If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Physics archive>Unit 12

Lesson 1: Ohm's law and circuits with resistors

# Resistors in series

Explore the fundamentals of circuits and Ohm's law with a focus on series circuits. Discover how voltage remains constant between elements and how current remains constant throughout the circuit. Learn how resistors in series increase total resistance, and how to calculate current using Ohm's law. Created by Sal Khan.

## Want to join the conversation?

• Hey, I am curious if the battery would also drive the wire's electrons and cause the wire to be positively charged?
• The metal conductor does not get deprived of its electron, the electrons are passed from atom to atoms.
• How can the voltage be equal at both the points ()? In the previous video, Sal said that voltage is electric field times distance. Clearly, there is a difference in distance between the two points.
• Yeah that it is quite confusing, the way to think about voltage in a circuit is "work being done on charge".
In circuits we are assuming that the work to move a charge through a conducting wire is negligible compared to the work getting the electrons through the resistors.

Of course that isn't true, work is needed just to move the electrons through a wire even if it doesn't have any resistance but that amount of work is totally negligible.
• I didn't get it why electric current is a constant everywhere in a circuit if it is C/s, Sal said there is a Voltage(electric potential energy) drop after electrons went through resistor which i understand means that Force is less then the Force before electrons enters resistor, since W=V=Fd and distance d is a constant. Then this should imply that kinetic energy increases...and so more particles passes per second.....no something wrong, i am getting so confused, but even when Sal said particles slow down after passing resistor (obviously) means less particle goes per second, so where i am making logically mistake.....HELP PLS!
• imagine if this circuit were without resistor(but the wires can still have a resistance lets consider to be 1 ohm) and we consider the voltage to be 5v then the current must flow from the rate 5 amp but after we apply the 2 resistors lets say of 2 ohm each then the current will flow at 5/4 rate throughoutr the whole wire not only the resistors
• If the electrons are travlling the same speed through out the circuit how do they "know" to go at a slower speed if they might not bump into anything to slow them down?
• The thing is that resistors are just pieces of material that insulates really well so all the electrons will equally reduce their speed/voltage
(1 vote)
• How is the current is same at all places in series circuit when there are resisters?
• Basically it comes from conservation of charge. If there were portions of the circuit where more current was going in than going out, that would imply some net charge was building up in that region. We know this is not possible from Gauss's law, so the current must be the same throughout the same segment of a circuit. If a circuit splits into multiple nodes, then the incoming current will be split among those additional paths so only at that point will the current change.
• what is the physical reason for the voltage drop..? is it a 'buildup' of electrons on the entry-side of the resistor, so there is more energy pushing each one to move forward to the less-crowded side? and why does this make the voltage drop at all, why aren't the electrons still pushed just as much as before to get to the + terminal? o-o ..
• The electrons flow through the resistor without any of them actually stopping, but since work is done some of their energy is imparted as heat.
• Why is the current flowing from positive to negative? Surely if its a metal conductor then it would move from negative to positive because the metals de-localised negative electrons are attracted to the positive end?
• yes you are right

there are two ways to think about current (sorry to say)

The elctrons move, as you say, from negative to positive. Makes sense to us now but many years ago, before we knew about electron and its charge it was assumed that 'whatever flows, flows from + to -. This idea has been around so long that it continues today and we call it 'conventional' current

so, sorry to say it, you need to remember that electrons move in the opposit direction to conventional current....

hope that helps
• If the electrons are moving at a speed of "few centimeters per second",then how is it that when we press the switch of a bulb , it lights up instantly with in a fraction of second?
• That would probably be because electrons are everywhere in the circuit. When the switch is pressed the electrons closest to the bulb begin to move at the given speed and so the bulb lights up.....similarly followed by the other electrons in the circuit.
Please let me know if there's a better explanation!
• How the voltage is constant at every point when there is a voltage drops? And Sal said that the electrons become less eager after they bump into a resistor, doesn't that mean that the potential difference is decreased?
• what does a resistor do , does it only slow done the time by which an electron travels from point A to point B or it reduces the amount of current flowing in the circuit ?

Related to this is the next question that why is the amount of current flowing in a circuit same all throughout when resistors are connected in a series shouldn't the amount of current get reduced ?

please its a request to explain in as simple language as possible .