25.1
Capacitors and Capacitance
A device consisting of two electrical conductors that are separated by a distance and used to store electrical charges is called a capacitor. The spac…
Consider a solar light, which charges during the day and glows at night. Here, the capacitor stores the electrical charges.
The simplest capacitor consists of two parallel conducting plates separated by a vacuum.
When connected to a battery, electrons from the negative pole accumulate on the capacitor plate connected to it, developing a negative charge, while the other plate becomes positively charged.
A potential difference that equals the product of the electric field and the distance between the plates is generated across the plates until it reaches the battery voltage. The electric field is proportional to the charge and the surface area of the parallel plates.
Charged capacitors get discharged when connected to a load, and the electrons flow in the reverse direction untill the potential reaches zero.
The quantity of charge stored in a capacitor to create a given potential difference is capacitance, measured in farad units.
The capacitance for a parallel plate capacitor is directly proportional to the plate area and inversely proportional to the distance between the plates.
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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.