Light Emitting Diode

Q.

State the four laws of photoelectric emissions.

Q. The electric field intensity produced by the radiation coming from a $100\text{W}$ bulb at a distance of $3\text{m}$ is $E$. The electric filed intensity produced by the radiation coming from $60\text{W}$ at the same distance is $\sqrt{\frac{x}{5}}E$. Where the value of $x$ is .

Q. Find the amplitude of the electric field in a parallel beam of light of intensity $2.0{\text{Wm}}^{-2}$.

1. $15.5\text{N/C}$
2. $38.8\text{N/C}$
3. $40.3\text{N/C}$
4. $53.6\text{N/C}$

Q. In a PN-junction diode not connected to any circuit

1. The potential is the same everywhere
2. The P-type is a higher potential than the N-type side
3. There is an electric field at the junction directed from the N- type side to the P- type side
4. There is an electric field at the junction directed from the P-type side to the N-type side

Q. LED is constructed from $Ga-As-P$ semiconducting material. The energy gap of this LED is $1.9\text{eV}$. Calculate the wavelength of light emitted and its colour.
$[h=6.63\times {10}^{34}\text{J s}\text{and}c=3\times {10}^8{\text{ms}}^{-1}]$

1. $654\text{nm}$ and red colour
2. $1046\text{nm}$ and blue colour
3. $1046\text{nm}$ and red colour
4. $654\text{nm}$ and orange colour

Q.

The colour of light emitted by LED depends on:

1. Its reverse bias

2. The amount of forward current

3. Its forward bias

4. Type of semiconductor material

Q. A 10 m long potentiometer wire is connected to a battery having a steady voltage a leclanche cell is obtained at 4 m length of wire if the length is kept same but its cross section is doubled the null point will be obtained at

Q. what is electric flux through a ring?

Q. How many 1 micro farad capacitors must be connected in parallel to store a charge of 1C with a potential 110 V across the capacitors

Q. given that a photon of light of wavelength 10000Ang has energy 1.23eV. now when the light ofintensity Io and wavelength 5000Ang falls on a photo cell the saturation current and stopping potential are 0.40micro ampere and 1.36V respectively. the work function

Q. the sodium yellow doublet have wavelengths 5890 angstrom and λ angstrom and resolving power of a grating to resolve these lines is 982 then value of λ is

Q. 93.Given that a photon of light of wavelength 10000 angstorm has energy 1.23 eV .Now when light of intensity I and wavelength 5000 angstorm falls on a photo cell the saturation current and stopping potential are 0.40 micro Ampere and 1.36 V respectively. THE workfunction is

Q. Two separate monochromatic light beams $\text{A}$ and $\text{B}$ of the same intensity (energy per unit area per unit time) are falling normally on a unit area of a metallic surface. Their wavelength is ${\lambda }_A$ and ${\lambda }_B$ respectively. Assuming that all the incident light is used in ejecting the photoelectrons, the ratio of the number of photoelectrons ejected by beam $\text{A}$ to that beam $\text{B}$ is-

1. $\left(\frac{{\lambda }_A}{{\lambda }_B}\right)$
2. $\left(\frac{{\lambda }_B}{{\lambda }_A}\right)$
3. ${\left(\frac{{\lambda }_A}{{\lambda }_B}\right)}^2$
4. ${\left(\frac{{\lambda }_B}{{\lambda }_A}\right)}^2$

Q. Light of frequency $f$ is incident on a photosensitive surface of threshold frequency $\frac{f}{2}$. The energy of the fastest photoelectron is found to be equal to $K$. If the frequency of the incident radiation is doubled, then the energy of the fastest electron will be

1. $3K$
2. $2K$
3. $K$
4. $\frac{K}{2}$

Q. The threshold wavelength of a photo sensitive metal is 275 nm. Calculate the maximum velocity of the photo electrons ejected when light of 180nm incident on it.

Q. To get steady DC output from the pulsating voltage, one can use -

1. Both capacitor or inductor
2. Inductor
3. Capacitor
4. None of these

Q. The intensity of X-rays of wavelength 0.5 Angstrom reduces to one fourth on passing through 3.5 mm thickness of a metal foil. The coefficient of absorption of metal will be- (1) 0.2 mm^-1 (2) 0.3 mm^-1 (3) 0.4 mm^-1 (4) 0.5 mm^-1

Q. An RC circuit connected with a battery of emf E volts. At 1 time constant the charge on the capacitor is,

1. 0.63 EC
2. 0.37 EC
3. 0.5 EC
4. EC

Q. distinguish between conductors insulators and semiconductors on the basis of Band theory

Q.

A red LED emits light at $0.1Watt$ uniformly around it. The amplitude of the electric field of the light at a distance $1m$ from the diode is

Q.

What is the full form of LED, LCD, MCB, USB, CFL, CFC?

Q. A beam of light consisting of two wavelengths $420\text{nm}$ and $540\text{nm}$ falls on two metals $1$ and $2$ of work functions $4.0\text{eV}$ and $2.5\text{eV}$ respectively. If the intensities of the two wavelengths are equal, which of the graphs shown in figure represents the variation of photoelectric current $\left(i\right)$ with voltage $\left(V\right)$ is correct?
[Take $hc=1240\text{eV (nm)}$ ]

1. 
2. 
3. 
4. 

Q. In which region, the transistor as a switch is OFF?

1. Cut-off
2. Saturation
3. Active
4. None of these

Q. H Alpha line of Balmer series 6500 angstroms the wavelength of h GaMa is?

Q.

How do you know when a diode is bad?

Q. A laser beam has intensity $2.5\times {10}^{14}{\text{Wm}}^{-2}$. The amplitudes of electric and magnetic fields in the beam are,

1. $1.44\times {10}^8\text{N/C},4.34\text{T}$
2. $4.34\text{N/C},1.44\text{T}$
3. $4.34\times {10}^8\text{N/C},1.44\text{T}$
4. $1.25\times {10}^8\text{N/C},4.34\text{T}$

Q. Show that current lags voltage by 90° in a.c. containing an ideal inductor

Q. the work functionof a surface of a photosensitive material is 6.2eV. The wavelength of the incident radiationfor which the stopping potential is 5

Q. 86.Work function of Zn is 3.74eV. If the sphere of Zn is illuminated by the X rays of wavelength 12angstroms, find the maximum potential production on the sphere , h =6.625\ast10^{-34} Js

Q. for a monochromatic radiation incident on a photosensitive surface why do all photoelectrons not come out with the same energy??