| English | 意味 |
|---|---|
| charge/tʃɑːdʒ/ | 電荷 |
| Coulomb's law/ˈkuːlɒmz lɔː/ | クーロンの法則 |
| coulomb/ˈkuːlɒm/ | クーロン |
Rub a balloon on your hair — now it sticks to the wall
- Rub a balloon on your hair and it clings to a wall, defying gravity.
- Rubbing moved invisible charge 电荷 from one surface to the other.
- Charges come in two kinds, and they push and pull without ever touching.
- The rule for that push and pull is Coulomb's law 库仑定律.
Two kinds of charge
- There are positive and negative charges (protons are +, electrons are −).
- Like charges repel; opposite charges attract — the fundamental rule.
- Charge is measured in coulombs 库仑 ($\text{C}$); the electron's charge is tiny.
- An object is charged when it has unequal numbers of protons and electrons.
2つの負の電荷が互いに近い位置に置かれています。これらは:
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同種電荷は反発し、負の電荷同士は互いに押し合う。
電気的電荷の単位は ____ 。
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電荷の単位はクーロン（$\text{C}$ ）である。
正の電荷と負の電荷が互いに近接した場合、どうなるか:
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異種電荷は引き合う。
Coulomb's law
- The force between two point charges is $F = \dfrac{k q_1 q_2}{r^2}$.
- It grows with each charge and falls off as the inverse square of the distance.
- Double the distance and the force drops to a quarter — just like gravity.
- $k$ is Coulomb's constant; the direction is along the line joining the charges.
電荷の場
電荷を変化させ、それ自身が周囲に作る電界を確認してください。
2つの電荷を $2\ \text{m}$ の距離から $1\ \text{m}$ の距離まで近づけたとき、力は何倍になるか？
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$r$を半分にすると、$1/r^2$が$4$倍になる——力は4倍となる。
2つの電荷間の静電力を増加させる変化をすべて選択せよ。
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$F = kq_1q_2/r^2$ はいずれかの電荷の大きさと近さに応じて増加する。離れると弱まる。
Just like gravity, but stronger
- Coulomb's law has the same inverse-square shape as gravity.
- But the electric force is vastly stronger and can repel as well as attract.
- Gravity only ever pulls; the electric force does both, depending on the signs.
- This is why chemistry and electronics are governed by electric forces, not gravity.
重力と同様に、静电力も距離の逆二乗則に従う。
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両方 $F = kq_1q_2/r^2$ と重力は $1/r^2$ に比例するが、静電力には引力だけでなく反発力もある。
Coulomb's law is inverse-square ($1/r^2$), not $1/r$. Doubling the separation quarters the force, not halves it. And remember the force can be a push or a pull depending on whether the charges are alike or opposite.
Two charges are moved from $2\ \text{m}$ apart to $1\ \text{m}$ apart. How does the force change?
- Halving $r$ multiplies $\dfrac{1}{r^2}$ by $4$.
- The force becomes four times stronger.
There are two kinds of charge (+ and −): like repel, opposite attract. Coulomb's law gives the force, $F = \dfrac{kq_1q_2}{r^2}$ — an inverse-square law like gravity, but far stronger and able to both attract and repel.