25.1
コンデンサと静電容量
一定距離離れた 2 つの導電体で構成され、電荷を蓄積するために使用されるデバイスはコンデンサと呼ばれます。 導体間の空間は真空か、誘電体と呼ばれる絶縁材料です。 コンデンサには、無線受信による静電気のフィルタリングから心臓除細動器のエネルギー貯蔵まで、さまざまな用途があります。
導体が 2 つの同一…
日中は充電され、夜に光るソーラーライトを考えてみましょう。ここでは、コンデンサが電荷を蓄えます。
最も単純なコンデンサは、真空で分離された2つの並列導電板で構成されています。
バッテリーに接続すると、負極からの電子が接続されたコンデンサプレートに蓄積して負の電荷が発生し、もう一方のプレートは正の電荷を帯びます。
電界とプレート間の距離の積に等しい電位差が、バッテリー電圧に達するまでプレート間で生成されます。電界は、平行プレートの電荷と表面積に比例します。
帯電したコンデンサは、負荷に接続すると放電され、電位がゼロになるまで電子が逆方向に流れます。
特定の電位差を生じさせるためにコンデンサに蓄積される電荷の量は、ファラド単位で測定される静電容量です。
平行プレートコンデンサの静電容量は、プレート面積に正比例し、プレート間の距離に反比例します。
View the full transcript and gain access to JoVE Core videos
Q1: How does a parallel plate capacitor store electrical charge?
A parallel plate capacitor consists of two conducting plates separated by a vacuum or insulating material. When connected to a battery, electrons accumulate on one plate, creating a negative charge, while the other plate becomes positively charged. A potential difference develops across the plates until it equals the battery voltage, allowing the capacitor to store electrical charge.
Q2: What is capacitance and how is it measured?
Capacitance is the quantity of charge a capacitor stores per unit of applied voltage. It is measured in farads (F), named after Michael Faraday, where one farad equals one coulomb per volt. Capacitance represents the ratio of maximum charge that can be stored to the applied voltage across the capacitor's plates.
Q3: How do plate area and distance affect capacitance?
Capacitance is directly proportional to the surface area of the parallel plates and inversely proportional to the distance between them. Increasing plate area increases the charge storage capacity, while decreasing the distance between plates strengthens the attraction of opposite charges, thereby increasing capacitance.
Q4: What happens when a charged capacitor is connected to a load?
When a charged capacitor connects to a load, it discharges as electrons flow in the reverse direction through the circuit. The potential difference across the plates decreases until it reaches zero, releasing the stored electrical energy to power the connected device.
Q5: How is the electric field related to charge in a parallel plate capacitor?
The electric field between parallel plates is directly proportional to both the charge stored and the surface charge density on the plates. Since surface charge density equals charge per unit area, the electric field magnitude increases with greater charge accumulation on the capacitor plates.
Q6: What role do dielectrics play in capacitor design?
A dielectric is an insulating material placed between capacitor plates to replace vacuum. Dielectrics enhance capacitance by allowing closer plate spacing and improving charge storage efficiency. Understanding dielectric properties like susceptibility, permittivity and dielectric constant helps optimize capacitor performance for specific applications.
Q7: What are practical applications of capacitors?
Capacitors have diverse applications including filtering static from radio reception and storing energy in medical devices like heart defibrillators. Solar lights use capacitors to store daytime electrical charge and release it at night, demonstrating how capacitors enable energy storage across many technological systems.