An up quark in a hadron changes to a down quark.
The elementary charge is \(e\).
What is the magnitude of the change in the charge of the hadron?
Correct Answer: \( \boxed{\mathrm{C}} \)
An up quark has charge \(+\dfrac{2}{3}e\), while a down quark has charge \(-\dfrac{1}{3}e\).
The change in charge is
\(\left|-\dfrac{1}{3}e-\dfrac{2}{3}e\right|=e\).
Therefore, the correct answer is (C).
The number of electrons in a neutral atom of an isotope of plutonium, \( ^{239}_{94}\mathrm{Pu} \), is changed to produce a charged atom (ion) \( W \).
\( W \) has an overall charge of \( +1.6\times10^{-19}\,\mathrm{C} \).
How many protons, neutrons and electrons are in \( W \)?
| protons | neutrons | electrons | |
|---|---|---|---|
| A | 94 | 145 | 93 |
| B | 94 | 145 | 95 |
| C | 238 | 94 | 239 |
| D | 239 | 94 | 238 |
Correct Answer: \( \boxed{\mathrm{A}} \)
Plutonium has atomic number \( 94 \), so it contains \( 94 \) protons.
The number of neutrons is
\( 239-94=145 \).
A charge of \( +1.6\times10^{-19}\,\mathrm{C} \) is equal to \( +e \), meaning one electron has been removed.
Hence the ion has \( 93 \) electrons.
Therefore, the correct answer is (A).
Which particle is a lepton?
Correct Answer: \( \boxed{\mathrm{B}} \)
Leptons are fundamental particles that do not experience the strong nuclear interaction.
The positron is the antiparticle of the electron and is classified as a lepton.
A meson is made of a quark and an antiquark, a proton is a baryon made of three quarks, and a quark is not itself a lepton.
Therefore, the correct answer is (B).
