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# P3 - Electricity Help? watch

1. I don't really understand the whole concept of current, potential difference, resistance, volts and amps and all the units and it's proving difficult to understand the rest of the topic without getting these - can anyone help????
2. location of curent, pd, resistance in this eg : metal wire

think about the sea of delocalised electrons and the positive cations present. Those delocalized electrons are moving at different directions although they are held by mettalic bond.When you apply a force to the charges (voltage from battery), the charges(thats a huge number of electrons in our example), they repel from cathode and move toward anode. Through the journey they bump into big cations.

current : rate of flow of charge Or in other words the amount of charges flown per second. thus its formula Q/t

pd : difference in work done per charge while passing through a component. for eg: Each charge carries some electrical energy before reaching a bulb in the circuit. The electrical energy is tranferred into light energy in the bulb. Work done is energy transferred. After passing the bulb the charges lost their energy. The difference of their energy before reaching bulb and after passing through bulb is potential difference.

I usually think about the pizza delivery analogy.
The delivey man brings in pizza from the shop ( cell).
Delivery man represents(charges).
On the way to the party house, he carries pizza (represets charges with energy)
He reaches the party house and delivers the pizza. (work done= energy transferred)
He leaves the party house without the pizza to the shop (charges without energy)

Resistance : measure of how difficult it is for charges to flow

As I said earlier its not clear cut for the charges to flow in the circuit. they bump onto the big cations as well. Remember the charges carry electrical energy (electric kinetic energy). When the charges bump onto the cations, they transfer the energy they have ie KE to cations.

What do the cations do? They absorb the energy and vibrate. These postive cations are like big mufos so when they vibrate, they sort of block the charges so reducing the speed of the flow of our poor charges.

in good electrical conductors, their cations vibrate at a low level at given temperature so speed of charges is more hence current is high
in good electrical insulators, their cations vibrate a lot, this increases the temperature. When temp increases, the cations get even more energy to vibrate and so the speed of charge flow decreases. Hence resistance increase and current decreases. (remember this concept is for ohmic resistors)
3. volts is the unit of voltage
amps unit for current
ohms unit for resistance

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