Monochromatic light of frequency `6xx10^(14)Hz` is produced by a laser. The power emitted is `2xx10^(-3)` W.
The number of photons emitted per second is
`("Given h"=6.63xx10^(-34)Js)`

Options

A. `2xx10^(15)`
B. `3xx10^(15)`
C. `4xx10^(15)`
D. `5xx10^(15)`

Explanation

To solve the problem of finding the number of photons emitted per second by a laser emitting monochromatic light, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Frequency of light, \( \nu = 6 \times 10^{14} \, \text{Hz} \)
- Power emitted, \( P = 2 \times 10^{-3} \, \text{W} \)
- Planck's constant, \( h = 6.63 \times 10^{-34} \, \text{Js} \)

2. **Calculate the Energy of One Photon:**
The energy \( E \) of one photon can be calculated using the formula:
\[ E = h \cdot \nu \]
Substituting the values:
\[ E = (6.63 \times 10^{-34} \, \text{Js}) \cdot (6 \times 10^{14} \, \text{Hz}) \]
\[ E = 3.978 \times 10^{-19} \, \text{J} \]
(We can round this to \( E \approx 3.98 \times 10^{-19} \, \text{J} \))

3. **Relate Power to Number of Photons:**
The power emitted can also be expressed in terms of the number of photons emitted per second \( n \) and the energy of each photon:
\[ P = n \cdot E \]
Rearranging this gives:
\[ n = \frac{P}{E} \]

4. **Substitute the Values to Find \( n \):**
Now, substituting the values of power and energy:
\[ n = \frac{2 \times 10^{-3} \, \text{W}}{3.98 \times 10^{-19} \, \text{J}} \]
\[ n \approx 5.013 \times 10^{15} \, \text{photons} \]
(This can be rounded to \( n \approx 5 \times 10^{15} \, \text{photons} \))

5. **Final Result:**
The number of photons emitted per second is approximately:
\[ n \approx 5 \times 10^{15} \, \text{photons} \]