PV Gap

Melissa Said:

wind/solar power in Boston?

We Answered:

solar and wind generators for boats
http://www.made-in-china.com/showroom/hi…

Tara Said:

Is a resistor needed and if so, what size?

We Answered:

I'll answer question 2 first.
Resistors consume power, so if you want to maximize the number LED's you can connect then I would avoid using any resistors.
As for the first question. Anytime you draw current from a solar panel, the voltage will appear to drop. This is why it's reading 2.7 volts instead of 5 volts. If you measure the open circuit voltage of the solar panel with sufficient light it will read close to 5 volts.
It's hard to know how many LED's exactly you can put in series unless you know the exact voltage drop of each one. 5volts - 2.7volts = 2.3 volts which is approx .2 volt drop for each one. So theoretically you could put 24 or 25 in series. But it may be possible that you don't have to stop there. You may be able to connect another 24 in parallel with the first 24.
Try connecting 24 in series (or as many as you possibly can), then measure the current flow. If the current flow is less than the 30mA you originally measured, then I would predict you can put another row of LED's in parallel with the first. Then if that works then measure your current again and keep adding rows of LED's until the current approaches 50mA.

Good luck!

Bobby Said:

How do we know that our perception of the flow of time is the correct one?

We Answered:

It's a matter of proportion in these instances, remember if you will, the speed of light is 670 million miles an hour.

SIX HUNDRED AND SEVENTY MILLION MILES AN HOUR.
For relativity to do it's funky dance, we need to have a decent chunk of that as our own velocity. Now, the earth orbits the Sun at 67 thousand miles an hour. 67,000 into 670,000,000 gives 0.0001 - or 0.01%. That means time IS dilated, but by 0.01% (btw figures are all rounded a little)

The top estimate of the velocity of the Milky Way is about 1.3 million miles an hour. Fast, but again not overly significant.

So "our" time, vs. intergalactic time is off a little, but you aren't going to notice it without (sensitive) instruments.

Is this important? Yeah, kinda. Measuring the size and velocity of distant objects will need to be corrected to account for our motion.

From a philosophical standpoint, remember our time is correct, as all time is relative to the observer. It is relativity remember. ;)

Christy Said:

solar system questions?

We Answered:

Not that you'll actually learn anything, but:

7. b
8. f
9. a
10. h and i if you have been studying kepler, h is the better answer
11. a
12. a
13. can't see the picture, i don't know
14. i can't see the table, but c still looks way better than all the rest
15. G and H
16. i
17. b
18. trick question. if it slowed down, it would get closer to the sun, but getting closer to the sun would speed it up which would kick it back outward
19. out of the given options, d
20. i think i need an picture for this one
21. didn't i already ansewr this?
22. a is the least worst answer
23. g
24. c
25. g

Evelyn Said:

Is this uncalled for?

We Answered:

Yes. Just Ignore him.

Terry Said:

Are these answers in physical science correct? If not why?

We Answered:

1, 2, 3 are correct.
4 - d. 4 (Al is one atom and 3 atoms of chlorine make it 4)
5. Heat reqd. = ms(t2 - t1) = (12.5)*(0.125)*(100-20) = 125 cals.
6. correct
7. The specific heat of ethanol is 2.46 J/goC.
=> 890 = 16.6 * 2.46 * (t - 21.5) => t = 43.3 => a. 41 degree is correct.
8. correct.
9, 10 correct.
11. don't know.
12. double of your answer. You did not consider return path for echo to travel.