1. Intro to Physics Units

In physics, a location in space that has no size or dimension is called a:

What is the total kinetic energy of the decay products when an upsilon particle at rest decays to $r^{+}+r^{-}$?

Which of the following is the basis of the current standard for the $meter$?

A forward-bias voltage of $15.0$ mV produces a positive current of $9.25$ mA through a $p-n$ junction at $300$ K. What does the positive current become if the forward-bias voltage is reduced to $10.0$ mV?

In household wiring, copper wire with a diameter of $2.05\mathrm{mm}$ is often used. What is the cross-sectional area of such a wire in $\mathrm{mm}{2}^2$ (square millimeters)?

A proton and an antiproton annihilate, producing two photons. Find the energy, frequency, and wavelength of each photon if the $p$ and $\bar{p}$ are initially at rest.

Why Are We Bombarded by Muons? Muons are unstable subatomic particles that decay to electrons with a mean lifetime of 2.2 μs. They are produced when cosmic rays bombard the upper atmosphere about 10 km above the earth's surface, and they travel very close to the speed of light. The problem we want to address is why we see any of them at the earth's surface. (a) What is the greatest distance a muon could travel during its 2.2 μs lifetime? (b) According to your answer in part (a), it would seem that muons could never make it to the ground. But the 2.2 μs lifetime is measured in the frame of the muon, and muons are moving very fast. At a speed of 0.999c, what is the mean lifetime of a muon as measured by an observer at rest on the earth? How far would the muon travel in this time? Does this result explain why we find muons in cosmic rays? (c) From the point of view of the muon, it still lives for only 2.2 μs, so how does it make it to the ground? What is the thickness of the 10 km of atmosphere through which the muon must travel, as measured by the muon? Is it now clear how the muon is able to reach the ground?

A hydrogen atom in a particular orbital angular momentum state is found to have $j$ quantum numbers $\frac{7}{2}$ and $\frac{9}{2}$. If $n=5$, what is the energy difference between the $j=\frac{7}{2}$ and $j=\frac{9}{2}$ levels?

During each of these processes, a photon of light is given up. In each process, what wavelength of light is given up, and in what part of the electromagnetic spectrum is that wavelength? A molecule decreases its vibrational energy by $0.198$ eV.

What particle (a particle, electron, or positron) is emitted in the following radioactive decays?

(a) ${}_{14}^{27}Si{\to }_{13}^{27}Al$

(b) ${}_{92}^{238}U{\to }_{90}^{234}Th$

(c) ${}_{33}^{74}As{\to }_{34}^{74}Se$

The photoelectric threshold wavelength of a tungsten surface is $272$ nm. Calculate the maximum kinetic energy of the electrons ejected from this tungsten surface by ultraviolet radiation of frequency $1.45\times {10}^{15}$ Hz. Express the answer in electron volts.

Which statement is accurate about $mass$ or $weight$?

Which statement best describes the $m$eter as a unit of measurement?

Write out the following numbers in full with the correct number of zeros: 2.5 x 10⁻¹

Astronomers often detect radio waves with wavelengths of 3,000,000,000 nm. What is this wavelength expressed in decameters (dam)?