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.
APPEARS IN
संबंधित प्रश्न
Define the term 'intensity of radiation' in terms of photon picture of light.
Ultraviolet light of wavelength 2271 Å from a 100 W mercury source irradiates a photo-cell made of molybdenum metal. If the stopping potential is −1.3 V, estimate the work function of the metal. How would the photo-cell respond to a high intensity (∼105 W m−2) red light of wavelength 6328 Å produced by a He-Ne laser?
Is it always true that for two sources of equal intensity, the number of photons emitted in a given time are equal?
A hot body is placed in a closed room maintained at a lower temperature. Is the number of photons in the room increasing?
Should the energy of a photon be called its kinetic energy or its internal energy?
If an electron has a wavelength, does it also have a colour?
Two photons of
The work function of a metal is hv0. Light of frequency v falls on this metal. Photoelectric effect will take place only if
A point source of light is used in a photoelectric effect. If the source is removed farther from the emitting metal, the stopping potential
A point source causes photoelectric effect from a small metal plate. Which of the following curves may represent the saturation photocurrent as a function of the distance between the source and the metal?
An atom absorbs a photon of wavelength 500 nm and emits another photon of wavelength 700 nm. Find the net energy absorbed by the atom in the process.
(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, Show that the force on the sphere due to the light falling on it is the same even if the sphere is not perfectly absorbing.
When a metal plate is exposed to a monochromatic beam of light of wavelength 400 nm, a negative potential of 1.1 V is needed to stop the photo current. Find the threshold wavelength for the metal.
(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 figure is the plot of stopping potential versus the frequency of the light used in an experiment on photoelectric effect. Find (a) the ratio h/e and (b) the work function.
Answer the following question.
Plot a graph of photocurrent versus anode potential for radiation of frequency ν and intensities I1 and I2 (I1 < I2).
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 terms "stopping potential' and 'threshold frequency' in relation to the photoelectric effect. How does one determine these physical quantities using Einstein's equation?
Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. Find the work function in eV.
Read the following paragraph and answer the questions.
| The figure shows the variation of photoelectric current measured in a photocell circuit as a function of the potential difference between the plates of the photocell when light beams A, B, C and D of different wavelengths are incident on the photocell. Examine the given figure and answer the following questions: |
- Which light beam has the highest frequency and why?
- Which light beam has the longest wavelength and why?
- Which light beam ejects photoelectrons with maximum momentum and why?
A metallic plate exposed to white light emits electrons. For which of the following colours of light, the stopping potential will be maximum?
