Advertisements
Advertisements
प्रश्न
A beam of white light is incident normally on a plane surface absorbing 70% of the light and reflecting the rest. If the incident beam carries 10 W of power, find the force exerted by it on the surface.
(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)
Advertisements
उत्तर
Power of the incident beam, P = 10 watt
Relation between wavelength (λ) and momentum (p):
`λ = h/p` ,
where h is Planck's constant
⇒ `p = h/λ`
On dividing both sides by t , we get :
`p/t = h/(λt)` ...(1)
Energy,
`E = (hc)/λ`
⇒ `E/t = (hc)/(λt)`
Let P be the power . Then,
`P = E/t = (hc)/(λt)`
`P = (pc)/t ................["Using equation (1)"]`
⇒` p/c = p/t`
Force ,
`F = p/t = p/c` `("Since F" = "Momentum"/"Time")`
`"Force, F" = 7/10 " (absorted)" + 2 xx 3/10 ("reflected")`
`F = 7/10 xx P/c + 2 xx 3/10 xx P/c`
`F = 7/10 xx 10/(3 xx 10^8) + 2 xx 3/10 xx 10/(3 xx 10^8)`
`F = 13/3 xx 10^-8 = 4.33 xx 10^-8 "N"`
APPEARS IN
संबंधित प्रश्न
Define the term 'intensity of radiation' in terms of photon picture of light.
The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy of photoelectrons emitted?
(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?
Can a photon be deflected by an electric field? Or by a magnetic field?
If an electron has a wavelength, does it also have a colour?
If the wavelength of light in an experiment on photoelectric effect is doubled,
(a) photoelectric emission will not take place
(b) photoelectric emission may or may not take place
(c) the stopping potential will increase
(d) the stopping potential will decrease
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.
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.
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.
In the case of photoelectric effect experiment, explain the following facts, giving reasons.
The photoelectric current increases with increase of intensity of incident light.
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.
The graph shows the variation of photocurrent for a photosensitive metal
- What does X and A on the horizontal axis represent?
- Draw this graph for three different values of frequencies of incident radiation ʋ1, ʋ2 and ʋ3 (ʋ3 > ʋ2 > ʋ1) for the same intensity.
- Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I3 > I2 > I1) having the same frequency.
Why it is the frequency and not the intensity of the light source that determines whether the emission of photoelectrons will occur or not? Explain.
Which radiation does quartz window W especially allow to enter the tube?
Which plate is kept illuminated by monochromatic radiation?
Which observation was one of the major difficulties for classical wave theory?
