# Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 13

Q: 46. Nitrogen laser produces a radiation at a wavelength of 337.1 nm. If the number of photons emitted is calculate the power of this laser.

Answer:

Power of laser = Energy with which it emits photons

Power

Where,

N = number of photons emitted

h = Planck’s constant

c = velocity of radiation

Wavelength of radiation

Substituting the values in the given expression of Energy (E):

Hence, the power of the laser is

Q: 47. Neon gas is generally used in the sign boards. If it emits strongly at 616 nm, calculate

(a) The frequency of emission

(b) Distance traveled by this radiation in 30 s

(c) Energy of quantum and

(d) Number of quanta present if it produces 2 J of energy.

Answer:

Wavelength of radiation emitted = 616 nm =

(a) Frequency of emission (v)

Where,

C = velocity of radiation

Wavelength of radiation

Substituting the values in the given expression of (v):

Frequency of emission =

Velocity of radiation,

Distance travelled by this radiation in 30 s

(c) Energy of quantum (E) =

Energy of quantum (E)

(d)Energy of one photon (quantum)

Therefore, of energy is present in quantum.

Number of quanta in 2 J of energy

Q: 48. In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of from the radiations of 600 nm, calculate the number of photons received by the detector.

Answer:

From the expression of energy of one photon (E),

Where,

h = Planck’s constant

c = Velocity of radiation

Substituting the value in the given expression of E:

E

E=

Energy of one photon

Number of photons received with energy

(Approx 10)