Optical Properties - Properties and Applications of Materials - Engineering Sciences Previous Year Questions

1

2012 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2012

Of the following materials, which is the most suitable for an LED emitting at around 380 nm?

A

Direct bandgap material with a small bandgap

B

Indirect bandgap material with a large bandgap

C

Direct bandgap material with a large bandgap

D

Indirect bandgap material with a small bandgap

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2

2013 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2013

The band gap of a semiconducting material used to make an LED is 1.43 eV. What will be the minimum wavelength of the radiation emitted by this LED, in μm?

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3

2015 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2015

What is the thickness (in μm) of a germanium crystal layer that would be required for absorbing 80% of the incident radiation whose wavelength is 1.3 μm? The absorption coefficient (α) of germanium at 1.3 μm is 3.3 x 10⁵ m⁻¹.

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4

2016 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2016

Defect-free single crystal alumina (sapphire) is

A

opaque and white.

B

transparent.

C

translucent.

D

opaque and black.

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5

2016 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2016

A direct bandgap semiconductor has a bandgap of 1.8 eV. The threshold value of the wavelength BELOW which this material will absorb radiation is __________ Å.
(Given: Planck's constant, \( h = 6.626 \times 10^{-34} \) J s, the charge of an electron, \( e = 1.6 \times 10^{-19} \) C, and speed of light, \( c = 3 \times 10^8 \) m s\(^{-1}\))

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6

2017 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2017

An inorganic material that is transparent under solar light appears coloured when doped with transition metal ions. The possible reason(s) for the colour is/are
(i) The electronic energy levels of the host material changes significantly by doping
(ii) The doped element selectively absorbs certain wavelength of light other than the perceived colour
(iii) The doped element emits radiation of specific wavelength

Which of the above statement(s) is/are true?

A

Only (i)

B

Both (i) and (ii)

C

Both (i) and (iii)

D

Both (ii) and (iii)

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7

2019 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2019

The maximum wavelength of radiation to which Germanium (Ge) is opaque will be
(Given: energy gap of Ge = 0.67 eV, Planck’s constant h = 6.63 × 10⁻³⁴ J.s, velocity of light c = 3×10⁸ m s⁻¹ and 1 eV = 1.6×10⁻¹⁹ J)

A

0.8 μm

B

1.8 μm

C

2.8 μm

D

4.8 μm

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8

2020 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2020

The schematic diagram shows the light of intensity I₀ incident on a material (shaded grey) of thickness, x, which has an absorption coefficient, α and reflectance, R. The intensity of transmitted light is I. The reflection of light (of a particular wavelength) occurs at both the surfaces (surfaces indicated in the diagram). The transmittance is estimated to be ______ (round-off to three decimal places).
Given that for the wavelength used, α = 10³ m^-1 and R = 0.05.

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9

2022 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2022

A new glass material is developed to minimize the transmission of the light through the window with glass panel of thickness 5 mm. The refractive index of the glass material is 1.5 and the absorption coefficient can be changed from 0.3 cm⁻¹ to 1 cm⁻¹. In the given range of absorption coefficients, the ratio of the maximum to the minimum fraction of the light coming out of the other side of the glass panel is ______. (Round off to two decimal places)

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10

2023 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2023

The band gap of a semiconducting material is ~ 2 eV. Which one of the following absorption (A) vs. energy (in eV) curves is correct?

A

B

C

D

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11

2024 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2024

In a typical light emitting diode (LED), which of the following type(s) of materials is/are used?

A

Indirect bandgap semiconductor with transition metal impurities

B

Direct bandgap semiconductor

C

Indirect bandgap semiconductor with isoelectronic impurities

D

Indirect bandgap semiconductor without any impurity

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12

2024 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2024

Biaxially oriented poly(propylene) exhibits high clarity because layering of the crystalline structures

A

decreases the variation in refractive index across the film thickness

B

decreases the amount of light scattering

C

increases the variation in refractive index across the film thickness

D

increases the amount of light scattering

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13

2025 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2025

Which of the following phenomenon/phenomena contribute to intensity loss of electromagnetic radiation during transmission through a medium?

A

Electronic absorption

B

Rayleigh scattering

C

Photon – phonon interaction

D

Stimulated emission

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14

2025 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2025

A GaP-GaAs semiconductor LED display has a band gap of 1.9 eV. The wavelength of emitted light in μm is (rounded off to two decimal places) ______
Given: Planck’s constant = 6.63 × 10⁻³⁴ J s
Velocity of light = 3 × 10⁸ m s⁻¹
1 eV = 1.6 × 10⁻¹⁹ J

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15

2026 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2026

The band gap of a material is \(E_g\) and the energy of an incident photon is \(E_p\). Optical absorption will occur in this material if,

A

\(E_g < E_p\)

B

\(E_g > E_p\)

C

Electron-electron recombination occurs

D

Electron-hole recombination occurs

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16

2026 · Engineering Sciences · Properties and Applications of Materials · Optical Properties

Engineering Sciences (XE) 2026

The luminous efficacy of an electric light bulb is measured in which one of the following units?

A

lumen W^-1

B

lumen W^-1 h^-1

C

lumen m^-2

D

candela W^-1

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