Recent content by JFS321

Dave, thanks. I do think both websites, although they are saying the same thing, are incorrect. I am good with total power. The magnification formula I give would only be used (I'm assuming) when you need to determine magnification of a printed image with a scale bar, and the total power...

Perhaps this should be in the Biology forum, but I'm thinking that you physicists can give a more reliable answer here. The magnification equation for microscopes is: M = I/A (image size divided by actual size). This seems very easy and intuitive. By this equation, if the image size was...

Thanks for all of the help!

Thanks. All of this makes good sense. When you said "for all we know we picked only as many different marbles as the number of different colors..." ... Do you mean if we had 100 red, 50 blue, and 10 green, we may have picked the same 3 red, blue, and green marble each sampling event?

Also, let me be sure I am clear on this. There are only about 25 marbles in the bag -- by having them draw/replace 50x, am I increasing my statistical power because we are much more likely to get a ratio that is closest to the actual ratio in the bag? I think it's the "pretending" part that is...

Ok, thanks a lot. I think I can make sense of that -- basically, if we did dump out all the marbles (I'm not going to do it that way, but...), those marbles would theoretically represent a random sample from the larger population. Then the Chi sq can tell us the probability getting those...

Hi all, I'm a high school physics / AP biology teacher looking to expand my understanding of the Chi-square test some. I planned an activity in which students are randomly drawing colored marbles out of a bag in order to see if they match predicted ratios (2:1, 1:1, others). I'm having them...

0 and 1 represents the means AND the standard deviations, or just the standard deviations?

All, https://jimgrange.wordpress.com/2015/12/05/statistics-tables-where-do-the-numbers-come-from/ This is a great post -- but I'm a little foggy on the sentence that says "...mean and standard deviation for each condition is fixed at 0 and 1." Can someone explain this in a slightly different...

Amazing technology. Thanks!

Sorry for not originally being more clear. Tom, that does help and got me Googling pixels. I didn't know that pixels use phosphors to produce the red, green, and blue wavelengths. That makes sense now. I didn't understand how the computer was controlling the wavelengths themselves (because...

I have both my iPhone and desktop computer set to a "night light" mode, and obviously my eyes appreciate the warmer colors at night. But what I'm wondering is this: Do they actually work? Here's what got me thinking: I have a pair of Elvex glasses rated to block all blue wavelengths, and I...

Thanks to all. I think my original mistake was idealizing the problem -- i.e., the superhero and train magically stop instantaneously. It's more intuitive now to think of the real-world effects of deformation, etc. and how those clearly relate to work and energy.

All, I started this strange little thought experiment this morning, but I'm not quite sure what I'm missing. Here's the problem I solved (this is not homework, BTW): Find the speed at which a super hero (mass=76.0 kg) must fly into a train (mass = 19,537 kg) traveling at 35 m/s to stop it ...

I did find these on Amazon, and I could power them with 4 AA batteries in series (another good lesson for students to figure out). https://www.amazon.com/dp/B009AQLDSS/?tag=pfamazon01-20 To make things easier, I do have 9 V battery connectors. Other than increasing RPM, would there be any...