Note taking!

[AirLandBus]

Hey guys,
Im currently doing prelim 1/2 physics and doing pretty well overall (<90%). My question is, im really struggling condensing the info in the textbook down. Some of my notes for one section of the chapter can be up to 3 - 4 pages (2 sheets) long, and i struggle finding the most important, from the stuff that is relevant and helps my understanding that i should still remember from the stuff thats total rubbish. Any tips/advice?

Can someone provide a sample of this section condensed?
In a battery, or cell as we should say, the source of EMF is the chemical energy stored in the materials used. As we saw at the beginning of the last chapter, atoms have varying abilities to attract electrons—chemists call it electronegativity. A cell basically consists of two materials with different electronegativities, between which there is what we shall call a 'go-between' material.

The chemistry of electrical cells can be very complex, but for our purpose it is sufficient to realise that electrons will flow from the material of lower electronegativity (for example zinc) to the one of higher electronegativity (for example copper) through the external circuit connected to the terminals.

In the diagram material A has the highest tendency to attract electrons and material C the lowest. Material B acts as the 'go-between'. It is effectively a conducting material that allows the other two materials to 'trade' electrons by undergoing a chemical reaction with each of them which either replaces the electrons lost (material C) or takes up the electrons gained (material A). In the course of this process the positive and negative ions in material B migrate towards A and C respectively. As a result of these reactions, material B is eventually used up and the product of the reactions replaces it. At this stage the cell stops working and we say it has gone 'flat'.

The properties of the materials chosen for A, B and C are very important. Materials A and C must have as different electronegativities as possible but also undergo suitable reactions with material B. Material B must allow the migration of the ions (charged atoms) formed in the reaction and so is normally a liquid or a moist paste. In a dry cell, C is the outer zinc casing, and B is a paste of ammonium chloride and other special substances (see Figure 2.22). Material A is not actually a metal but manganese dioxide powder, which is mixed with the ammonium chloride paste. The carbon rod in the centre of the cell is there to collect the current. In a charged car battery, A is lead dioxide coated on a lead plate, B is a solution of sulfuric acid and C is a lead plate. As current from the car battery is used, lead from the lead plate is converted into lead sulfate, which remains as a coating on the plate. The lead dioxide is also converted into lead sulfate, which remains on the other plate. Fortunately this process can be reversed by forcing an electric current through the battery in the opposite direction, and so the battery can be recharged. This is one of the functions of the car's alternator.

There are many other types of cells in use. Some are single use and some (so-called 'Ni-Cads' for example) can be recharged. There is now considerable incentive for manufacturers to develop smaller, more efficient rechargeable batteries for use in electric cars and portable electronic devices.

Thanks.

[AirLandBus]

Bumppp

[silverpixeli]

Is this your notes, or an extract from a textbook?

I'd like to help but I've never studied that part of a physics course if it is part of one (There's nothing on how batteries work in year 12 physics, though there may be some section of the year 11 course that covers it but the internal working and the makeup of a battery isn't part of the study design for units 3/4)

Could you give me something from motion/electronics?

[AirLandBus]

Is this your notes, or an extract from a textbook?

I'd like to help but I've never studied that part of a physics course if it is part of one (There's nothing on how batteries work in year 12 physics, though there may be some section of the year 11 course that covers it but the internal working and the makeup of a battery isn't part of the study design for units 3/4)

Could you give me something from motion/electronics?

Extract from textbook. Units 1 and 2 from Hienemann.

In order to drive a current around an electric circuit the charges must be given energy. A battery or generator is the usual source of this energy. Another increasingly common source of electrical energy is the photovoltaic cell, or solar cell. These devices are all referred to as sources of EMF. The letters stand for ElectroMotive Force, but that is an inaccurate term because the EMF involves the energy given to the charges rather than the force on them.

In order to understand the meaning of an EMF it is helpful to consider another source of EMF, the Van de Graaff machine (see Figure 2.4). The source of energy in this case is very obvious. The motor is pushing the charges on the rubber belt up against the electrostatic repulsion of the charges already on the dome. The more charge already on the dome, the greater the force, and hence the greater the work that has to be done to bring more charge to the dome. In fact, you may hear the motor slow down as the concentration of charge on the dome builds up.

In many ways the EMF can be visualised as a 'concentration of charge'. The more charges put on the dome, the more concentrated they become and the greater the force of repulsion between them. The work done pushing the charges together (by the motor in this case) is stored as electrical potential energy.

Just as the compressed spring in a jack-in-the-box contains potential energy, so do all the 'concentrated' charges. And just as the spring energy can be recovered when it is allowed to expand, so the electrical energy can be recovered when the charges are allowed to fly apart again. When a spark flies from the Van de Graaff generator we see the result. The potential energy is rapidly converted into kinetic energy, and as the charges collide with the air molecules it is turned into heat, light and sound energy.

EMF is defined as the amount of work done for each unit of charge in this process of charge concentration. Because it is, therefore, actually the 'electric potential energy per unit charge', this quantity is most often abbreviated simply to electric potential or just potential. The EMF is then the electric potential given to charges by the device. A battery uses chemical potential energy to give the charges in the circuit this potential energy. A generator uses the kinetic energy of rotation, and solar cells use the energy in sunlight.

[silverpixeli]

In order to drive a current around an electric circuit the charges must be given energy. A battery or generator is the usual source of this energy. Another increasingly common source of electrical energy is the photovoltaic cell, or solar cell. These devices are all referred to as sources of EMF. The letters stand for ElectroMotive Force, but that is an inaccurate term because the EMF involves the energy given to the charges rather than the force on them.
import takeaway here is just the following:
To drive current around a circuit you need a source of EMF (misnomer: actually energy)
Sources include batteries, solar cells

In order to understand the meaning of an EMF it is helpful to consider another source of EMF, the Van de Graaff machine (see Figure 2.4). The source of energy in this case is very obvious. The motor is pushing the charges on the rubber belt up against the electrostatic repulsion of the charges already on the dome. The more charge already on the dome, the greater the force, and hence the greater the work that has to be done to bring more charge to the dome. In fact, you may hear the motor slow down as the concentration of charge on the dome builds up.
don't generally need to copy examples into notes unless they're particularly helpful for you, the idea of an example like this is that you visualise it in your head while reading and that helps you visualise the rest of the stuff. this particular example is pretty unhelpful, to me anyway, because in a circuit you don't have a 'buildup of charge on a dome' it just flows round and round and the cell gives it the energy to go round again, or at least you can think of it like that

In many ways the EMF can be visualised as a 'concentration of charge'. The more charges put on the dome, the more concentrated they become and the greater the force of repulsion between them. The work done pushing the charges together (by the motor in this case) is stored as electrical potential energy.
more example via van de graaffs that doesnt exactly relate to circuits, but we're starting to see that emf is actually about giving charges potential energy

Just as the compressed spring in a jack-in-the-box contains potential energy, so do all the 'concentrated' charges. And just as the spring energy can be recovered when it is allowed to expand, so the electrical energy can be recovered when the charges are allowed to fly apart again. When a spark flies from the Van de Graaff generator we see the result. The potential energy is rapidly converted into kinetic energy, and as the charges collide with the air molecules it is turned into heat, light and sound energy.
cool, this all makes sense, but it's not stuff you need to memorise. what you should takeaway is that a source of emf gives charges potential energy, and they are free to spend that potential energy, say, by going around a circuit

EMF is defined as the amount of work done for each unit of charge in this process of charge concentration. Because it is, therefore, actually the 'electric potential energy per unit charge', this quantity is most often abbreviated simply to electric potential or just potential. The EMF is then the electric potential given to charges by the device. A battery uses chemical potential energy to give the charges in the circuit this potential energy. A generator uses the kinetic energy of rotation, and solar cells use the energy in sunlight.
we can add generators to our list of emf sources we made after the first paragraph
we can also add the definition that emf = energy / charge and this is called potential
(note something that took me till first year physics to pick up, potential is energy per charge, potential energy is all the energy on however many charges you're talking about, this is a subtlety that was never made explicit to me haha)

unfortunately, the knowledge of what is important and what isnt important really required a pretty in depth understanding of everything going on. it's often only after learning about a topic that i can go back and make these sorts of decisions.

making notes as you're first discovering a topic is really hard for these reasons, sometimes it's better to try a few questions open book to get a feel for how to apply the concepts and you'll start to notice what's important/worth noting down for ease of reference

as a general rule, examples are for illustrative purposes and like, it's no easier having an example drawn out in your notes than having it in the textbook, which you can always refer back to if necessary.

hopefully that helps?