Score
Title
435
AskScience Panel of Scientists XVII
3110
Is there a limit on how long a power cord can be?
1398
I know it takes two weeks for the flu vaccine to be fully effective. I assume effectiveness is zero right before the vaccine is administered, and maximum after two weeks. But is there a graph that shows how effectiveness changes in time?
8651
Why is the Congo River so deep?
17
Why the Antarctic ice cap stays in one place and does not drift freely like an iceberg?
42
Why is the separation constant for the radial equation of the Hydrogen atom in the form of L(L+1)?
11
Why can some viruses (smallpox, polio) be virtually eradicated while others cannot (HIV, influenza)?
3
How does a coax splitter work?
20
If the capacity of a battery charging another battery drops below that of the receiving battery, will it stop transferring electricity since the electrons will no longer prefer to leave the lower energy "state" of the drained battery?
3
Is there a link between a metal being conductive from an electric standpoint and it being magnetic? If so, what is the cause?
13
If our bodies are conductive, can holding a battery between two fingers deplete it completely?
2
What can stop and/or destroy a black hole?
40
How/why are so many mathematical proofs and theorems contingent on the Riemann hypothesis being true?
7438
Are there any predators that hunt for sport rather than for food?
6
Are there any ant species that don’t live in colonies?
24
Do they update the voyager software?
2
How did the Russian Woodpecker receiver work?
2
What is meant by the heat death of the universe?
19
Does language affect learning and studying?
2
If the strength of an acid is based on concentration, why are acids like Sulfuric Acid always considered so dangerous compared to others?
23
When water does down the drain, why does it always go down the drain in a form of whirlpool.?
12
From what I have learnt so far, refrigerators use chlorofluorocarbons for cooling. Do these chlorofluorocarbons run out after some time? If yes how are they replenished?
0
Microwave Ovens and Wi-Fi Signals Operate at The Same Frequency (2.4GHz). What Makes Microwave Ovens More Dangerous?
20
What makes things transparent?
16
What allows certain cars and airplanes to have their own Wifi?
31
What causes the thick mist/fog that I frequently see coming off of mountains in my area?
9
What exactly happens to a person's behavior after a lobotomy?
8
How Bayes rule was used to help with aiming cannons?
6
Is there a limit to the energy density of batteries?
3
Is a Colliod a state of matter?
0
What kind of waves on the Electromagnetic Spectrum do metal detectors use to isolate only metal and no other materials?
21
Many poisonous and venomous vertebrates get their toxins from toxic arthropods that form part of their diets. Why can't they just form the toxins themselves the same ways their prey do?
192
Why are hail storms so short?
6
How do particle accelerators such as the LHC detect particle collision products?
5
How do marine mammals keep their testes cool?
68
If aliens were to look at earth through a telescope from 65 million lightyears away, would they see dinosaurs?
13
Why does fire flicker?
27
What exactly is string theory and how does it work?
10732
What exactly does the cold virus do to me to make me so weak?
8
I understand conduction and radiation as modes of heat transfer, but convection confuses me. Why does fluid moving over an object remove heat from it as opposed to adding heat due to friction?
17
What happens to the brain as you fall asleep? Are certain proteins released to induce sleep? Is it seen as a voluntary or involuntary action?
8 whitcwa Most lasers are a narrow beam, but all have some divergence. The only rays which are emitted are ones which are travelling nearly parallel to the cavity. Laser diodes have short cavities and have up to 30 degrees divergence. They must be collimated with a lens.
5 Marlsfarp Well first if all, it isn't just a straight line. Light is a wave and all waves diffract, so it does spread out. There is a theoretical limit to how *little* a wave can spread out, and that is called a "Gaussian beam". In an ideal beam (which a good quality laser will get very close to), the angle it spreads out is given by (wavelength)/(pi * aperture size). This is the size of the "spot," but there are small amounts the radiate in every direction, as well. Notice that as the aperture size decreases, the angle increases. So as a point source, it really would spread in all directions equally. But it isn't a point source, it's an aperture of finite size, and the "front of point sources" (per Huygens) interfere constructively and destructively.
9 0 whitcwa Most lasers are a narrow beam, but all have some divergence. The only rays which are emitted are ones which are travelling nearly parallel to the cavity. Laser diodes have short cavities and have up to 30 degrees divergence. They must be collimated with a lens.
5 0 Marlsfarp Well first if all, it isn't just a straight line. Light is a wave and all waves diffract, so it does spread out. There is a theoretical limit to how *little* a wave can spread out, and that is called a "Gaussian beam". In an ideal beam (which a good quality laser will get very close to), the angle it spreads out is given by (wavelength)/(pi * aperture size). This is the size of the "spot," but there are small amounts the radiate in every direction, as well. Notice that as the aperture size decreases, the angle increases. So as a point source, it really would spread in all directions equally. But it isn't a point source, it's an aperture of finite size, and the "front of point sources" (per Huygens) interfere constructively and destructively.