If you connect a headphone to your phone, does it drain the battery? How does a headphone work?
A pair of headphones is basically a set of small speakers held onto your head with a headband. Now, the battery drainage depends on the headphones you get. A generic, cheap pair of headphones will usually have a low impedance (<20 ohms). This means that they can be driven very easily by mobile devices and can get loud without draining battery. These are more available in the average consumer market because they are cheap to manufacture and people won’t complain about them being too quiet. Headphones at this tier are basically earbuds that go over your head, and will not drain your battery any faster than a pair of earbuds would.A higher quality “studio” or “audiophile” set will usually have a larger impedance (>36 ohms). These headphones require more power to drive, but will give a clearer sound and less distortion. Since it requires more power to drive, it will be pretty quiet unless you turn up the volume, and this is what drains the battery. If the impedance goes over 60 ohms, you will need to use a headphone amplifier to be able to listen to anything at a reasonable volume. An extreme example would be a PA system. You wouldn’t be powering these with your phone; they have to be connected to an external power source.The battery drainage all depends on the headphones you have. My pair of AKG 553 have an impedance of 36 ohms, and they drain my battery at a moderate level, meaning I will be from a full charge to around 40% in 5 hours. My earbuds, which have around 16 ohms impedance, can pump sound pretty loudly for a whole day and only drain my phone to around 60%. Now, if I were you, I would be more concerned about the app that you are using to listen to music or do whatever else you do with headphones. Youtube is incredibly battery-hungry. A couple videos in half an hour and I’m already at 80%. If I’m just listening to music from Spotify, I would only drop 5% in that time. Hope this helps.
Are wireless signals (e.g. Bluetooth and Wi-Fi) harmful to the human body?
Let's look at this top down:There about 4.3 Billion mobile/cellular phones in use world wide, and there have been over a Billion phones in use since about 2001. Their frequencies are range from 400 MHz (0.4 GHz) to 1.9 GHz, roughly similar to your router.There are about 300 million laptops sold each year, with >90% having 2.4 GHz WiFi. There are roughly 1.2 Billion in regular use world wide, and there have been over 500 million using Wi-Fi the past 5 years.So far, we have not seen any mass epidemics, except for obesity, which is usually attributed to people spending too much time sitting and playing with computers.So the experiment Daniel Helman talks about has been running for some time, with large statistical power (now Billions!) and the results appear to be negative.Parts of the experiment have been running long enough (30 years) that we can put an upper bound on how bad the worse case to be. The worse possible case at this point (early 2012) would be some what bad for a small number of people, probably less that 500,000 out of the Billions.There is not a mega disaster waiting, or it would have already occurred.******In the real world, Microwaves (like 2.4 and 5 GHz) have been known to affect the eyes, being associated with cataracts. One reason you are not supposed to put your head next to a microwave oven and stare at the food.You are very close to the router for a long period of time.> I would suggest you consider moving the router to the other side of the room, or toward your feet, and away from delicate and important systems like eyeballs, brains, ears, etc.That's a low effort precaution.*****Since you live in Los Angeles, where the car is king, here's an idea that might have more "impact" on your personal safety: get a modern car.1959 Chevy vs. 2009 Chevy frontal offset crash...
Why would I buy a 1-amp USB charger instead of a 2.1-amp charger?
Your understanding is good. USB voltage is always 5V so only current (amps) matter while charging your USB device.In short, with more amps, the charge will be quicker.However, charging lithium batteries is not that simple. There’s a chip that control the charging process, or more exactly charging cycles : there are 3 phases for charging.Pre Charging - Fast charging - Charge terminationThis is only during the 2nd phase (fast charging) that the charge controller chip will allow the maximum current to flow. During pre charging and charge termination phases, the current will be reduced and using a 3 amps or 0.5 amps will not matter very much.Amps curve is the red one.That said, fast charge phase is the most important one (80 - 90% of the battery charging process). Also, this is the charge controller chip that will decide how much amp it will accept as a maximum (to prevent over heating etc.). If the chip inside your i-device is rated up to 1A, using a 2A USB charger will change nothing.The link you provide shows a 2 x 0.5 amp per USB port for the 1A charger. My guess is that the 2.1A version is 2 x 1.05A per USB port. With 1$ difference I would go with the 2.1A version.Personally I use a 2A USB charger for my smartphone and tablet.