Question

An LED is made of GaPo.24so8 and emits green light photons. What color is the following LED: GaPo As04 expected to emit? Select one: O i. recd O ii. yellow iiblue O iv. orange 2.2 2.0 1.8 1.2 0.8 0.6 0.4 0.2 x in SiGe,Sn-X What is the wave length in nm emitted by SiGeoSng? (Round you answer to the nearest whole number and omit the unit) Answer Forming covalent bonds Select one: O i. results in less stable state Oii lowers the potential energy of the bonding electrons O ili. increases the potential energy of the bonding electrons Breaking a bond -energy, while formation of a bond energy Select one: O i. releases, releases O ii. requires, requires O ili. releases, requires O iv, req uires, releases

Answer 1

1)

Increasing proportion of As in GaPAs LED reduces the band gap (energy, E).   

AsT oC

$E = \frac{hc}{\lambda }\Rightarrow E\propto \frac{1}{\lambda }$   from equation; reducing band gap increases wavelength.

So, $As_x \propto \lambda$

Decreasing As proportion from GaP_0.2As_0.8 to GaP_0.6As_0.4 will decrease wavelength.

So,  GaP_0.6As_0.4 will emit light of lower wavelength than green i.e. violet, indigo or blue.

GaP_0.6As_0.4 will emit blue light.

2)

SiGe_0.4Sn_0.6 : x=0.4 from given compound

From the graph, at x=0.4 , band gap = 1.8eV

(conversion: 1 eV = 1.6022e-19 J)

andgap = 1.8eV * 1.0122*10-19J le

E = 2.884*10^-19 J

$E = \frac{hc}{\lambda }$

$\Rightarrow \lambda = \frac{hc}{E}$

h = 6.626*10^-34 J.s ~ Planck's constant

c = 3*10⁸ m/s ~ speed of light

(6.626 10-34Js) (3*10sm/s)

6.89 * 10-1 m λ

λ 6.89 * 10-1 m 689nm 77n

3)

Bonds are formed between ions/compounds to achieve a stable state.

Potential energy(U) of covalent bonds is from the attractive force between ions/compounds

$U = -\frac{K}{r}$

where, U~potential energy of the covalent bond

K~constant

r ~distance between ions/compounds of covalent bond

When the ions/compounds are very far away from each other, r = infinity and U=0

When the ions/compounds come nearer to form covalent bond, r=finite and U= -ve

So, Forming covalent bonds lowers potential energy of bonding electrons.

4)

Breaking a bond releases energy.

breaking bonds requires separation the ions/compounds which increases the potential energy (energy released)

Formation of bond requires energy.

ions/compounds need to come closer for formation of bonds, which lowers potential (energy is required)