27.1
起電力
起電力 (emf) は、電流を高いところから低いところに流す力です。 潜在的。 起電力はまったく力ではありませんが、「起電力」という用語は歴史的な理由から使用されています。
定電流を流す回路には、起電力発生源が含まれている必要があります。 EMF 源の例には、バッテリー、発電機、太陽電池、熱電対、燃…
バッテリーの発明者であるアレッサンドロ・ボルタは、起電力または起電力という用語を作り出しました。
EMFは力ではなく、バッテリーの2つの端子間の電位差です。
記号イプシロンで表されるEMFは、開回路でバッテリーが供給できる最大電圧です。ボルトの単位で表されます。
2つの端子の間にワイヤが接続されると、起電力は電子を負の端子から正の端子に押し出します。
EMFは、ユニットチャージをターミナル間で移動するために行われる作業量として定義されます。
閉回路では、バッテリーの端子間で測定される電圧は端子電圧として定義され、これは常にEMF値よりも小さくなります。これは、バッテリーの内部抵抗rがあるためです。
したがって、端子電圧は、その起電力と内部抵抗の両端の電圧降下との差です。
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Q1: Why is electromotive force called a force when it is not actually a force?
The term electromotive force is used for historical reasons, coined by Alessandro Volta, the inventor of the battery. Despite its name, emf is not a force but rather a potential difference between the two terminals of a battery. It represents the maximum voltage a battery can deliver in an open circuit, measured in volts.
Q2: What is the relationship between emf and terminal voltage in a battery?
Terminal voltage is the voltage measured across a battery's terminals when current flows through it, and it is always less than the emf. This difference occurs because the battery has internal resistance. Terminal voltage equals the emf minus the voltage drop across the internal resistance, which increases as the battery depletes.
Q3: How does a battery function as a charge pump in a circuit?
An emf source functions as a charge pump, moving negative charges from the positive terminal to the negative terminal to maintain the potential difference. Work must be done on these charges against the electric field, requiring energy from chemical reactions in the battery. This process raises the charges' potential energy and maintains the high potential at the positive terminal.
Q4: What are examples of devices that produce electromotive force?
Examples of emf sources include batteries, electric generators, solar cells, thermocouples, and fuel cells. All these sources transform energy of some kind—mechanical, chemical, thermal, or other forms—into electric potential energy and send it to the circuit. This energy transformation is essential for maintaining current flow in any circuit.
Q5: How is electromotive force defined in terms of work and charge?
Electromotive force is defined as the amount of work done to move a unit charge across the terminals of a battery. When there is no current flowing, the emf equals the work done on the charge per unit charge. Its unit is the volt, derived from joules of work divided by coulombs of charge.
Q6: What causes the internal resistance of a battery to increase over time?
Internal resistance generally increases as a battery is depleted due to oxidation of the plates or reduction of the acidity of the electrolyte. This increase in internal resistance causes a greater voltage drop across the battery's internal resistance, further reducing the terminal voltage available to the external circuit.
Q7: What happens to electron flow when a wire connects the terminals of a battery?
When a wire is connected between the two terminals, the emf pushes electrons from the negative terminal to the positive terminal through the external circuit. Simultaneously, the battery's internal charge pump moves negative charges from the positive terminal to the negative terminal internally, maintaining the potential difference needed for continuous current flow.