Advertisements
Advertisements
प्रश्न
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.
Advertisements
उत्तर
Work function (or threshold energy) (W0): The minimum energy of incident radiation required to eject the electrons from the metallic surface is defined as the work function of that surface.
W0 = hv0 = `(hc)/λ_0` Joules; v0 = Threshold frequency; λ0 = Threshold wavelength
Work function in electron volt, W0(eV) = `(hc)/(eλ_0) = 12375/(λ_0(Å))`
Einstein's photoelectric equation is E = W0 + Kmax
Maximum energy = `hv - phi`
According to the problem for the first condition wavelength of light λ = 600 nm and for the second condition, the wavelength of light λ' = 400 nm
Also, the maximum kinetic energy for the second condition is equal to twice the kinetic energy in the first condition.
i.e., K'max = 2Kmax
then K'max = `(hc)/λ - phi`
⇒ 2Kmax = `(hc)/λ^' - phi`
⇒ `2(1230/600 - phi) = (1230/400 - phi)` ......[∵ hc = 1240 eV nm]
⇒ `phi = 1230/1230` = 1.02 eV
APPEARS IN
संबंधित प्रश्न
Should the energy of a photon be called its kinetic energy or its internal energy?
In an experiment on photoelectric effect, a photon is incident on an electron from one direction and the photoelectron is emitted almost in the opposite direction. Does this violate the principle of conservation of momentum?
The threshold wavelength of a metal is λ0. Light of wavelength slightly less than λ0 is incident on an insulated plate made of this metal. It is found that photoelectrons are emitted for some time and after that the emission stops. Explain.
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 totally reflecting, small plane mirror placed horizontally faces a parallel beam of light, as shown in the figure. The mass of the mirror is 20 g. Assume that there is no absorption in the lens and that 30% of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror.
(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.
Show that it is not possible for a photon to be completely absorbed by a free electron.
The work function of a photoelectric material is 4.0 eV. (a) What is the threshold wavelength? (b) Find the wavelength of light for which the stopping potential is 2.5 V.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
In an experiment on photoelectric effect, the stopping potential is measured for monochromatic light beams corresponding to different wavelengths. The data collected are as follows:-
Wavelength (nm): 350 400 450 500 550
Stopping potential (V): 1.45 1.00 0.66 0.38 0.16
Plot the stopping potential against inverse of wavelength (1/λ) on a graph paper and find (a) Planck's constant (b) the work function of the emitter and (c) the threshold wavelength.
(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 light wave is given by `E = E_0 sin [(1.57 xx 10^7 "m"^-1)(x - ct)]`. Find the stopping potential when this light is used in an experiment on photoelectric effect with the emitter having work function 1.9 eV.
Define the term: threshold frequency
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?
In photoelectric effect the photo current ______.
The difference between threshold wavelengths for two metal surfaces A and B having work function ΦA = 9 eV and ΦB = 4.5 eV in nm is ______.
(Given, hc = 1242 eV nm)
What is studied when light falls on a metal surface?
Which apparatus applies a potential difference between the plates?
What is used to change light frequency and study its effect on emission and electron energy?
How quickly does photoelectric emission occur when suitable radiation falls on the metal surface?
Which observation was one of the major difficulties for classical wave theory?
