Week 2,3,4 Quantum World Achieve Question #5

[906168748]

The problem states, "How many photons with a. wavelength of 795 nm are needed to melt 409 g of ice? The enthalpy of fusion of water can be found in this table. So I started by finding the enthalpy of fusion in grams (333.6 J/g) and I multiplied the by the mass of ice (409g). I got 136442.4. Then, I converted 795 nanometers in to meters. I used the E= hc/lamba formula to find the energy of one photon. Once I found this number I divided 136442.4 by the energy of one photon to get the number of photons. I got 5.46 x 10^41. But it keeps saying that it is wrong. Where did I go wrong?

[Joyce Meng 2J]

Hello! Your steps look right, so it might have been a calculator error. Just to confirm, E = 2.5004 * 10^-19 J/photon after using the E=hc/lambda equation. Then, to find the number of photons, you do 136442.4/2.5004 * 10^-19 = 5.46 * 10^23. It looks like you just have a power error, so maybe check your h value (should be 10^-34) and c value (10^8).

[Aditya_Patil_3A]

The two main numbers to find are the energy of a single photon and the energy required to melt the entire block of ice. To find the energy to melt the entire block of ice, you multiply the enthalpy of fusion of water (333.6 J/g) by the mass of ice (407 g). Next, to find the energy of a single photon, you use the formula E = hv. However, since v is unknown, you can rearrange another equation to get that v is equal to the speed of light divided by the wavelength. Once you find the energy of a photon, you divide the energy required to melt the ice cube by the energy of a single photon to get the number of photons that have enough energy to melt the ice cube. You should get the correct answer if you use this method.

[906168748]

Thanks so much! That worked perfectly!