Physics MCQs for NEET — Practice Questions with Answers

p-type semiconductor are obtained by adding a small amount of trivalent impurity to a pure sample of semiconductor(Ge).

Majority charge carriers-holes

Minority charge carries-electrons

n-type semiconductor are obtained by adding a small amount of pentavalent impurity to a pure sample of semiconductor (Ge).

Majority charge carries-electrons

The resistance of intrinsic semiconductors decreases with increase of temperature.

Integrated circuits are miniature electronic circuit produced within a single crystal of a semiconductors such as silicon. They contain a million or so transistors and resistors or capacitors. They are widely used in memory circuits, micro computers, pocket calculators and electronic watches on account of their low cost and bulk, reliability into specific regions of the semiconductor crystals.

Key Idea    Only signals having wavelength less than threshold wavelength will be detected.

 $$\begin{gathered} \mathrm{Energy} \mathrm{E}=\mathrm{hv}=\mathrm{h}\frac{\mathrm{c}}{\mathrm{\lambda }} \\ \Rightarrow \mathrm{\lambda }=\frac{\mathrm{hc}}{\mathrm{E}} \end{gathered}$$

Substituting the value of h, c and E in the above equation 

                  $\mathrm{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{2.5\times 1.6\times {10}^{-19}}=5000 \stackrel{\circ }{\mathrm{A}}$

   As  $4000 \stackrel{\circ }{\mathrm{A}}<5000 \stackrel{\circ }{\mathrm{A}}$

 Signal of wavelength $4000 \stackrel{\circ }{\mathrm{A}}$ can be detected by the photodiode.

Neighbour distance of a body centred cubic cell $d=\frac{\sqrt{3}}{2}a, where a is the lattice parameter.$

$\Rightarrow 3.7=\frac{\sqrt{3}a}{2}$

or               $a=\frac{2\times 3.7}{\sqrt{3}}=4.3\stackrel{0}{A}$

Atomic radius is the distance between two nearest neighbours. For fcc crystal

Atomic radius = $\frac{1}{2\sqrt{2}}\times lattice parameter$

or               $r=\frac{a}{2\sqrt{2}}$

or             $r=\frac{3.6}{2\sqrt{2}} \stackrel{0}{A}=1.27 \stackrel{0}{A}$

(b) In forward biasing the P-end is connected to the positive terminal of the battery.

(a) In forward biased PN-junction, external voltage decreases the potential barrier, so current is maximum. While in reversed biased PN-junction, external voltage increases the potential barrier, so the current is very small

(b) The cut in voltage for silicon diode = 0.6 V

(b) Filter circuits are used to get smooth dc $\mathrm{\pi }$ -filter is the best filter.

(c) In reverse bias no current flows.