Specification |
|---|---|
| Internal RAM (Data Memory) | 128 Bytes |
| Internal ROM / Flash (Code Memory) | 4 KB |
| Timers/Counters | 2 |
| Interrupts | 5 |
| I/O Pins | 32 |
| Serial Port | 1 |
Read and Write operations are mainly performed by RAM (Random Access Memory).
In the binary (base-2) system,1 Megabyte (MB) = 2²⁰ Bytes.
An electronic voltmeter is essentially a very stable DC voltage amplifier having a vacuum-tube input stage, which provides high input impedance and low grid current. In modern electronic voltmeters, a MOSFET is used in the first stage because of its high input impedance.
An Integrating Digital Voltmeter (DVM) measures the true average value of the input voltage.
For displaying a sine wave on a CRO, a saw-tooth waveform is applied to the horizontal plates.The purpose of synchronizing control in a CRO is to lock the display of the signal, thereby producing a stable waveform on the screen.
The major difference between a current probe and a voltage probe is that a current probe provides a method of inductive coupling.
The internal reference voltage of IC 723 is 7 V.
An ideal regulated power supply has 0% voltage regulation.
A full-wave bridge rectifier consists of four diodes connected in a bridge configuration. It converts the entire AC input waveform into pulsating DC, thereby utilizing both half cycles of the input signal.
An ideal regulated power supply has 0% voltage regulation, indicating that the output voltage remains constant irrespective of changes in load current.
The power factor of a D.C. circuit is always Unity (1) because the voltage and current are always in phase.
The energy efficiency of a battery is defined as the ratio of the electrical energy supplied by the battery during discharge to the electrical energy required to restore it to its original charged state.
An electrical motor is an electrical device that receives electrical energy at the electrical port and delivers mechanical energy at the mechanical port. Thus, it converts electrical energy into mechanical energy.
A Permanent Magnet type instrument is suitable for D.C. measurements only, as its direction of deflection depends on the direction of current.
An induction type single-phase energy meter measures electrical energy in kilowatt-hour (kWh).
When the pointer of an indicating instrument is in motion, the deflecting torque is opposed by the controlling torque, which brings the pointer to its final steady position.
In a thyristor, the minimum current required to keep the device in the ON state after triggering is known as the Holding Current.
A good heating element should possess:
These properties enable efficient heat production while withstanding high operating temperatures.
The suitable methods for measuring resistance are:
| Type of Resistance | Measurement Method |
|---|---|
| High Resistance | Megger Circuit, Loss of Charge Method |
| Medium Resistance | Substitution Method, Ohmmeter, Wheatstone Bridge |
| Low Resistance | Kelvin Double Bridge, Potentiometer Method, Ammeter–Voltmeter Method |
Different bridges are preferred depending upon the Quality Factor (Q) of the inductor.
| Q Value | Bridge Used |
|---|---|
| High Q | Hay's Bridge |
| Medium Q | Maxwell Inductance-Capacitance Bridge |
| Low Q | Owen's Bridge, Anderson Bridge |
Different bridges are used depending upon the type of capacitor.
| Capacitor Type | Bridge Used |
|---|---|
| Lossy Capacitor | Schering Bridge |
| Lossless Capacitor | De-Sauty's Bridge |
The Wien Bridge is used for the measurement of frequency.
De-Sauty's Bridge is most suitable for the measurement of capacitance. In this bridge, balance is obtained only when both capacitors are perfect (lossless).
A Megohmmeter (Megger) is an electrical instrument used for measuring very high resistance values. It works by applying a high-voltage signal across the object being tested.
The unit of capacitive reactance is Ohm (Ω).
One important advantage of modulation is that it enables the use of a smaller antenna, making communication systems more practical and efficient.
The process of recovering the original information signal from the received modulated carrier wave is called Demodulation.
The following are examples of digital communication techniques:
In a superheterodyne receiver, the incoming radio frequency signal is converted into a fixed Intermediate Frequency (IF) for easier amplification and processing.A local oscillator is used to tune the receiver to a specific frequency by producing a frequency that mixes with the incoming signal.
Radio waves (short waves) are widely used for the wireless transmission of sound, messages, and information. They are also extensively used in maritime communication and aircraft navigation.
The Thermosphere is the atmospheric layer that contains a large number of ions. This ionized region assists in wireless communication by reflecting radio waves.
In practice, voltage gain is expressed in Decibels (dB).
The change in the output waveform from the input waveform of an amplifier is known as Distortion.
For sustained oscillations, the following conditions must be satisfied:
These are the required conditions for continuous oscillation.
The output waveform of an integrator in a function generator is a Triangular Wave.
Tactile sensors provide a robot with the capability to respond to contact forces between itself and other objects present within its work area. They enable the robot to detect physical touch or contact and react accordingly.
Eddy current sensors are used to detect the presence of non-magnetic conductive materials, such as metals. Their operation is based on the generation of eddy currents in conductive objects.
Piezoelectric materials produce electrical energy when subjected to mechanical stress, such as compression or pressure. These materials also exhibit the reverse piezoelectric effect, in which they deform when an electric voltage is applied.
In an optical fibre, the refractive index of the cladding must always be less than that of the core. This difference in refractive indices allows light to remain confined within the core through internal reflection.
Liquid Crystal Displays (LCDs) consume very low power. A seven-segment LCD display requires approximately 140 μW (20 μW per segment), which is a significant advantage over LED displays that require approximately 40 mW per numeral.LCDs are also low in cost, making them suitable for a wide range of electronic applications.
LCDs have several limitations:
Thermocouple instruments can be used for both AC and DC measurements. They are suitable for measuring current as well as voltage at high frequencies and provide high accuracy even at frequencies well above 50 MHz.
A reverse proxy can maintain a cache of static content, thereby reducing the load on the internal servers as well as on the internal network. This improves the overall efficiency of network communication.
Read and Write operations are mainly performed by Random Access Memory (RAM).
In Microsoft Word, the Table Resize icon appears at the bottom-right corner of a table. It is used to resize the entire table.
In the binary number system,1 Megabyte (MB) = 2²⁰ Bytes.
Machine Drawing is used to communicate technical information to industry. It provides a standardized graphical representation of machine components and assemblies for manufacturing and production purposes.
When a line is parallel to a plane, its orthographic projection on that plane appears in its true length.
Boring is the machining operation used for enlarging and truing a hole that has already been produced by drilling, punching, casting, or forging.
A typical solder used for assembling electronic components on a Printed Circuit Board (PCB) consists of Lead and Tin.
A Halon fire extinguisher is suitable for extinguishing live electrical fires because it does not conduct electricity and does not damage electrical equipment.
When electric current passes through a conducting solution, a chemical reaction takes place. As a result, changes such as the change in the colour of the solution may occur. This phenomenon is known as the chemical effect of electric current.
The working principle of an electric bell involves the conversion of electrical energy into sound energy.
The frequency to which the incoming signal is converted in a superheterodyne receiver is known as the Intermediate Frequency (IF).
A local oscillator is used to tune a radio receiver to a desired frequency by generating the required oscillating signal.
Radio waves (short waves) are used for the wireless transmission of sound, messages, and information. They are also widely used for maritime communication and aircraft navigation.
The Thermosphere contains a large number of ions, which assist in wireless communication by supporting the propagation of radio waves.
| Topic | Important Fact |
|---|---|
| Reverse Biased Diode | Current = 0 A |
| LED | Emits light; colour depends on semiconductor material |
| Photodiode | Operates under Reverse Bias |
| FET | Voltage-controlled, high input impedance |
| MOSFET | Used in first stage of electronic voltmeter |
| 8051 | 128 B RAM, 4 KB ROM, 2 Timers, 5 Interrupts, 32 I/O Pins |
| Johnson Counter | MOD = 2n, Flip-flops required = n/2 |
| Universal Gates | NAND, NOR |
| Bridge Rectifier | Four diodes |
| Power Factor (DC) | Unity |
| Holding Current | Minimum current to keep SCR ON |
| Capacitive Reactance Unit | Ohm (Ω) |
| Voltage Gain | Expressed in dB |
| Integrator Output | Triangular Wave |
| Demodulation | Recovery of information signal |
| ASK, FSK, PSK, QAM | Digital communication techniques |
| Optical Fibre | Cladding refractive index < Core |
| PMMC Instrument | DC only |
| Energy Meter | Measures kWh |
| Machine Drawing | Communicates information to industry |
| Boring | Enlarges and trues an existing hole |
| Megger | Measures very high resistance |
| Thermocouple Instrument | Suitable for AC and DC, high-frequency measurements |
| Halon Extinguisher | Suitable for live electrical fires |
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