Download App

Question Bank [ 2022 ] — Physics STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsQuestion Bank [ 2022 ]1 Mark
MCQ
A LED emits visible white light when its ______  
  • A
    junction is reversed-biased.
  • B
    depletion layer widens.
  • ✓
    holes and electrons recombine.
  • D
    junction becomes hot.
✓

Answer

Correct option: C.
holes and electrons recombine.
A LED emits visible white light when its holes and electrons recombine.

Explanation:

LED is a semi-conductor source of light which emits light when current flows through it. When electrons in semiconductors recombine with electron holes, releasing energy, in the form of photons.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from Question Bank [ 2022 ]→Question Bank [ 2022 ] — all question types→Physics STD 12 Science question papers→Maharashtra Board STD 12 Science question papers→Maharashtra Board question paper generator→

Similar questions

If the frequency of the input voltage is $50 Hz$, applied to a (a) half wave rectifier and (b) full wave rectifier. The output frequency in both cases is respectively
→
When one end of the capillary is dipped in water, the height of water column is $h$. The upward force of 105 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of the capillary is (Surface tension of water $=7 \times 10^{-2} N / m$ )
→
If $I_0$ is the intensity of the principal maximum in the single slit diffraction pattern, then what will be the intensity when the slit width is doubled?
→
In a serics LCR circuit the phase difference between the voltage and the current is 45". Then the power factor will be _________.
→
The surface tension of a liquid at critical temperature is ______ 
→
Two closely-spaced distant stars are just resolved when seen through a telescope with an objective lens of diameter $D$ and focal length $f$. The separation between their images is given by.
→
If $\lambda$ is the wavelength of light used in Young's double-slit experiment, the path difference for a phase difference of $11 \pi$ rad is
→
A particle executes SHM of type $x=A \sin \omega t$. It takes time $t_1$ from $x=0$ to $x=\frac{A}{2}$ and $t_2$ from $x=\frac{A}{2}$ to $x=A$. The ratio $t_1 ; t_2$ will be
→
A tuning fork gives 1 beat in 2 seconds with a timing fork of frequency $341.3 Hz$. If the beat: frequency decreases when the first fork is filed a little, its original frequency was
→
A hydraulic lift is designed to lift heavy objects of a maximum mass of $2000 \ kg$ . The area of the cross-section of the piston carrying the load is $2.25 \times 10^{-2} m^2$. What is the maximum pressure the piston would have to bear?
→