Understanding Electricity: The Basics of Current, Potential Difference, and Resistance

hi everyone so this is your first piece of home learning for physics um it's the basics of

electricity and basically we've set it because um a lot of this information you like to

write down and highlight and have your notes but it takes an awful long time to go

through and so we would like to spend the time with you in lesson and doing some model questions and

things which are a bit harder so it's really important that you from these slides

pause me every now and then write down what you want to write down and anything anything you don't understand from the

slides you can then talk to your teacher about okay so we're going to begin with

current so the definition of current and what it is

so current is the flow of charge through a substance such as a metal or a solution so in a wire current is

the flow of electrons and they have a negative charge in an ionic solution which is

something we you come across more in chemistry you have both negative

and positive charges and they both move okay in something like a proton beam protons

are positive so it's the positive protons which move at gcse physics you're going to be

mostly interested in the electrons now current is measured in a circuit with an ammeter which you would have

used before in year eight and its symbol is strangely an i and people always ask

me why is it an ion not a c well when um current was discovered and explained um the person who found it or discovered

it was french and so he called it intensity decorate

and so that's where the i comes from so the current is measured in amperes so that's the unit of the current

and ampere was the scientist who who discovered it it was talking about before we often say

amps for sure and the symbol for amps is a so if we're thinking about our literacy and how we would be talking

about current and an example is if you write down i equals 3a

such as i've done on this slide that is exactly the same as saying the current is three amps

so the i means current the three is obviously three and then the capital a is amps

how should we think about current then well a really handy model to imagine when you're thinking about current is

water thrown through a stream or a river so if you have a look at the image okay the

wires would act as the sides of the rivers so this these parts here and then the flow of

the water would be the flow of electrons through the wire

it's a really good analogy to use and when you're looking at a problem it's a really good way of thinking about

current but it doesn't work in every situation sometimes it doesn't help you think

about other aspects of electricity but if you're just thinking about current it's a really good place to start

okay we're now going to look at potential difference so potential difference is a measure of

the electrical energy being carried through the circuit by the charge

so the electrons how much energy basically are they carrying around the circuit

and when you're measuring potential difference in a circuit you're effectively measuring the difference

between the electrical energy at one point and the electrical energy at the other

point so for example that could be one side of a ball and then the other side of the bulb

you're measuring the difference in electrical energy between those points

and there is a difference because the bulb will use some of the energy so the difference in potential gives you

an idea of the amount of energy being used now it's not exactly energy because it's

not measured in joules but it's related to energy because it's how much energy there is per uh unit of

charge so it's about how many electrons there are and how much energy they're carrying and

we'll do that more in lesson because that's a little bit more difficult to understand so potential

difference is measured in a circuit with a voltmeter its symbol is capital v and as it's

sometimes referred to as voltage it's measured in volts and the symbol for volts

is v so a little bit easier to understand the current because both of the symbols are capital

v so if you're thinking about literacy and how you're going to say it if you saw written down

v equals 3v that's exactly the same as saying the potential difference across the bulb is three volts

okay so let's think of a model about how to think about potential difference

so you need to change your view of current in this so rather than thinking about

the water i want you to think of them as vans i know that sounds a bit weird but

they're a van okay and they're driving around a circuit now i want you to think about the cell

as or the battery as a bakery making loaves of bread okay so the cell of the battery is providing

the vans with bread and in this case we're going to think of the bread

as the electrical energy so their voltage okay so the cell or the battery provides

that so the set if it's a big cell it could provide really big loads

or if it was a small one it might provide smaller loads that's how we're going to think about it

now the vans get loaded up at the bakery with all the loaves so they have the potential to deliver

them okay so the loads of the voltage so when they get loaded up the bands have the

potential to deliver the loads when the vans then go out and deliver the loaves to the houses

around their circuit then they will then give their loaf to a house and then that house

then has some voltage or some energy but the van is now empty and it needs to go and get refilled

so if you measure the voltage before they deliver and after they deliver there is a difference

okay and therefore a potential difference and i've got an image to try and show that please

excuse crudeness of this because i couldn't make it animate properly so i'm just going to move it myself

so here's your bakery the bakery is going to load up the bread van with a loaf okay we're then going to

move the bread fan around the circuit with its loaf and then it gets to

the house at the house the bread van will deliver the loaf so it will give it to the house

it will now be empty and it needs to move background to the bakery to be filled up again

so there was a difference in the ability to deliver energy here because here it had the loaf and then

here it didn't have the loaf so there's a difference in potential

when it goes back around to the bakery the bakery will then give it some more bread and it has the

potential to deliver that voltage again if you're not sure about that because the central difference is a bit harder

to think about ask your teacher in your lesson the last couple of things i want to talk

about here then of resistance now we will do a lesson on resistance but just so you know

it links with current and potential difference so the resistance in a circuit forces

the electrons to give up their voltage so therefore creating a potential difference so what the resistance does

is as the electrons flow through it makes them give up their voltage so when the current flows through

something with the resistance the electrical energy is then converted into other forms e.g

in a light bulb that would be heat and light the light bulb forces the electrons to

give up their electrical energy and turns it into heat and line now the system for the symbol for resistance is

r and resistance is measured in ohms okay and the symbol for ohms i have not put on here so i just need to pause it

and i'll add it in okay so there we go i've added the ohm symbol so you can see it looks

like a head with little shoulders coming off okay so that's the symbol phones owns uh

resistance was discovered by a scientist called uh on our own and so that's his

symbol that he uses okay right the very last thing i want you to do then for this home learning

is um these are the circuit symbols so and open switch close switch cell so one what you would call a battery in

let's say like a remote control or whatever is actually called a cell so cells have

1.5 volts and one of them is called a cell if you have more than one then you call it battery

so you can see the cell and the battery symbols are really similar it's just that um if you drew two of

them that would mean two cells and this dotted line in the middle means more than two so you might put the

voltage above to show how many volts it is you need to make sure that there is a

long side and then a short side and then a long side and a short side so the long side is the positive side and

then the short side is the negative side we then have a diode which we will be doing about in another lesson learning

what it does a resistor a variable resistor a lamp a fuse a voltmeter an ammeter

thermistor and what's called an ldr which is a light dependent resistor you need to draw these symbols down and

you need to know them so that when you reuse them in lessons you know what they are okay as i've said

before any issues with any of what's been taught write down the information

in your book highlight it and then you can talk to your teacher about the bits that you didn't understand

thank you