I was just wondering what happens in a circuit in terms of different types of energy transformations.
You can think of this just like gravity. See below.
If you apply a voltage to a circuit then electrons start moving (very slowly).
Voltage is a name for electrical potential difference.
- There is a gravitational potential energy difference between the floor and a higher shelf, because a book wants to fall down, if it could.
- There is an electrical potential energy difference between two points in a circuit, if the charge wants to move to another point.
But the electrons are also now moving once the voltage is applied as there is a current so would they have kinetic energy as well?
- A book falling from a high shelf is trading the gravitational potential energy into kinetic energy.
- A charge moving because a voltage is suddenly applied, is trading the electrical potential energy into kinetic energy.
Some information I have found online says that electrons collide with atoms in a bulb and this is why the filament heats up. But this would imply that kinetic energy is being transformed into heat [...]
- Drop a steel ball into a fluid, and the fluid resistance because of viscosity (because of "bumbing" into many water particles) with pull out some of the kinetic energy, slowing it down. This kinetic energy loss is indeed converted into heat.
- A charge "bumbing" into atoms similarly are slowed down, and the loss in kinetic energy is converted into heat.
[...] and this can't be correct because surely any change in kinetic energy would alter the current flowing?
It does alter the current flowing. Without the resistance, the current would be much, much higher.
- The steel ball falling through the water is slowed down and soon reaches a constant speed (terminal speed).
- The charge moving through a resisting material is slowed down and soon reaches a new equilibrium speed, where the "push" that makes it move (the voltage) balances out the resistance that holds it back.
The end-result is indeed a slower flow, i.e. a lower current, than without this resistor present (in that particular part of the circuit).
Also, in a series circuit, if you measure the potential difference between any 2 points after all of the loads then you always get zero. I was just wondering why it is zero because don't the electrons keep moving even after passing through all the load in order to get back to the power source so surely they cannot do this without some form of energy?
Remember Newton's 1st law. If charges exit the last resistor, they are no longer slowed further down, no. But the speed they came out with will stay. If nothing prevents them along the wire alone, they will not speed up, no, but also not slow down. So they continue.
And should one be stopped by whatever reason, the next charge will come and push it forward (like-charges repel). This is the case when the wire is not a completely perfect conductor but has a little resistance.