# Difficulty understanding electricity concepts

In circuit diagrams what does it mean for energy to be used in going through a component? I usually see this when emf is being described:

total energy supplied per coulomb by battery = total energy per coulomb used in load resistence + total energy per coulomb wasted in internal resistence.

What is "energy supplied by battery"? Where does this energy come from? How does it get supplied (for example, when a charge moves through the battery what exactly happens to that charge, does it get a "energy boost" from the battery or something?)

I also see it when for example potential difference is being defined: Potential difference across a component is 1V when you convert 1J of energy moving a charge of 1C through the component.

What does "convert 1J of energy" mean? What is doing the converting and what converts into what? Is it electricity converting to heat?

I would really appreciate detailed explanations for a layman, because I don't know much about electricity.

Thanks!

A negative charge attracts a positive charge and repels an also negative charge. If you have many (negative) electrons in one end of a wire and non in the other end, then these electrons will be pushed away from each other towards the end from which they are not pushed away. This principle is the key - the electron-dense end is called the negative end, the not-so electron-full end is the positive end (less negative is positive in this regard).

Think of energy in a circuit the same way as you think of energy because of gravity.

• Lift a book to a bookshelf, and there is more gravitational potential energy in this system. If the book is released (tilts off the shelf) this energy is being converted into kinetic energy as it falls.
• A charge in a negative wire-end is like the book on the bookshelf. If it is free to move, it will move. Towards the positive end. Therefor there is a electric potential energy in this system. The charge will "fall" towards a state over lower potential energy, that is it will "fall" to a positive potential. We call the total electric potential energy $\mathrm{[J]}$ devided with the amount of charge $\mathrm{[C]}$present at a wire end the electric potential $\mathrm{[J/C]}$. The negative end thus has a negative potential and the positive end a positive potential.

Therefore just as there is more gravitational potential energy present when the book is high up, and less when the book is closer to the ground, similarly there is more potential energy in a system when many negative charges are close together and have a positive area to go to.

The battery is what supplies the extra electrons at one end giving that end a negative potential.

In circuit diagrams what does it mean for energy to be used in going through a component?

"Energy used" means something like "energy converted". The moving charges have kinetic energy, which comes from the electric potential from when they were in the negative end. While they move away from that end that potential enegy is converted into kinetic energy. Just like the book falling from the bookshelf.

In a resistor, kinetic energy is converted into heat. In a light bulb, it is converted into light (and heat as a (usually) unwanted bi-product). In an electric engine, the energy is in the end converted into mechanical rotation.

What is "energy supplied by battery"?

As said, electrons want to move from negative to positive end. The battery brings them back! Takes them from positive to negative end, even though that is not a natural proces. This is like you picking up the book (from lower potential energy) and putting it on the shelf (back to high potential energy). The battery in this way adds energy to the system so that again charged a willing to move around.

Where does this energy come from?

As the energy to lift the book comes from your body, and before that from the food you eat, the battery contains an energy source which is used up while electrons are brought back up to the negative potential. Inside a usual battery you have chemical reactions freeing energy for this proces.

The emf you mentioned is the electric potential energy that the battery is able to move an amount of charge back through. The unit of emf is still $\mathrm{[J/C]}$; the amount of energy the battery can pull one coulomb of charge back through, or you can say: the amoun of potential energy the battery can give back to this system for every coulomb of charge.

Therefor the emf will be the difference between the two battery poles - at the positive end, there is low potential energy for the electrons, while at the negative end there is exactly the emf more potential energy.

How does it get supplied (for example, when a charge moves through the battery what exactly happens to that charge, does it get a "energy boost" from the battery or something?)

Yes, an energy boost is a fine way to see it.

What does "convert 1J of energy" mean?

Conversion of energy is just making into another form of any. $1 \mathrm{[J]}$ of electric potential energy can be converted into $1 \mathrm{[J]}$ of kinetic energy as the charge speed up, which can then be turned into $1 \mathrm{[J]}$ of heat later when it meets resistance.

What is doing the converting and what converts into what? Is it electricity converting to heat?

It depends on the conversion. As said earlier, there are many types of conversion (that is, conversions into many other types of energy; not just into heat.)

"Is it electricity converting to heat?" is not a good way to say it. Rather say "Is it electricit potential energy converting to heat?" and then the answer is "Yes." (if it is heat of course).