Why do electrons (and other very small particles) sometimes behave as particles (i.e. when we are not looking at them) where as other times they behave as waves?

Suppose that an electron with spin up emits a photon in the field of an ion (bremsstrahlung). What is the spin of the emitted photon? Is it correct to say that the photon is circularly polarized if the spin of the electron flips down and linearly polarised if it remains up?

This questions started with a question I had about gravity. If two objects of different weights fall to the earth at the same rate of acceleration, then it seems to me that gravity is in some ways 'calculating' the weight of each item and applying the appropriate force to each item so as to have it fall at the same rate of acceleration. Is this true (or at least close to the truth)?

This got me think that perhaps this is what all of the mathematical equations of physics are really saying - namely that there are mathematical equations that are getting applied to the real world in one way or another.

Is this right? If not, why not?

A point charge of -4.00nC is at the origin, and a second point charge of 6.00nC is on the x axis at x = 0.830m . Find the magnitude and direction of the electric field at each of the following points on the x axis.

a. x= 16.0 cm

b. x = 1.20m

c. x = -22.0cm

find the electric field a distance r from a line of a positive charge of infinite length and constant charge per unit length lambda ?

From Michael on Skeptics Stackexchange:

How about a wire that's grounded? Safe to touch, right? WRONG.

________________ 30 amps -> ________________
| |
+ |
220V Load
- |
|______(YOU ARE HERE)______<- 30 amps________|
|
Ground

The wire you touched was not only at 0 volts, but also grounded, and yet, you are feeling pretty shitty in this diagram. You have ceased to be as a human, and you are now a part of a circuit, functioning as part of a return leg (pictured above) or as a "parallel path to ground" (not pictured above.)

I don't get how this can work. If the wire is at 0 volts and you are at 0 volts, then there is no potential difference and hence I'd expect no current. Is this physics correct?

My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people passing through a particular point per unit time. Voltage = the (change in) number of sandwiches per person. In a parallel circuit the number of people (current) is divided between the two paths, but the number of sandwiches per person (voltage) remains the same. In a series circuit the number of people passing through a particular point remain the same, but they drop off a certain percentage of their sandwiches at every resistor. Therefore, there is a voltage drop that occurs between the points before and after every resistor.

This analogy naturally leads to the question: how do the electrons "know" that they are going to have to share their voltage between two resistors before they reach the second one? (In other words, not drop off all their sandwiches at the first resistor they find)

For example it is stated that if supersymmetry breaking is soft then stability of gauge hierarchy can be still maintained.

Imagine, if you will, a string background with an extremely tiny value for the string coupling. The Planck scale is many orders of magnitude smaller in size than the string scale. Is the UV/IR mixing scale the Planck scale, or the string scale? What happens at intermediate scales?

Gravitons are string modes, and as such, their spatial extent is the string scale. They can never resolve anything smaller than that. On the other hand, D-branes are more sensitive

A 80 kg man weighs himself at the north pole and at the equator. Which scale reading is higher? (The radius of the earth at the equator is 6.37 x 10⁶m). By how much? ____N

Find the electric field (magnitude and direction) for the following situations:

A) At a point 1.0x10-3 m away from a 5.00 pC charge. (4.5x104 N/C, away)

B) Halfway between a 6.0 ?C and a -8.0 ?C charge, which are 10.0 m apart. (5040 N/C towards -8 ?C*)

C) 1.0 m from the end of a 3.5 m long uniformly charged rod, which has a 4.0 nC net charge. (8.00 N/C away from rod)

Two 1.20-m long, uniformly charged wires are perpendicular to each other, as shown below: + 2Q . P -Q

A) If Q = 2.5 ?C, find the electric field at point

An ideal monatomic gas expands adiabatically from an initial temperature of 384 K and volume of 4.6 m³ to a final volume of 10 m³. If the initial pressure is 1.5 ? P_atm, how much work is done on the gas?

A grappling hook is fired from a cannon at ground level with an initial speed of 40 m/s at an angle of 50 degree above the ground. It is a fired at a vertical cliff. The cliff is very high and we are very close. So we are sure that the hook will hit the face of the cliff.

1. Determine the x component of the initial velocity, and how that the y-component of the initial velocity is 30.6 m/s up.

1. It takes 4.0 second for the hook to hit the well. Determine the height of the hook at the point it hits the well and the y-component of the velocity at the time of impact.

1. Draw a graph of the y-component of the velocity vy as a function of the time for those 4.0 second the axes should be labeled, include units, and be to an appropriate scale.

1. Discuss the types of energy transformations that are involved in the following devices or events. (For example, for (a) striking a match transforms the chemical energy in the match head into thermal (heat) and radiant (light) energy).

a. striking a match

b. windmill

c. microphone

d. flashlight

e. water behind a dam flowing past a turbine to generate electricity