Science Questions

Factual Questions
1

I took a test today (ASTR) in which there were four questions out of 25 that I was not sure of, I could not find the answers in my textbook and I will not be able to fall asleep until I find the answer (on monday when class resumes). So maybe someone can help me rest my nerves…

Which of the following is not a basic force of nature?

A. strong nuclear
B. weak nuclear
C. Electromagnetism
D. gravity
E. gas pressure

I chose (A), strong nuclear. A decent guess since I had recently watch the history channel about the atomic bomb how scientists have to excite the atoms to cause such a rush of energy, so I figured strong nuclear forces do not happen naturally and not a basic force of nature. I could be wrong. The textbook did not address this issue.
One example of an emission line spectrum is that from

A. an ordinary (incandescent) light bulb
B. an electric stove burner
C. a human being
D. a neon advertising sign

The question was confusing to me, so I guessed (D)…the guess stemming from the fact that the topics at hand dealt with gas and light. Again I’m probably wrong.
Two rapidly moving atoms collide, exciting an electron in one atom to a higher enery level. Later this electron returns to its original ebergy level. What kind of spectrum does this process produce?

A. emission
B. absorption
C. continuous
D. none of the above

I chose © out of a pure 25% chance. I’m most likely wrong.
This next question is just stupid in my opinion.

A simple convex lens forms the image of a distant point source at a place called the

A. object point
B. focal length
C. objective
D. focal point

I chose (D) because the focal point was the only thing I remembered reading about in the text. I’m actually fairly confident in the answer.

2

E. The first four are all basic forces. Gas pressure, and other types of fource, arises from the others - electrical repulsion between the electrons in the gas molecules, f’rinstance.

D is correct. A “line spectrum” means the light source is emitting in a very narrow range of wavelengths. Light bulbs emit white light - many wavelengths. Burners and human beings emit as black bodies. They emit over a wide range of wavelengths. Burners glow red, and humans glow infrared, because of their temperatures. A neon sign, however, glows at a specific wavelength because of the energy levels of the neon electrons.

A is correct. When the electron returns to the lower energy state, it emits a photon.

D is correct.

3

The answer is E. Gas pressure is cause by electromagnetism. Specifically, the repulsion of like charges (electrons).

I’m going to have to go with D. Emission lines are observed by the excitation of elemental gasses and the like.

The answer is A. The atoms will me emitting photons, thus you observe an emission spectrum.

Definitely D.

4

Thanks a lot for the help. But I’m curious, does the “strong nuclear” forces have anything to do with the atomic bomb?

5

Sort of. The strong force is what keeps the nucleus together. Without it, the electromagnetic force would cause the protons to fly away from each other. The strong force is the strongest of all the fundamental forces, but it only works over very short distances, so it takes a lot of energy (read: particle accelerator or nuclear reaction) to get two like-charged subatomic particles close enough to “stick”.

6

So yes, in a way strong nuclear does have something to do with the atomic bomb, but I don’t think it’s in the way you were thinking, SoulSearching – the word “nuclear” in “strong nuclear force” refers to the fact that it is the force that keeps the nucleus of an atom together, rather than having anything to do with nuclear weapons specifically.

Hope my meaning is clear.

7

This is all true, but it’s phrased oddly. A light bulb filament is also emitting light as a black body- but as a black body with a temperature >3000 K, much hotter than the other two. This is a principal reason why they’re made of tungsten (which melts at ~3700K)- most other metals would melt or evaporate at that temperature.

8

Yes it has everything to do with a nuclear explosion. After absorbing a slow neutron the nucleus rearranges itself via the strong force so that its binding energy increases, and its potential energy decreases. The potential energy is then converted to kinetic energy and radiation.

9

The strong and weak nuclear forces aren’t terribly intuitive, because they only really matter on the atomic scale. Stephen Hawking’s A Brief History of Time is the standard introduction to this sort of thing.

10

This, it seems to me, is showing a very deep and fundamental misconception. There is no distinction between “man-made” and “natural”. At least, not in physics: There might be a distinction in ecology, say. You’re thinking of “nature” as “something that can happen without humans”. A better idea of “nature” would be “something that can happen”, period. All five of those things are things that can happen, so they’re all forces of nature. But gas pressure is an effect of electromagnetism, so it’s not fundamental (one could argue that all of the forces listed are just special cases of some Grand Unified force, but that goes above the level we’re at right now). As a rule of thumb, every force you ever actually encounter that isn’t obviously a gravitational force is electromagnetic in nature.

And since you said that you’re unfamiliar with the terminology in the lens question: The object point is just the location of the object (the thing you’re looking at), and the focal length is the distance from the lens or mirror to the focal point (I’m surprised this was also given as an answer choice: Too close to correct). The objective is the first lens or mirror that the light encounters, in a multi-element device like a telescope or microscope.