# Help understanding current through series circuit

by Kaldanis
Tags: circuit, current, series
 P: 106 This isn't a specific homework question, it's just something I'm having trouble understanding or visualising. Take this L.E.D. circuit for example, which works according to our textbook: The current flows from the - to the +, so clockwise in this circuit. To me, it looks like the current would leave the battery and 12V would flow straight to the LED light and melt it before it gets a chance to reach the resistor. So based on that, I'd think that this circuit wouldn't work... but I also know that current is equal at all points in a series circuit, so the resistor must have affected the current before it reaches the LED? If I worked it out right then the resistor has 10.5V and 52.5Ω. I don't understand how it can take 10.5V and lower the current if the LED is before it in the circuit, can someone please explain this? I'm sure I'm just thinking about it the wrong way! 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution
 HW Helper Thanks P: 10,768 First: the current flows out from the positive terminal of the battery and in at the negative one, so it is anti-clockwise in the circuit shown. Do not visualize the current as a car, reaching at different points of the circuit at different times. It is more similar to a long train all round the loop. When the engine starts, it pulls the first carriage, but as soon it starts to move, it pulls the next one and so on... practically, the whole train starts to move at the same time. When you switch on a battery, the electrons near the negative pole of the battery are pushed away and get closer to the electrons farther away and push them, those will push the electrons in front of them and so on, round the loop to the positive pole where the excess electrons are absorbed by the battery. Meanwhile new electrons enter at the negative pole, so the electron density does not change in time , only "the push" travels along the circuit: The potential difference between the terminals sets up an electric field in the loop almost without time delay: it is the electromagnetic field that travels, not the electrons, they are set into motion by the electric field.The current is the same at every point of a series circuit. In the LED, there is mechanism at the pn junction which allows a certain current and voltage to set up. Do not worry about it, just use the given data. ehild
P: 106
 Quote by ehild First: the current flows out from the positive terminal of the battery and in at the negative one, so it is anti-clockwise in the circuit shown. Do not visualize the current as a car, reaching at different points of the circuit at different times. It is more similar to a long train all round the loop. When the engine starts, it pulls the first carriage, but as soon it starts to move, it pulls the next one and so on... practically, the whole train starts to move at the same time. When you switch on a battery, the electrons near the negative pole of the battery are pushed away and get closer to the electrons farther away and push them, those will push the electrons in front of them and so on, round the loop to the positive pole where the excess electrons are absorbed by the battery. Meanwhile new electrons enter at the negative pole, so the electron density does not change in time , only "the push" travels along the circuit: The potential difference between the terminals sets up an electric field in the loop almost without time delay: it is the electromagnetic field that travels, not the electrons, they are set into motion by the electric field.The current is the same at every point of a series circuit. In the LED, there is mechanism at the pn junction which allows a certain current and voltage to set up. Do not worry about it, just use the given data. ehild