Question

What is the energy of a photon of light of wavelength of $575nm$ ?

Answer 1

Hint : To solve the given question, we should have information about frequency, wavelength, speed of light and energy of photons.
Frequency is known as the number of oscillations of waves per unit time. It is expressed in $Hertz$ . Wavelength is the distance between two consecutive crests and troughs. It is mainly expressed in $m$ . Speed of light basically is the speed of light particles travelling in vacuum. Its value is $3 \times 10^8 msec^{ -1 }$ .
Energy of a photon is the energy carried by the photon which is transferred to a metallic surface if the photon strikes it.
The only formula used is :
$E = \dfrac{hc }{ \lambda }$
Where,
$E \rightarrow$ Energy of photon
$h \rightarrow$ Plank’s Constant
$\lambda \rightarrow$ Wavelength
$c \rightarrow$ Speed of light.

Complete Step By Step Answer:
Step-1 :
We have given the speed of light as $3 \times 10^8 msec^{ -1 }$ and the wavelength of photon as $575 nm$ , which can be further equal to $575 \times 10^{ -9 }m$ . The value of Planck's constant is $6.6 \times 10^{ -34 } Js$ .
Step-2 :
Using the given above formula, we have ;
$E = \dfrac{ hc }{ \lambda }$
$= \dfrac{ 6.6 \times 10^{ -34 } 3 \times 10^8 }{ 575 \times 10^{ -9 }}$
$E = 3.46 \times 10^{ -19 }J$

Note :
Remember to calculate the energy in Joule by having other parameters in $SI$ unit. To convert $J$ to $eV$ , divide it by $1.6 \times 10^{ -19 }$ as we know that $1eV = 1.6 \times 10^ { -19 }J$ .Rest mass of photon is zero i.e. photon can never be at rest. Under suitable conditions, photons show the phenomenon of diffraction and polarization. Photons are electrically neutral because they do not get deflected by the presence of electricity in the magnetic field.