Electromagnetic radiation with a wavelength of 471 nm appears as blue light to the human eye.The energy of one photon of this light is 4.22 × $10 ^ { - 19 }$ J.Thus,a laser that emits $1.3 \times 10 ^ { - 2 } \mathrm {~J}$ of energy in a pulse of light at this wavelength produces ________ photons in each pulse. A)1.5 × $10 ^ { 19 }$ B)1.2 × 10^-23 C)3.2 × $10 ^ { - 17 }$ D)3.1 × $10 ^ { 16 }$ E)6.5 × $10 ^ { 13 }$

Question

Quizplus · Accepted Answer

The energy of one photon is given as:
$E = hc/\lambda$
where $h$ is Planck's constant, $c$ is the speed of light and $\lambda$ is the wavelength.
Substituting the given values,
$4.22 × 10^{-19} J = h \cdot 3 \cdot 10^8 m/s / (471 \cdot 10^{-9} m) $
Solving for $h$ gives us Planck's constant as $6.63 \cdot 10^{-34} J \cdot s$.
Now, the number of photons emitted in each pulse can be calculated as:
$1.3 \cdot 10^{-2}J / (4.22 \cdot 10^{-19}J/photon) = 3.08 \cdot 10^{16}$ photons/pulse.
Therefore, the best choice is Option D.

Electromagnetic Radiation with a Wavelength of 471 Nm Appears as Blue