Advertisements
Advertisements
Question
Colour of light emitted by LED depends upon__________________ .
- its forward bias
- its reverse bias
- the band gap of the material of semiconductor
- its size
Advertisements
Solution
the band gap of the material of semiconductor
APPEARS IN
RELATED QUESTIONS
How is a Zener diode fabricated?
Explain with the help of a diagram, how depletion region and potential barrier are formed in a junction diode.
If a small voltage is applied to a p-n junction diode, how will the barrier potential be affected when it is(ii) reveres biased?
Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in
Forward biasing
How are these characteristics made use of in rectification?
Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in
Reverse biasing
How are these characteristics made use of in rectification?
Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)C, (Eg)Si and (Eg)Ge. Which of the following statements is true?
A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?
State its any ‘two’ uses of photodiode.
Describe, with the help of a circuit diagram, the working of a photodiode.
Sunil and his parents were travelling to their village in their car. On the way his mother noticed some grey coloured panels installed on the roof of a low building. She enquired from Sunil what those panels were and Sunil told his mother that those were solar panels.
(a) What were the values displayed by Sunil and his mother? State one value for each.
(b) In what way would the use of solar panels prove to be very useful?
(c) Name the semiconductor device used in solar panels. Briefly explain with the help of a diagram, how this device works
Why is zener diode fabricated by heavily doping both p- and n-sides of the junction?
Draw V − I characteristics of a p-n junction diode. Answer the following questions, giving reasons:
(i) Why is the current under reverse bias almost independent of the applied potential up to a critical voltage?
(ii) Why does the reverse current show a sudden increase at the critical voltage?
Name any semiconductor device which operates under the reverse bias in the breakdown region.
The current in the forward bias is known to be more (~mA) than the current in the reverse bias (~μA). What is the reason, then, to operate the photodiode in reverse bias?
Draw the circuit diagram of a full wave rectifier using p-n junction diode.
Explain its working and show the output, input waveforms.
What happens to the width of depletion player of a p-n junction when it is (i) forward biased, (ii) reverse biased?
Explain the formation of depletion layer and potential barrier in a p−n junction.
The plate resistance of a triode is 8 kΩ and the transconductance is 2.5 millimho. (a) If the plate voltage is increased by 48 V and the grid voltage is kept constant, what will be the increase in the plate current? (b) With plate voltage kept constant at this increased value, by how much should the grid voltage be decreased in order to bring the plate current back to its initial value?
Write the important considerations which are to be taken into account while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED, if it is required to emit light in the visible range? Draw a circuit diagram and explain its action.
Write the important considerations which are to be taken into account while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of the band gap of an LED, if it is required to emit light in the visible range? Draw a circuit diagram and explain its action.
The wavelength and intensity of light emitted by a LED depend upon ______.
Draw solar cell V-I characteristics.
Explain the three processes involved in the working of a solar cell.
With reference to Semiconductor Physics,
Name the process that causes depletion region in a p-n junction.
Explain photodiode.
What is the magnitude of the potential barrier across a Ge p-n junction?
Name the device which converts the change in intensity of illumination to change in electric current flowing through it. Plot I-V characteristics of this device for different intensities. State any two applications of this device.
Pressure P varies as P = `alpha/beta "exp" (- (alpha x)/"k"_"BT")`, where x denotes the distance, kB is the Boltzmann's constant, T is the absolute temperature and α and β are constant. The dimension of β is ______.
A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. lt can detect a signal of wavelength ______.
For LED's to emit light in visible region of electromagnetic light, it should have energy band gap in the range of:
Which one of the following is not the advantage of LED?
Consider the following statements (A) and (B) and identify the correct answer.
- A Zener diode is connected in reverse bias when used as a voltage regulator.
- The potential barrier of the p-n junction lies between 0.1 V to 0.3 V.
The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 and 30, respectively and the input signal is 1 mV peak value, then what is the output signal voltage (peak value)
- if dc supply voltage is 10V?
- if dc supply voltage is 5V?
If the resistance R1 is increased (Figure), how will the readings of the ammeter and voltmeter change?
Read the following paragraph and answer the questions.
|
LED is a heavily doped P-N junction which under forward bias emits spontaneous radiation. When it is forward-biased, due to recombination of holes and electrons at the junction, energy is released in the form of photons. In the case of Si and Ge diode, the energy released in recombination lies in the infrared region. LEDs that can emit red, yellow, orange, green and blue light are commercially available. The semiconductor used for fabrication of visible LEDs must at least have a band gap of 1.8 eV. The compound semiconductor Gallium Arsenide – Phosphide is used for making LEDs of different colours.
|
- Why are LEDs made of compound semiconductor and not of elemental semiconductors?
- What should be the order of bandgap of an LED, if it is required to emit light in the visible range?
- A student connects the blue coloured LED as shown in the figure. The LED did not glow when switch S is closed. Explain why?
OR
iii. Draw V-I characteristic of a p-n junction diode in
(i) forward bias and (ii) reverse bias
Draw solar cells of I-V characteristics.
Draw the circuit diagram of an illuminated photodiode and its I-V characteristics.
The value of power dissipated across the Zener diode (Vz = 15 V) connected in the circuit as shown in the figure is x × 10–1 watt. The value of x, to the nearest integer, is ______.
What energy conversion takes place in a solar cell?
A light emitting diode (LED) is fabricated using GaAs semiconducting material whose band gap is 1.42 eV. The wavelength of light emitted from the LED is ______.
Consider the following statements A and B and identify the correct answer:
- For a solar-cell, the I-V characteristics lies in the IV quadrant of the given graph.
- In a reverse biased pn junction diode, the current measured in (A), is due to majority charge carriers.
