Advertisements
Advertisements
प्रश्न
Monochromatic radiation of wavelength 640.2 nm (1 nm = 10−9 m) from a neon lamp irradiates photosensitive material made of caesium on tungsten. The stopping voltage is measured to be 0.54 V. The source is replaced by an iron source and its 427.2 nm line irradiates the same photo-cell. Predict the new stopping voltage.
Advertisements
उत्तर
Wavelength of the monochromatic radiation, λ = 640.2 nm = 640.2 × 10−9 m
Stopping potential of the neon lamp, V0 = 0.54 V
Charge on an electron, e = 1.6 × 10−19 C
Planck’s constant, h = 6.6 × 10−34 Js
Let `phi_0` be the work function and ν be the frequency of emitted light.
We have the photo-energy relation from the photoelectric effect as:
eV0 = hv − `phi_0`
`phi_0 = "hc"/lambda - "eV"_0`
= `(6.6 xx 10^(-34) xx 3 xx 10^8)/(640.2 xx 10^(-9)) - 1.6 xx 10^(-19) xx 0.54`
= `3.093 xx 10^(-19) - 0.864 xx 10^(-19)`
= `2.229 xx 10^(-19) "J"`
`= (2.229 xx 10^(-19))/(1.6 xx 10^(-19))`
= 1.39 eV
Wavelength of the radiation emitted from an iron source, λ' = 427.2 nm
= 427.2 × 10−9 m
Let `"V"_0^"'"` be the new stopping potential. Hence, photo-energy is given as:
`"eV"_0^"'" = "hc"/(lambda"'") - phi_0`
= `(6.6 xx 10^(-34) xx 3 xx 10^(8))/(427.2 xx 10^(-9)) - 2.229 xx 10^(-19)`
= `4.63 xx 10^(-19) - 2.229 xx 10^(-19)`
= `2.401 xx 10^(-19) "J"`
`= (2.401 xx 10^(-19))/(1.6 xx 10^(-19))`
= 1.5 eV
Hence, the new stopping potential is 1.50 eV.
संबंधित प्रश्न
(a) Estimate the speed with which electrons emitted from a heated emitter of an evacuated tube impinge on the collector maintained at a potential difference of 500 V with respect to the emitter. Ignore the small initial speeds of the electrons. The specific charge of the electron, i.e., its e/m is given to be 1.76 × 1011 C kg−1.
(b) Use the same formula you employ in (a) to obtain electron speed for an collector potential of 10 MV. Do you see what is wrong? In what way is the formula to be modified?
The following graph shows the variation of photocurrent for a photosensitive metal :
(a) Identify the variable X on the horizontal axis.
(b) What does the point A on the horizontal axis represent?
(c) Draw this graph for three different values of frequencies of incident radiation v1, v2 and v3 (v1 > v2 > v3) for same intensity.
(d) Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I1 > I2 > I3) having same frequency.
Is it always true that for two sources of equal intensity, the number of photons emitted in a given time are equal?
It is found that yellow light does not eject photoelectrons from a metal. Is it advisable to try with orange light or with green light?
The equation E = pc is valid
If the frequency of light in a photoelectric experiment is doubled, the stopping potential will ______.
The collector plate in an experiment on photoelectric effect is kept vertically above the emitter plate. A light source is put on and a saturation photocurrent is recorded. An electric field is switched on that has a vertically downward direction.
A 100 W light bulb is placed at the centre of a spherical chamber of radius 20 cm. Assume that 60% of the energy supplied to the bulb is converted into light and that the surface of the chamber is perfectly absorbing. Find the pressure exerted by the light on the surface of the chamber.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
A sphere of radius 1.00 cm is placed in the path of a parallel beam of light of large aperture. The intensity of the light is 0.5 W cm−2. If the sphere completely absorbs the radiation falling on it, find the force exerted by the light beam on the sphere.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
Find the maximum magnitude of the linear momentum of a photoelectron emitted when a wavelength of 400 nm falls on a metal with work function 2.5 eV.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
The electric field associated with a monochromatic beam is 1.2 × 1015 times per second. Find the maximum kinetic energy of the photoelectrons when this light falls on a metal surface whose work function is 2.0 eV.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
A small piece of cesium metal (φ = 1.9 eV) is kept at a distance of 20 cm from a large metal plate with a charge density of 1.0 × 10−9 C m−2 on the surface facing the cesium piece. A monochromatic light of wavelength 400 nm is incident on the cesium piece. Find the minimum and maximum kinetic energy of the photoelectrons reaching the large metal plate. Neglect any change in electric field due to the small piece of cesium present.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
On the basis of the graphs shown in the figure, answer the following questions :
(a) Which physical parameter is kept constant for the three curves?
(b) Which is the highest frequency among v1, v2, and v3?
Define the term: stopping potential in the photoelectric effect.
In photoelectric effect the photo current ______.
Do all the electrons that absorb a photon come out as photoelectrons?
Consider a 20 W bulb emitting light of wavelength 5000 Å and shining on a metal surface kept at a distance 2 m. Assume that the metal surface has work function of 2 eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 Å.
- Estimate no. of photons emitted by the bulb per second. [Assume no other losses]
- Will there be photoelectric emission?
- How much time would be required by the atomic disk to receive energy equal to work function (2 eV)?
- How many photons would atomic disk receive within time duration calculated in (iii) above?
- Can you explain how photoelectric effect was observed instantaneously?
The work function for a metal surface is 4.14 eV. The threshold wavelength for this metal surface is ______.
If photons of ultraviolet light of energy 12 eV are incident on a metal surface of work function of 4 eV, then the stopping potential (in eV) will be :
