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### Course: Class 12 Physics (India)>Unit 2

Lesson 9: Capacitance & parallel plate capacitors

# Capacitors and capacitance

Capacitors, essential components in electronics, store charge between two pieces of metal separated by an insulator. This video explains how capacitors work, the concept of capacitance, and how varying physical characteristics can alter a capacitor's ability to store chargeBy David Santo Pietro. . Created by David SantoPietro.

## Want to join the conversation?

• why the electric potential is high near positive charges ?
• Electric potential at a point near a charger is measured in terms of the work done(by an external) agent in bringing an unit positive charge from infinity to that point. Clearly to bring an unit +'ve charge from infinity to a point near a positive charge would be more than the work done to bring the unit positive charge from infinity to an identical point near a negative charge since in the former case the agent would have to overcome a repulsive force which opposes the bringing of the charge..while in the latter case the attractive force helps in brining the unit +'ve charge
• sir u said that two metal pieces store same amount of charge independent of sizes. but capacitance is dependent on area. then how can it be possible.suppose if two pieces of different areas are taken then what will happen?
• I think the smallest plate limits the total charge, so regardless of the size of the larger plate
it has no impact on the capacitance of the capacitor.
Ideally each plate is the same area, to make use of materials.
• If you removed the salt bridge in a galvanic cell, would it hold the charge like a capacitor?
Or would the charges just equilibrate?
• Ideally, it should hold charge like any other system and it should pretty much act like a capacitor if the distance is not very great. Wait for an expert to answer on this topic.
• i have really simple question...
why need capacitor??
why do we need to store charge?
what could possibly go wrong if there is no capacitor??
plz tell me i want to explain to my future student
• Capacitors are used in TVs and this allows them to instantly turn on, they are also used in defibrillators.
• Why exactly is electric potential lower at where the negative charges are than at where the positive charges are? If the electric potential is the amount of work which will be used or gained per charge for or from moving an amount of charge, why would it matter if the charge creating the field is positive or negative?
• It takes positive work to move a positive test charge closer to a positive charge, so that means the electric potential energy is positive. Likewise it takes negative work to move a positive test change closer to a negative charge, so the electric potential energy around negative charge is negative. Electric potential (voltage) is a measure of the electric potential energy per unit charge, so if the electric potential energy is negative, the voltage will also be negative.
• Does the charge just travel through the air then? How does the current continue to flow through the entire circuit when a capacitor is in it?
• The circuit isn't actually complete, but there is still a push for the electrons to move, because the plates of a capacitor represent free, open space for them to distribute along.
• how potential difference is developed when positively charged pate and negatively charged plates are separated?(exact reasoning )
• The potential difference is simply the work that has to be done to bring a unit charge from one terminal to the other. This is also the case for a battery, there is a potential difference across the two terminals, because near the negative terminal there is a lower electric potential than at the positive terminal. Think of it as the free electrons really want to go to the positive side, but can't, as in the case of a battery, but as soon as there is a closed circuit the electrons will move to the positive terminal. So the potential difference, or the voltage, is simply a measure of how much work has to be done, to get from one point to the other, or how much of this work is stored in the separate electrons, which want to go back to the positive side.
If this doesn't make much sense, think of when you are lifting a book. You had to do work to overcome the force of gravity. As soon as you release that book, it will fall towards the ground. The work that you had to put in to lift the book, and which is now stored in the book, is analogous to the potential difference.
• @ the video states that eventually electrons become attracted to the positive piece of metal - what dictates this occurrence? Is it only once both ends of the capacitor have reached an equal magnitude of charge?
• Thats a great question.

The electrons are ALWAYS ATTRACTED BACK TOWARDS THE POSITIVE PLATE.
However, they can continue to be moved from the positive plate onto the negative plate for as long as the voltage from the battery is LARGER than the voltage between the negative and positive plate.
When the voltage between the plates is equal to the voltage of the battery, no more lelectrons can be drawn from the positive plate.