Electric Circuits and Current Flow

A Battery stores chemical energy and uses it to separate charges and counteract the electrostatic forces of repulsion against like charges, this creates a potential difference between terminals as V=kq/r, as q is negative for the electrons, this creates an electric field around the cell/battery. However, this electric field is not uniform to the wires of the circuit In an electric field, electrons following it will hit the walls of the conductor due to the field lines being slightly angled to make a full loop, therefore there will be a component that is parallel to the wire and one perpendicular to it. Charges will re-distribute and move towards the surface, nearer the site of the perpendicular force to pose an opposing field that cancels out the perpendicular force/ field. As F=qE. Therefore other electrons will only experience the parallel force from the electric field. At this point, the net electric field traces the circuit. Current in the circuit stays constant because there will be an electron build up near the mouth of a resistor due to electrons colliding with atoms inside the resistor more often, therefore losing velocity. This means that other electrons will collide with those inside the resistor and therefore be accumulated near the mouth of the resistor. This creates an area of negative charge around it. The area of negative charge effectively generates electrostatic forces of repulsion to repel electrons in the resistor, making them travel faster and therefore inducing higher current and also reduces the current coming into the mouth because of the electrostatic force of repulsion again. As more charge accumulate, this effect is going to increase until the electrostatic force of repulsion is so high that charges now move through the resistor the same speed as it is taken in to the mouth of the resistor, because I=Q/t, the same velocity of electron transfer = the same current. The more resistance a component holds, the more charge build up it holds and therefore there will be a very high electric field strength at the area is going to be very high compared to the outing of it, and because V=Ed, the difference in electric field strength creates potential differences proportional to it’s resistance. In a series circuit, the voltage divides because there is no alternative path for charge redistribution so when electrons build up at a resistor in series, so electrons have to “endure” the high electrostatic force of repulsion in a very high electrostatic field strength and out of it, creating a difference in electric potential. In a parallel circuit, the potential difference across branches stay constant because the electric field re-distributes charges (If a branch has higher potential difference, electrons will be repelled to go into the branch so more flows towards the other branch). The reason why current differs from branches is because when potential differences is equal across branches (due to charge redistribution), branches with higher resistance need more electron build up to maintain the same current flow (So same charge accumulation). However, lower resistance paths allow electrons to flow more easily with less accumulation, so current flows that way. V=IR. Drift velocity = net motion from electric field – resistance from collisions, it stays constant because when in resistors of high resistance, the electrostatic forces of repulsion gives it a larger electrical field strength but that also increases collisions, so drift velocity stays constant throughout the whole circuit, and because drift velocity is directly proportional to current, current stays constant in a series circuit. Sources : https://courses.lumenlearning.com/suny-physics/chapter/19-1-electric-potential-energy-potential-difference/ https://spark.iop.org/electric-current-flow-charge https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/what-are-series-and-parallel-circuits/ https://www.savemyexams.com/a-level/physics/edexcel/17/revision-notes/3-electric-circuits/resistance-resistivity--potential-dividers/3-11-current--drift-velocity/ https://users.wpi.edu/~physics/ph1120b11/Images/1120Lec09Current&Resistivity.pdf https://www.physicsclassroom.com/class/circuits/Lesson-2/Electric-Current https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/07:_Electric_Potential/7.03:_Electric_Potential_and_Potential_Difference