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Q & A: battery-powered lights

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Most recent answer: 09/23/2014
Q:
I am thinking of powering two 25 watt halogen bulbs using a lawn mower battery or possibly a motorcycle battery. I need it to remain as light as possible to keep it easily mobile. How long would one of the batteries give me light?
- Brandon (age 29)
Verona Ky
A:
It looks like typical largish motorcycle batteries store about 12 A-hr of charge, giving about 150 W-hr of energy. With two 25 W bulbs, you'll maybe get 3 hours of power, tops.

If instead you invest in 12V LED lights with the same light output as those halogen bulbs, you'll use less than 1/4 of the power, and can run at least 4 times longer with the same battery, or switch to a smaller and lighter battery. The disadvantage is the higher initial price, so it might not be worth it unless you intend to use the system a lot.

Mike W.

(published on 06/03/2012)

Follow-Up #1: Several questions about nuclear physics

Q:
This is the first in a series of questions I have developed from material I've read. I read that protons and neutrons are stable when in atoms and do not decay as when they are free. I read that their constituent quarks are also stable when inside of an atom and do not decay. My question is on the gluons, which exchange the color force for the quarks. Do gluons decay in an atom or are gluons stable in an atom because the quarks, neutrons, and protons are stable? Does this mean if I walk across a room I will have the same gluons in me/my atoms like my neutrons, protons, and quark in my atoms will be the same ones when change location? Thanks!
- Travis Stanislaus (age 26)
Richland, WA
A:

Hello Travis,

As for your first question, it's a matter of conservation of energy and other quantum conservation laws. As an example a free proton could in principle decay into a positron and a gamma ray.  But it doesn't because of the  conservation of lepton number: the proton and photon both have zero lepton number whereas the electron has value of one.  On the other hand a neutron can cheerfully decay into a proton, plus an electron and an anti-neutrino.   Energy is conserved as well as lepton conservation: the electron has plus one and the anti-neutrino has minus one.   The same for quarks.  A quark inside a nucleus doesn't have anything to decay into energetically.  A top quark quark, on the other hand, produced by a high energy collision at Fermilab or the CERN collider can decay into all sorts of secondary particles.

Gluons, like photons, are the carriers of the strong and electromagnetic forces.   A "virtual" photon can decay into electron-positron pairs, whereas a "real" photon like one coming from a laser would have to interact with some other charged body in order to produce electron-positron pairs.  In nuclear particles there's a spread of possible values that could result from a "measurement" of the numbers of gluons and internal photons, just like for many quantum variables.

 

LeeH


(published on 09/19/2014)

Follow-Up #2: cave lights

Q:
Years ago I used a very powerful cave diving light. It was made of a 12 volt motorcycle battery and a 250 watt aircraft landing bulb. I want to make another powerful light like the old one. Here is my question: I can find 250 watt aircraft landing bulbs, however they are all 13 volts. Will a 12 volt motorcycle battery power it up? I know the burn time will be just over 1 hour, but that is fine for illuminating large underwater cavern rooms. Thanks in advance for your answer.
- Bill Anderson (age 65)
Ocklawaha, Fl USA
A:

The actual voltage on your motorcycle battery will be a little over 12V, when fully charged. So it should work ok with  that bulb. For this purpose I'd very strongly recommend, however, scrapping the bulb and replacing it with some LED lights. For a given battery charge and light output, they will last about 4 times longer. After just hearing many near-death tales from a spelunking friend, I'd say you want all the extra time possible for unforeseen events.

Mike W.


(published on 09/23/2014)

Follow-up on this answer.