Quantum Tunnel Answers: Fresnel Lens

Hello everyone,

once again we have a question coming to the inbox of the Quantum Tunnel blog. If you are interested in asking a question, please feel free to get in touch using this page. We have once again a question by a very avid reader, let’s take a look:

Dear Quantum Tunnel,

Could you please explain how Fresnel lenses work? I am asking after listening to Dr Carlos Macías-Romero talking in one of the Quantum Tunnel podcasts. Thanks a lot.


Hello yet again Pablo, thanks a lot for your question. Well, I assume that you are familiar with the idea of a lens and that you may even wear a pair of spectacles or know someone who does and so you know that you can correct, among other things, the focal point and thus read your favourite blog (the Quantum Tunnel site of course!) with trouble.

Well, have you ever had a chance to go and see a lighthouse close enough? But not just the building, the actual place where the light is beamed out to see? If so you may have seen the lenses they use. If not, take a look the image here:

Lighthouse Lens
Lighthouse Lens (Photo credit: Wikipedia)

You can see how the lens is made out of various concentric layers of material and the design allows us to construct lenses that otherwise would be way to thick and therefore heavier. A lighthouse requires a light beam that uses a large aperture but a short focal length and a Fresnel lens offers exactly that without the need of a really thick lens. Fresnel lenses are named after the French physicist Augustin-Jean Fresnel.

Another example of Fresnel lenses are flat magnifying glasses such as the one shown below, you can see that they are effectively flat and no need to use one such as those used by Sherlock Holmes…

English: Creditcard-size Fresnel magnifier Ned...
English: Creditcard-size Fresnel magnifier Nederlands: Fresnelloep in creditcardformaat (Photo credit: Wikipedia)

The design of a Fresnel lens allows it to capture more oblique light from a light source. Remember that a lens works by refracting (bending) the light and the way in which the “layering” in the Fresnel lens helps with the refraction needed. See the diagram below:

Fresnel lens

A couple of other uses for these lenses are in overhead projectors and the headlights of cars. So next time you attend or give a lecture or drive at night, think of Monsieur Fresnel.

Quantum Tunnel Answers – Interest in Quantum Physics

This time is not really a question that has arrived to the Quantum Tunnel mailbox, it is rather an observation and some cheers. Let’s take a look:

Dear Quantum Tunnel,

I have listened to all the available Quantum Tunnel podcasts in Spanish, the content is great and the news are cool. I am interested in understanding more about quantum theory and in my experience there is no a lot of information at my level that does not make it all sounds like philosophy or even a bad example. In most cases the explanations start up assuming that one does understand the “quantum concepts”. With those limitations, I am afraid to admit that I actually fail to see the genius of Einstein. Having said that I refuse to think that after I am unable to understand ideas that are thought in universities. Surely some explanations do not start with “time is relative”. If thousands can understand it, so can I.

Pablo Mitlanian

Hello again Pablo, I agree with you that there is a lot of information out there that either assumes too much, or simply exploits the concepts for non-scientific purposes. You are right, I am sure you can understand the intricacies of quantum-mechanical phenomena, but bear in mind the words of Richard Feynman “I think I can safely say that nobody understands quantum mechanics”.  I would not expect someone to become a quantum physicist without the appropriate training, in the same way we cannot all perform a heart transplant without studying medicine and practicing. That doesn’t mean we can’t change careers though!

If you want to learn quantum theory in ten minutes, take a look at the blog post that the Quantum Pontiff blog posted a few years back. Yes, there are ducks and turkeys, but then again they promised to explain in 10 minutes. There are nonetheless a few things that can serve as building blocks to achieve your goal:

  1. Learn about classical physics (yes, the courses on mechanics that you probably took in high school, exactly those). A good understanding of this will highlight those non-intuitive results from the quantum world.
  2. Understand how to describe the behaviour of particles and of waves (I guess this is part of number 1 above, so just stressing the point!)
  3. Make sure you are well versed in the use of probability (yes, I am saying that you need to revise some mathematics!)
  4. Be patient!

It all that works, perhaps consider enrolling at your local University to read physics, you never know you make the next discovery in physics. Incidentally, within your revision make sure you understand that relativity theory (general or special) is completely decoupled from quantum theory. As a matter of fact, joining the two is one of the biggest challenges in physics today.

If you want to ask a question to Quantum Tunnel use the form here.

Quantum Tunnel answers: Solar flares

I am very pleased that the first (of many I hope) questions has arrived to the mailbox of the Quantum Tunnel blog. So here we go:

Dear Quantum Tunnel:

Is it true that there will be a solar storm in December (2014) and there will be three days of darkness? If so, why is this happening?

Yours sincerely,

Pablo Mitlanian

Well, thanks a lot for your question Pablo. Let me first start by clearing the air and respond directly to the question: No, it is not true that there will be a solar storm that will cause three days of darkness. So there you go! I think this is a rumor that has been going around the interwebs for quite some time. Neither NASA nor any other respected scientific institution has made such a claim.

Now, let us address the actual facts related to the question: solar storms do indeed exist and they usually refer to sudden release of energy from the surface of the Sun, we are talking about 6times 10^{25} Joules. To put this in perspective, the impact in Chicxulub (Mexico) that caused the mass extinction of the dinosaurs is around 1times 10^8 Joules. Solar flares are sometimes followed by the ejection of plasma from the upper atmosphere of the Sun (called solar wind) and accompanying magnetic fields. The particles that make up the solar wind (electrons, ions and atoms) reach the Earth one or two days after the event. Incidentally, the charged particles hitting the magnetosphere are the reason for beautiful auroras!

Magnificent CME Erupts on the Sun - August 31


As you can imagine, solar flares have a definite impact on space weather locally, and thus on the Earth too. The particles from the solar wind can impact with the Earths magnetosphere and present some hazard to spacecraft and satellites and in some cases affect the terrestrial electric power grids. One of the most powerful solar flares observed was recorded in 1859 by Richard Carrington and, independently, Richard Hodgson and the auroras could be seen even in Cuba and Hawaii!

The Sun’s magnetic activity has been observed to follow a periodic cycle of about 11 years and on a maximum there are more solar flares. The last maximum was in 2000 and we were thus expecting a maximum around 2011, but as with other weather (terrestrial or not) predictions, there is a margin of error. So, I am sure you can go around doing your end of year celebrations without worrying about solar flares and who knows you may even have a chance to see a charming aurora!



If you want to ask a question to Quantum Tunnel use the form here.

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