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Electronics Engineering
Electronics Engineering is a branch of engineering that deals with practical applications of electronic components, devices, systems, or equipment. Electronics are devices that operate on low voltage sources, as in electron tubes, transistors, integrated circuits, and printed circuit boards and use electricity as part of its driving force.
24,372 Questions
UJT(UNIJUNCTION TRANSISTOR) is a three-lead electronic-semiconductor device with only one junction that exclusively as an eletrically controlled swtich andit is not used as a linear amplifier.
What is the relationship between Wattage and resistance of resistor?
There is no direct relationship.
Power ('wattage') is a measure of the rate at which the resistor can dissipate energy; excessive power means that a resistor cannot dissipate energy fast enough to prevent its temperature becoming excessive -excessive enough to damage the resistor.
As the rate at which a resistor can dissipate energy is determined by its physical size, a resistor's power rating(maximum continuous power it can handle without exceeding its rated temperature) depends on the physical size of the resistor.
On the other hand, the resistance of a resistor is notaffected by its physical dimensions, as a resistor can be manufactured to any particular value of resistance for whatever physical size is necessary to achieve its rated power.
If you know a resistor's rated power and its resistance, then you can calculate the maximum continuous current that resistor can handle without overheating (using the equation: power = current squared x resistance).
What is the relationship between frequency and antenna height?
For horizontal antennas operating below 30 MHz the optimum height is half a wavelength, so the height in metres would be 149.9/Frequency in MHz.
What is the difference between clippers and half-wave rectifiers?
A clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.
A clipping circuit consists of linear elements like resistors and non-linear elements like junction diodes or transistors but it does not contain energy-storage elements like capacitors. Clipping circuits are used to select for purposes of transmission, that part of a signal wave form which lies above or below a certain reference voltage level.
In half wave rectification of a single-phase supply, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in a single-phase supply , or three in a three-phase supply. Rectifiers yield a unidirectional but pulsating direct current; half-wave rectifiers produce far more ripple than full-wave rectifiers, and much more filtering is needed to eliminate harmonics of the AC frequency from the output.
Half-wave rectifier
The no-load output DC voltage of an ideal half wave rectifier for a sinusoidal input voltage is:
Where:
Vdc, Vav - the DC or average output voltage,Vpeak, the peak value of the phase input voltages,Vrms, the root-mean-square value of output voltage.
What is meant by wattless current?
Current flowing through an ac circuit in which power consumed is zero is called wattless current.
the resitance would be used to reduce a voltage amplitude to a level suitable to be used in an application, to limit the amount of current flowing within the circuit , or in some cases the resistor
could be used as a heating - effect.
Can we use a fluorescent lamp in DC?
Yes, fluorescent lamps may be powered by DC but they need a DC lamp controller instead of an AC ballast and starter. The DC lamp controller is more complex.
I have a 12V lantern with fluorescent lamp tubes.
Which component requires a constant electrical charge and a periodic refresh of the circuits?
While your question is unclear and shows that you are somewhat confused, I believe you are probably asking about Dynamic Random Access Memory (DRAM) devices. These devices store data as electrical charge in billions or trillions of microscopic capacitors. Because no insulator is perfect the charge in these capacitors slowly leaks off, meaning to avoid losing the date the memory must be refreshed by periodically reading every capacitor and writing it back.
I have no idea what you were thinking when you wrote "requires a constant electrical charge" as the charge on the capacitors when they need to be refreshed may be half or less of the charge on the capacitors when they were first written or after they have been refreshed. The charge on the capacitors is never constant, which is the reason they need refreshing in the first place.
The first Dynamic Memory was built in 1941 by John Vincent Atanasoff and Clifford Berry, it used capacitors but was not randomly accessible. It had a storage capacity of sixty 50 bit signed binary words and was refreshed once per second.
Later Dynamic Memories included delay line memories (both mechanical and electrical) and CRT DRAM that stored the charge as tiny spots on the inside face of the vacuum tube.
A Z-transform is a mathematical transform which converts a discrete time-domain signal into a complex frequency-domain representation.
What is active pull up in TTL NAND gate?
All standard TTL devices use a two transistor "totempole" output, one transistor provides an active pull down and the other an active pull up. Only one of these transistors is on at a time and one or the other is always on.
Open collector TTL devices omit the active pull up transistor so that several outputs can be "wired" together and an external resistor provides a passive pull up. The only problem with this is the risetime of a passive pullup is much longer than the risetime of an active pull up, making the circuit slower.
Tristate TTL devices have the same two transistor "totempole" output as standard TTL devices, but the circuits that control these transistors are more complex allowing a "third state" in which both transistors are turned off, leaving the output of the device floating. This allows many tristate TTL devices to be connected to a single line with only one actually driving it at a time (preventing conflicts with one device pulling up and another pulling down).
Why high voltage does not kill?
Its not voltage that kills it is current.
High voltage CAN kill, if it can also provide high current (especially if the current comes near the heart as it takes under 1mA to stop the heart which isn't much current).
However if the high voltage source is current limited and/or the current only passes through the extremities it is very unlikely to kill.
What kind of flip flop has no invalid or unused state?
None, all flip flops have a small probability of entering a metastable invalid state.
What is the potential difference if a resistance is 25 ohms produces current of 250 amperes?
E = I * R = 250 * 25 = 6500 volts
This resistor will be dissipating 156.25 kilowatts, which would vaporize most resistors instantly!!!!!
Who is responsible for determining the type of emf control measures required?
711th Human Performance Wing
Maximum power rating describes the maximum power at which a device can operate without reaching an excessive temperature. For example, in the case of a resistor, if its maximum power rating is exceeded, then it may burn out.
Why are subjective accounts often biased?
Because subjective accounts are opinionated and emotional, The narrator usually provides only one side of the story.
Why the armature current of a shunt motor decreases as the motor accelerates?
Without a mechanical load the motor accelerates until the back-emf generated by the armature nearly equals the supply voltage. On load, the speed drops and the current rises until the power taken from the supply balances the mechanical power supplied to the load.
If the armature has low resistance, the speed drop under load is not very much, so speed regulation is better if the armature resistance is lower.
What would happen if the lead of your voltmeter were connected backward?
A digital voltmeter will read negative voltage, if connecting backward.
If the meter is an analogue type, the needle will go backwards and dip below the 0 on the scale.
