Average force exerted on a non-reflecting surface at normal incidence is . If 360 is the light energy flux during span of 1 hour 30 minutes, Then the area of the surface is [2024]
(1)
An object is placed in a medium of refractive index 3. An electromagnetic wave of intensity falls normally on the object and it is absorbed completely. The radiation pressure on the object would be (speed of light in free space ) [2024]
(3)
Two sources of light emit with a power of 200 W. The ratio of the number of photons of visible light emitted by each source having wavelengths 300 nm and 500 nm respectively, will be [2024]
3 : 5
1 : 5
5 : 3
1 : 3
(1)
Monochromatic light of frequency is produced by a laser. The power emitted is . How many photons per second, on an average, are emitted by the source? [2024]
(Given Js)
(3)
In the Franck-Hertz experiment, the first dip in the current-voltage graph for hydrogen is observed at 10.2 V. The wavelength of light emitted by the hydrogen atom when excited to the first excitation level is ___ nm.
(Given ) [2024]
(122)
If the total energy transferred to a surface in time is , then the magnitude of the total momentum delivered to this surface for complete absorption will be [2024]
(2)
Energy transferred in time
For complete absorption
So
The radiation pressure exerted by a 450 W light source on a perfectly reflecting surface placed 2 m away from it, is [2025]
0
(3)
Where = intensity at surface
c = Speed of light
A small mirror of mass m is suspended by a massless thread of length . Then the small angle through which the thread will be deflected when a short pulse of laser of energy E falls normal on the mirror (c = speed of light in vacuum and g = acceleration due to gravity) [2025]
(4)
Force due to beam assuming complete reflection
; P is power
So change in momentum of mirror.
... (i)
Now using work energy theorem
as is small
from eq. (i)
The ratio of the power of a light source to that the light source is 2. is emitting photons per second at 600 nm. If the wavelength of the source is 300 nm, then the number of photons per second emitted by is _____ . [2025]
(5)
Since power emitted by a source is given as
Substituting the given values