Recent content by kuruman

Choice (B) is a bit ambiguous. To go to extremes, Tellurium-128 has a half-life of ##7.7\times 10^{24}## years via double beta decay. If I am given a sample, I "know" theoretically that it has started to decay but, arguably, the sample "has started to decay" as soon as I observe the first decay...

A figure sure helps.

OK, let's backtrack and write some equations. For part (a) you can write $$\mathbf E=\left[\sin\left(t+\frac{\pi}{4}\right),\sin(t)\right].$$ A parametric plot gives the figure on the right which is what you have shown in post #3. What equations will you get if you line up: 1. The quarter-wave...

Where did you get this stuff? What does it mean in relation to your question? What red dots?

You know that the phase difference between the two components is ##\frac{\pi}{4}.## What phase difference do you need in order to get linear polarization? What does a half-wave plate do to the phase difference? How would it change the trajectory? What does a quarter-wave plate do to the phase...

Can you plot the trajectory of point (Ex,Ey) as suggested in part (a)? What shape do you get? If so, can you do the same for for part (b)? What shape do you get in this case? Also, please provide the statement of the problem as was given to you. What comes before parts (a) and (b)?

You might also consider cleaning the conducting disk or ball on top of the electroscope with acetone to remove any gunk that might have collected there.

I think that the drawing would be more accurately drawn if the lightning hit the tree instead of the ground on its left. As negative charges build up at the base of storm clouds, they induce a swell of positive charges, or "streamers," to rise from the ground. Taller, more conductive objects...

Yes, of course. I was thinking of something else. It's late where I am. Good night.

Shown on the right is an excerpt from a January 13, 1920 New York Times editorial lambasting Robert Goddard's for his suggestion about firing rockets in space. The author of this unsigned editorial seems to think that Goddard's scheme will not work because in vacuum there is nothing to push...

Yes. In the inertial frame where the rocket is initially at rest and no fuel has been spent, the total momentum is zero and must remain zero at all subsequent times. In that frame, the very first ##dm## of spent fuel has speed ##u_0## and the accelerating rocket cannot move faster than that in...

The rocket equation in the absence of external forces is $$m\frac{dv}{dt}=(u-v)\frac{dm}{dt}$$where ##m=~## instantaneous mass of the rocket + unspent fuel ##v=~## instantaneous velocity of the rocket relative to an inertial frame ##u=~## instantaneous velocity of the exhaust gas relative to the...

Here is an easy to understand example. There are 20 boxes of books, each of mass 20 kg, that need to be moved to an apartment 10 meters above ground. There is no elevator. A powerful weightlifter might stack 5 boxes on top of each other and finish the job in 4 trips and 20 minutes total. An...

The second expression is the leading term of a series expansion of the first term. If you use the first term, you can't go wrong because it is exact. The second term gives an estimate for ##Q## which becomes rougher as the ratio ##~\beta/\omega~## gets closer to ##1##. Is that what you wanted...

To determine the direction of the gravitational field, also known as "down", you suspend a mass from a string and you deduce that "down" is the direction from the point of support to the attached mass at equilibrium. This device is also known as a plumb-bob. The picture below is modified from...