A laser pulse with wavelength 532 nm contains 3.85 mJ of energy. How many photons are in the las

A laser pulse with wavelength 532 nm contains 3.85 mJ of...

Key Concepts

Photon Energy and Quantization

Light is quantized, meaning it is made of discrete packets called photons. Each photon has an energy that is determined by its wavelength through the relationship E = hc/?, where h is Planck’s constant and c is the speed of light. This concept underscores that energy is not continuous but comes in steps, with each photon carrying a specific quantum of energy.

Planck's Equation and Fundamental Constants

Planck's equation (E = hc/?) is central to quantum physics as it links the wave properties of light (wavelength) with its particle properties (energy per photon). The use of Planck’s constant and the speed of light in this equation reflects the essential role these fundamental constants play in connecting the realms of classical and quantum physics.

Unit Conversion

Accurate physical calculations require consistent units. Converting measurements such as energy from millijoules to joules and wavelength from nanometers to meters is a crucial step in applying physical formulas correctly. This ensures that all quantities are in their proper SI units, allowing for the direct and accurate application of equations.

Photon Counting through Energy Division

Once the energy per photon is calculated, the total number of photons in a light pulse can be determined by dividing the total pulse energy by the energy of one photon. This method of photon counting is a practical application of the quantization of energy, illustrating how macroscopic energy values can be related to the count of microscopic energy carriers.

Transcript

00:01 How's it going people? for this question, we're supposed to find the number of photons or light particles in the laser pulse, and we're given a wavelength in nanometers and energy in milletrols.

00:14 So in this case, we want to find the number of photons.

00:18 We're given some property of the light particle, and we're given the total energies.

00:22 So the number of photons, number of light particles will equal to the total energy level, which we are given in millerjoues, divided by energy per photon.

00:42 And thus we can calculate the number of photons in this laser powers.

00:47 And we're given, we know the formula for energy has energy equals to plants constant times the frequency of the light.

00:56 Right, the radiation.

00:59 But here we don't have the frequency, but we do have the wavelength, and we know that there's another relationship, c equals to lambda times frequency that relates lambda and new, which is the frequency together.

01:13 And now we can sub in the frequency here.

01:20 We note new equals to c over lambda, and we sub in the expression here.

01:27 So we're going to have e equals time, e equals to planx constant times c, which is the constant for speed of light in a vacuum, divided by lambda.

01:36 This gives us the energy per photon.

01:42 And now let's take a look.

01:44 We know the total energy level, right? we know the total energy level.

01:52 We know the energy per photon from the equation here.

01:58 And now we just have to plug in the formula.

02:01 So we have total energy.

02:05 Total energy we have 3 .85 millilitules.

02:11 I want to do a quick unit conversion.

02:14 We have a thousand millajoules equals to one jewel.

02:20 And so we're going to have jewel on top...