How Does Wireless Charging Work—And Is It Safe?

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by James Hunt

In 1899, the inventor Nikola Tesla began performing the first successful experiments on wireless power transfer. His initial success led him to believe that one day power would be transmitted around the planet without the need for cables. It took over 100 years, but his dream of wire-free power transmission was eventually realized—though perhaps not by the methods he envisioned.

When creating phones and tablets, manufacturers are faced with the challenge of giving the device a long battery life, keeping it lightweight, and making charging as painless as possible. Wireless power, which makes recharging your phone as easy as putting it down, could be the solution to that last part. But how does it actually work? And, perhaps more importantly, how safe is it?

Modern wireless power draws on the same principle that Tesla investigated over a century ago: induction. Electromagnetic induction—using an electromagnetic field to transfer power between two objects—forms the basis of all modern wireless charging, as well as things like contactless payment, cooktops, and wireless speakers.

In a practical sense, the way induction works is simple: First, you feed power to a base unit or charging station that contains a “transmitter” coil. An electromagnetic field forms around the transmitter and when a second “receiver” coil comes near enough, the receiver coil interacts with the magnetic field to create an electric current. By putting the second coil inside another device, you can wirelessly transfer power from the base to the device.

Most induction chargers only operate over a short distance, however, and while physical contact between a device and its base unit isn't necessary for induction to work, the fields generated lose so much power as the devices get farther away that it's usually the only way to get the two coils close enough.

As for safety, there's really nothing to worry about. The average induction charger creates a field no more dangerous than radio waves, and it isn't strong enough to have any effect on the human body. If anything, plugging in and unplugging a cable is more dangerous because there's a minute chance it could fray and shock you. By contrast, induction hardware can be safely encased in thick plastic and still work. This is why electric toothbrushes have long used induction to charge: The units can remain sealed and waterproof.

Sounds great, right? So why don't we use wireless charging all the time? For starters, it’s slow going. While wireless charging has improved dramatically over the past few years, wired charging is still generally faster. Also, the process creates a lot of waste heat, so much so that some Samsung charging pads have fans to keep everything cool.

The big issue is practicality, though. You can easily use your phone while it's plugged into a charger, but it's tricky to hold your phone up to your ear while it's resting on a wireless base station.

But things are changing.

Returning to Tesla's original experiments, an effect called Resonant Inductive Coupling allowed the inventor to safely transmit power over several meters. Perhaps the most popular wireless charging standard, Qi, has recently been updated to allow a version of this to be implemented in compatible devices. The result is that the charging range has increased to four centimeters.

It might not sound like much, but it's a start. In the future, wall-sized charge stations might be able to transmit power to multiple devices in multiple rooms as you move about your house. It may have taken over a century to get to this point, but we're closer than ever to wireless power transfer becoming commonplace. It's what Tesla would've wanted.

12 Creative Ways to Spend Your FSA Money Before the Deadline

stockfour/iStock via Getty Images
stockfour/iStock via Getty Images

If you have a Flexible Spending Account (FSA), chances are, time is running out for you to use that cash. Depending on your employer’s rules, if you don’t spend your FSA money by the end of the grace period, you potentially lose some of it. Lost cash is never a good thing.

For those unfamiliar, an FSA is an employer-sponsored spending account. You deposit pre-tax dollars into the account, and you can spend that money on a number of health care expenses. It’s kind of like a Health Savings Account (HSA), but with a few big differences—namely, your HSA funds roll over from year to year, so there’s no deadline to spend it all. With an FSA, though, most of your funds expire at the end of the year. Bummer.

The good news is: The law allows employers to roll $500 over into the new year and also offer a grace period of up to two and a half months to use that cash (March 15). Depending on your employer, you might not even have that long, though. The deadline is fast approaching for many account holders, so if you have to use your FSA money soon, here are a handful of creative ways to spend it.

1. Buy some new shades.

Head to the optometrist, get an eye prescription, then use your FSA funds to buy some new specs or shades. Contact lenses and solution are also covered.

You can also buy reading glasses with your FSA money, and you don’t even need a prescription.

2. Try acupuncture.

Scientists are divided on the efficacy of acupuncture, but some studies show it’s useful for treating chronic pain, arthritis, and even depression. If you’ve been curious about the treatment, now's a good time to try it: Your FSA money will cover acupuncture sessions in some cases. You can even buy an acupressure mat without a prescription.

If you’d rather go to a chiropractor, your FSA funds cover those visits, too.

3. Stock up on staples.

If you’re running low on standard over-the-counter meds, good news: Most of them are FSA-eligible. This includes headache medicine, pain relievers, antacids, heartburn meds, and anything else your heart (or other parts of your body) desires.

There’s one big caveat, though: Most of these require a prescription in order to be eligible, so you may have to make an appointment with your doctor first. The FSA store tells you which over-the-counter items require a prescription.

4. Treat your feet.

Give your feet a break with a pair of massaging gel shoe inserts. They’re FSA-eligible, along with a few other foot care products, including arch braces, toe cushions, and callus trimmers.

In some cases, foot massagers or circulators may be covered, too. For example, here’s one that’s available via the FSA store, no prescription necessary.

5. Get clear skin.

Yep—acne treatments, toner, and other skin care products are all eligible for FSA spending. Again, most of these require a prescription for reimbursement, but don’t let that deter you. Your doctor is familiar with the rules and you shouldn’t have trouble getting a prescription. And, as WageWorks points out, your prescription also lasts for a year. Check the rules of your FSA plan to see if you need a separate prescription for each item, or if you can include multiple products or drug categories on a single prescription.

While we’re on the topic of faces, lip balm is another great way to spend your FSA funds—and you don’t need a prescription for that. There’s also no prescription necessary for this vibrating face massager.

6. Fill your medicine cabinet.

If your medicine cabinet is getting bare, or you don’t have one to begin with, stock it with a handful of FSA-eligible items. Here are some items that don’t require a prescription:

You can also stock up on first aid kits. You don’t need a prescription to buy those, and many of them come with pain relievers and other medicine.

7. Make sure you’re covered in the bedroom.

Condoms are FSA-eligible, and so are pregnancy tests, monitors, and fertility kits. Female contraceptives are also covered when you have a prescription.

8. Prepare for your upcoming vacation.

If you have a vacation planned this year, use your FSA money to stock up on trip essentials. For example:

9. Get a better night’s sleep.

If you have trouble sleeping, sleep aids are eligible, though you’ll need a prescription. If you want to try a sleep mask, many of them are eligible without a prescription. For example, there’s this relaxing sleep mask and this thermal eye mask.

For those nights you’re sleeping off a cold or flu, a vaporizer can make a big difference, and those are eligible, too (no prescription required). Bed warmers like this one are often covered, too.

Your FSA funds likely cover more than you realize, so if you have to use them up by the deadline, get creative. This list should help you get started, and many drugstores will tell you which items are FSA-eligible when you shop online.

10. Go to the dentist.

While basics like toothpaste and cosmetic procedures like whitening treatments aren’t FSA eligible, most of the expenses you incur at your dentist’s office are. That includes co-pays and deductibles as well as fees for cleanings, x-rays, fillings, and even the cost of braces. There are also some products you can buy over-the-counter without ever visiting the dentist. Some mouthguards that prevent you from grinding your teeth at night are eligible, as are cleaning solutions for retainers and dentures.

11. Try some new gadgets.

If you still have some extra cash to burn, it’s a great time to try some expensive high-tech devices that you’ve been curious about but might not otherwise want to splurge on. The list includes light therapy treatments for acne, vibrating nausea relief bands, electrical stimulation devices for chronic pain, cloud-connected stethoscopes, and smart thermometers.

12. Head to Amazon.

There are plenty of FSA-eligible items available on Amazon, including items for foot health, cold and allergy medication, eye care, and first-aid kits. Find out more details on how to spend your FSA money on Amazon here.

Mental Floss has affiliate relationships with certain retailers and may receive a small percentage of any sale. But we choose all products independently and only get commission on items you buy and don't return, so we're only happy if you're happy. Thanks for helping us pay the bills!

5 Easier Ways to Water Your Christmas Tree

Artfoliophoto/iStock via Getty Images
Artfoliophoto/iStock via Getty Images

A decorated Christmas tree adds instant holiday cheer to any room—for a few days, at least. If you neglect to care for it, however, it doesn't take long for that tree to start dropping needles and dry up into a brittle, brown fire hazard. The key to keeping your tree looking healthy until the New Year is to water it every day. Of course, that comes with its own problems, like sap-covered clothing and sore knees. Here are some alternative methods for watering your Christmas tree that won't have you wishing for the end of the holiday season.

1. Rig a funnel and PVC pipe.

The worst part of watering a Christmas tree is crawling around on your hands and knees, but once you've set up this funnel rig, you can water it while standing up. As Eric Palonen demonstrates in the video above, all you need to do is stick a PVC pipe into the tree stand, attach a funnel to the other end with an elbow connector, and pour in the water.

2. Dig out a pool noodle.

Don't have a spare PVC pipe at home? A foam pool noodle works just as well as the receptacle for your funnel.

3. Disguise a DIY water dispenser as a present.

On Instructables, Rickyspears shares his step-by-step process for building a Christmas tree-watering rig. Using a bucket and plastic tube with brass fittings, you can create a water-siphoning system that automatically keeps your tree hydrated. And because a big bucket of water beneath the tree isn't the most festive sight, Rickyspears also tells you how to disguise it by hiding it in a box decorated with wrapping paper.

4. Use a wine bottle.

Still have some leftover wine bottles from Thanksgiving (or the weekend) lying around the house? Use one of them to water the base of your tree while keeping a safe distance between you and the sticky branches. (Though if you do get some sap on your hands, there are a few easy ways to get rid of it.)

5. Invest in an automated watering system.

DIY watering rigs are inexpensive, but if convenience is your main concern, it's hard to beat a product that was designed just for this purpose. The Christmas tree watering bag from Elf Logic senses when your tree needs water and replenishes it automatically. Plus, it hangs on a branch like an ornament, making it easy to tuck away.

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