Question: Q. 3. (i) In the following diagram ’ $S$ ’ is a semiconductor. Would you increase or decrease the value of $R$ to keep the reading of the ammeter A constant when $S$ is heated? Give reasôn for your answer.
(ii) Draw the circuit diagram of a photodiode and explain its working. Draw its $I / V$ characteristics. U] [OD III 2017]
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Solution:
Ans. (i) Correct Choice of $R$ ….. $1 / 2$ Reason ….. $1 / 2$ (ii) Circuit Diagram ….. 1 Working ….. $1 / 2$ I- $V$ characteristics ….. $1 / 2$ (i) $R$ would be increased. ….. $1 / 2$ Resistance of $S$ (a semiconductor) decreases on heating. ….. $1 / 2$
(ii) Photodiode diagram
1
When the photodiode is illuminated with light (photons) (with energy ( $h v$ ) greater than the energy gap $\left(E_{g}\right)$ of the semiconductor), then electronhole pairs are generated due to the absorption of photons. Due to junction field, electrons and holes are separated before they recombine. Electrons are collected on $n$-side and holes are collected on $p$-side giving rise to an emt.
$1 / 2$
When an external load is connected, current flows. $I-V$ Characteristics of the diode :
[CBSE Marking Scheme 2017]
