12th Class Physics Sample Paper Physics Sample Paper-4

  • question_answer
    A seminar was conducted on renewable sources of energy, where Romilla gave an motivating speech on 'solar cell' to create awareness among students guided by her Physics teacher.
    Read the above passage and answer the following questions :
    (i) State the reason, why GaAs is most commonly used in making a solar cell.
    (ii) What values are exhibited by Romilla?
    (iii) How does photocurrent is produced by solar cells?


                (i) For fabricating solar cell, incident photon energy must be greater than band gap energy, i.e. \[(hv>{{E}_{g}}).\] For GaAs, \[{{E}_{g}}=1.43\,eV\] and high optical absorption \[\approx {{10}^{4}}c{{m}^{-1}},\] which are the main criteria for fabrication of solar cell. (ii) Community service, scientific awareness and a good student. (iii) When photon of light \[(hv>{{E}_{g}})\] falls at the GaAs p-n junction, electron-hole pairs are generated near the junction and move in opposite directions due to junction field. A photovoltage will be produced between the top and bottom metal electrodes acting as positive and negative terminal producing photocurrent, supplies it to load connected externally.

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