Home
Class 12
PHYSICS
Give reasons for the following: (i) Hi...

Give reasons for the following:
(i) High reverse voltage do not appear across a LED. (ii) Sunlight is always required for the working of a solar cell.
(iii) The electric field, of the junction of a ener diode, is very high even for a small reverse bias voltage of about 5V.

Text Solution

Verified by Experts

(i) LED is a heavily doped p-n junction, when a reverse voltage is applied across LED, the minority carriers increase near the junction and current starts flowing. Due to it, the high reverse voltage do not appear across the junction.
(ii) It is so because the energy produced by solar cell can be stored in batteries for later use, when sunlight is not available.
(iii) Since depletion width of the junction of zener diode is very small `( lt 10^(-7)m)`, even a small voltage say 5V can set up a very high electric field as `E=V/d=5/10^(-7)=5xx10^(7) V//m`.
Promotional Banner

Topper's Solved these Questions

  • ELECTRONIC DEVICES

    PRADEEP|Exercise LONG QUESTION ANSWER|2 Videos

  • ELECTRONIC DEVICES

    PRADEEP|Exercise PROBLEMS FOR PRACTICE|7 Videos

  • ELECTRONIC DEVICES

    PRADEEP|Exercise HIGHER ORDER THINKING SKILLS|1 Videos

  • ELECTROMAGNETIC WAVES

    PRADEEP|Exercise II Focus multiple choice question|5 Videos

  • ELECTROSTATICS

    PRADEEP|Exercise ASSERTION-REASON TYPE QUESTIONS|2 Videos

Similar Questions

Explore conceptually related problems

Given reasons for the following : (i) High reverse voltage do not appear across a LED. (ii) Sunlight is not always required for the working of a solar cell. (iii) The electric field, of the junction of a Zener diode, is very high even for a small reverse bias voltage of about 5 V.

Read the following text and answer the following questions on the basis of the same: Light Emitting Diode: It is a heavily doped p-n junction which under forward bias emits spontaneous radiation. The diode is encapsulated with a transparent cover so that emitted light can come out. When the diode is forward biased, electrons are sent from n to p (where they are minority carriers) and holes are sent from p to n(where they are minority carriers). At the junction boundary, the concentration of minority carriers increases as compared to the equilibrium concentration (i.e., when there is no bias). Thus at the junction boundary on either side of the junction, excess minority carriers are there which recombine with majority carriers near the junction. On recombination, the energy is released in the form of photons. Photons with energy equal to or slightly less than the band gap are emitted. When the forward current of the diode is small, the intensity of light emitted is small. As the forward current increases, intensity of light increases and reaches a maximum. Further increase in the forward current results in decrease of light intensity. LED's are biased such that the light emitting efficiency is maximum. The V-I characteristics of a LED is similar to that of a Si junction diode. But, the threshold voltages are much higher and slightly different for each colour. The reverse breakdown voltages of LED's are very low, typically around 5 V. So care should be taken that high reverse voltages do not appear across them. LED's that can emit red, yellow, orange, green and blue light are commercially available. The reverse breakdown voltages of LED's are:

In the case of a p-n junction diode, if the reverse bias is very high, there is a sudden large increase in current. In this case the value of reverse bias voltage is known as

Consider the following statements A and B and identify the correct answer (A) A Zener diode is always connected in reverse bias to use it as voltage regulator. (B) The potential barrier of a p-n junction lies between 0.1 to 0.3 V , approximately.

Read the following text and answer the following questions on the basis of the same: Light Emitting Diode: It is a heavily doped p-n junction which under forward bias emits spontaneous radiation. The diode is encapsulated with a transparent cover so that emitted light can come out. When the diode is forward biased, electrons are sent from n to p (where they are minority carriers) and holes are sent from p to n(where they are minority carriers). At the junction boundary, the concentration of minority carriers increases as compared to the equilibrium concentration (i.e., when there is no bias). Thus at the junction boundary on either side of the junction, excess minority carriers are there which recombine with majority carriers near the junction. On recombination, the energy is released in the form of photons. Photons with energy equal to or slightly less than the band gap are emitted. When the forward current of the diode is small, the intensity of light emitted is small. As the forward current increases, intensity of light increases and reaches a maximum. Further increase in the forward current results in decrease of light intensity. LED's are biased such that the light emitting efficiency is maximum. The V-I characteristics of a LED is similar to that of a Si junction diode. But, the threshold voltages are much higher and slightly different for each colour. The reverse breakdown voltages of LED's are very low, typically around 5 V. So care should be taken that high reverse voltages do not appear across them. LED's that can emit red, yellow, orange, green and blue light are commercially available. Threshold voltage of LED is:

Read the following text and answer the following questions on the basis of the same: Light Emitting Diode: It is a heavily doped p-n junction which under forward bias emits spontaneous radiation. The diode is encapsulated with a transparent cover so that emitted light can come out. When the diode is forward biased, electrons are sent from n to p (where they are minority carriers) and holes are sent from p to n(where they are minority carriers). At the junction boundary, the concentration of minority carriers increases as compared to the equilibrium concentration (i.e., when there is no bias). Thus at the junction boundary on either side of the junction, excess minority carriers are there which recombine with majority carriers near the junction. On recombination, the energy is released in the form of photons. Photons with energy equal to or slightly less than the band gap are emitted. When the forward current of the diode is small, the intensity of light emitted is small. As the forward current increases, intensity of light increases and reaches a maximum. Further increase in the forward current results in decrease of light intensity. LED's are biased such that the light emitting efficiency is maximum. The V-I characteristics of a LED is similar to that of a Si junction diode. But, the threshold voltages are much higher and slightly different for each colour. The reverse breakdown voltages of LED's are very low, typically around 5 V. So care should be taken that high reverse voltages do not appear across them. LED's that can emit red, yellow, orange, green and blue light are commercially available. LED is a :

Read the following text and answer the following questions on the basis of the same: Light Emitting Diode: It is a heavily doped p-n junction which under forward bias emits spontaneous radiation. The diode is encapsulated with a transparent cover so that emitted light can come out. When the diode is forward biased, electrons are sent from n to p (where they are minority carriers) and holes are sent from p to n(where they are minority carriers). At the junction boundary, the concentration of minority carriers increases as compared to the equilibrium concentration (i.e., when there is no bias). Thus at the junction boundary on either side of the junction, excess minority carriers are there which recombine with majority carriers near the junction. On recombination, the energy is released in the form of photons. Photons with energy equal to or slightly less than the band gap are emitted. When the forward current of the diode is small, the intensity of light emitted is small. As the forward current increases, intensity of light increases and reaches a maximum. Further increase in the forward current results in decrease of light intensity. LED's are biased such that the light emitting efficiency is maximum. The V-I characteristics of a LED is similar to that of a Si junction diode. But, the threshold voltages are much higher and slightly different for each colour. The reverse breakdown voltages of LED's are very low, typically around 5 V. So care should be taken that high reverse voltages do not appear across them. LED's that can emit red, yellow, orange, green and blue light are commercially available. LED emits light:

PRADEEP-ELECTRONIC DEVICES-Exercise
  1. What is light emitting diode (LED) ? Mention two important advantages ...

    Text Solution

    |

  2. Mention the important considerations required while fabricating a p-n ...

    Text Solution

    |

  3. Give reasons for the following: (i) High reverse voltage do not appe...

    Text Solution

    |

  4. Write the function of three segments of a transistor.

    Text Solution

    |

  5. Sketch the three modes of study of n-p-n junction transistor.

    Text Solution

    |

  6. Explain that a transistor can be used as a switch.

    Text Solution

    |

  7. Discuss briefly the concept of an amplifier.

    Text Solution

    |

  8. Draw a circuit diagram of a transistor amplifier in CE configuration. ...

    Text Solution

    |

  9. Explain the advantages and disadvantages of semiconducting devices com...

    Text Solution

    |

  10. Give the logic symbol, truth table and Boolean expression for OR gate....

    Text Solution

    |

  11. Give the logic symbol, truth table and Boolean expression for AND gate...

    Text Solution

    |

  12. How is NOT gate realised? Explain.

    Text Solution

    |

  13. What is logic gate? Distinguish between AND and OR gates.

    Text Solution

    |

  14. What are main logic gates? How many types are they? Draw their symbols...

    Text Solution

    |

  15. Two signals A, B as given below are applied to (i) AND (ii) NOR and (i...

    Text Solution

    |

  16. Give the logic symbol, Boolean expression and truth table of NAND gate...

    Text Solution

    |

  17. Identify the logic gate equivalent to the circuit shown in the Fig.Dra...

    Text Solution

    |

  18. Discuss an integrated circuit. Explain the meaning of SSI, MSI, LSI an...

    Text Solution

    |

  19. What is integrated circuit ? Discuss the advantages of integrated circ...

    Text Solution

    |

  20. Explain formation of energy band in solids. Distinguish between conduc...

    Text Solution

    |