What Determines the Intensity in the Photon Picture of Light? - Physics


When monochromatic light is incident on a surface separating two media, the reflected and refracted light both have the same frequency as the incident frequency.



Frequency and wavelength of light are related as


where v is the velocity of light. As the wave travels from one medium to another, the wavelength of light changes changing the speed of light with it. The frequency remains constant. 

Concept: Refraction of Monochromatic Light
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2015-2016 (March) All India Set 2 C


Monochromatic light of frequency 6.0 × 1014 Hz is produced by a laser. The power emitted is 2.0 × 10−3 W. Estimate the number of photons emitted per second on an average by the source

When light travels from a rarer to a denser medium, the speed decreases. Does this decrease in speed imply a reduction in the energy carried by the wave?

A monochromatic ray of light falls on a regular prism. What is the relation between the angle of incidence and angle of emergence in the case of minimum deviation?

State the essential conditions for diffraction of light ?

Monochromatic light of frequency 5.0 × 1014 Hz is produced by a laser. The power emitted is 3.0 × 10–3 W. Estimate the number of photons emitted per second on an average by the source ?

Obtain the conditions for the bright and dark fringes in diffraction pattern due to a single narrow slit illuminated by a monochromatic source.

Explain clearly why the secondary maxima go on becoming weaker with increasing.

Which of the following sources provides the best monochromatic light?

The following figure shows three equidistant slits being illuminated by a monochromatic parallel beam of light. Let \[B P_0  - A P_0  = \lambda/3\text{ and }D >  > \lambda.\] (a) Show that in this case \[d = \sqrt{2\lambda D/3}.\] (b) Show that the intensity at P0 is three times the intensity due to any of the three slits individually.

Consider the situation shown in the figure. The two slits S1 and S2 placed symmetrically around the central line are illuminated by a monochromatic light of wavelength λ. The separation between the slits is d. The light transmitted by the slits falls on a screen ∑1placed at a distance D from the slits. The slit S3 is at the central line and the slit S4 is at a distance z from S3. Another screen ∑2 is placed a further distance D away from ∑1.Find the ratio of the maximum to minimum intensity observed on ∑2 if z is equal to

(a) \[z = \frac{\lambda D}{2d}\]

(b) \[\frac{\lambda D}{d}\]

(c) \[\frac{\lambda D}{4d}\]

"Monochromatic light should be used to produce pure spectrum". Comment on this statement.

Can the interference pattern be produced by two independent monochromatic sources of light? Explain.

Monochromatic light of wavelength 650 nm falls normally on a slit of width 1.3 x 10-4 cm and the resulting Fraunhofer diffraction is obtained on a screen. Find the angular width of the . central maxima.

Find the angle of incidence at which a ray of monochromatic light should be incident on the first surface AB of a regular glass prism ABC so that the emergent ray grazes the adjacent surface AC. (Refractive Index of glass = 1 .56)

Monochromatic fight of wavelength 198 nm is incident on the surface of a metallic cathode whose work function is 2.5 eV How much potential difference must be applied between the cathode and the anode of a photocell to just stop the photocurrent from flowing? 

Answer the following question.
In the diffraction due to a single slit experiment, the aperture of the slit is 3 mm. If monochromatic light of wavelength 620 nm is incident normally on the slit, calculate the separation between the first order minima and the 3rd order maxima on one side of the screen. The distance between the slit and the screen is 1.5 m.

(a) Can the interference pattern be produced by two independent monochromatic sources of light? Explain.
(b) The intensity at the central maximum (O) in Young's double-slit experimental set-up shown in the figure is IO. If the distance OP equals one-third of the fringe width of the pattern, show that the intensity at point P, would `"I"_°/4`

(c) In Young's double-slit experiment, the slits are separated by 0⋅5 mm and the screen is placed 1⋅0 m away from the slit. It is found that the 5th bright fringe is at a distance of 4⋅13 mm from the 2nd dark fringe. Find the wavelength of light used.

A monochromatic ray of light falls on a regular prism under minimum deviation condition. What is the relation between angle of incidence and angle of emergence?

For constructive interference to take place between two monochromatic light waves of wavelength λ, the path difference should be ______.

Assertion(A): The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.

Reason(R): The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

Monochromatic light of wavelength 600 nm is incident from the air on a water surface. The refractive index of water is 1.33. Find the

  1. wavelength,
  2. frequency and
  3. speed, of reflected and refracted light.

Monochromatic light of wavelength 396 nm is incident on the surface of a metal whose work function is 1.125 eV. Calculate:

  1. the energy of an incident photon in eV.
  2. the maximum kinetic energy of photoelectrons in eV.


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