# Why is the current same after and before passing through a resistor? [closed]

•Why is the current same after and before passing through the resistor ? •Why is a voltage drop across the resistor ?

Explanation in terms of electron flow and electric field will be really helpful.

Thanks

• Electricity is mostly just plumbing--at least for the newcomer. Current is flow (gallons per second), EMF (voltage) is pressure, and resistance is a restriction (imagine cotton crammed into a pipe--water still flows through it, albeit slowly). There are even analogies for capacitance and inductance. Feb 26 '19 at 15:55
• Possible duplicate of Why is current the same in a series circuit? Feb 26 '19 at 16:46
• If you roll some bowling balls down a hill, the bowling balls loses gravitational potential energy. But you still have the same number of balls at the bottom of the hill as you set loose at the top of the hill. Feb 26 '19 at 17:13

Resistor opposes current in the circuit. I too had this problem when I was a new comer than I got this!!

When current flows through the resistor then speed of electrons (which actually is current) slows down. Now there is potential across the resistor drops this drop is due to the fact that the energy needs to be maintained of electrons and potential is used up to increase the kinetic energy (that is current ) to it's previous value.

Thus current remains constant and potential drops.

Note: This is just to understand and is may not actually what happens.

Hope that helps..😊

Now guys it’s important it understand what current is. An electric current is actually the amount of charge passing through a given cross-sectional area of a conductor per second(in a unit time ). Now think of your resistor as a piece of pipe. When you insert a given amount of water in one end the same amount of water must come out the other end. Assuming of course that your pipe has no leaks. It’s the same with current. What goes in must come out. It’s just the Kirchhoff law simplified infinite times. What does the resistor do? Well it opposes the flow of current. Consider that you take pneumatic tube and connect it to a water outlet. Then you squeeze the pipe in the middle. Now you are opposing the flow of water. It’s the same thing a resistor does.

Electric current is the flow of charges through a conductive wire. Charge is conserved, so any unit of charge flowing into one end of the wire must be accompanied by the departure of the same amount of charge flowing out of the other end of the wire. This means current in = current out.

A resistor is an imperfect conductor, which means current cannot flow through it effortlessly. The effort required to push the charges through the resistor is supplied by voltage. Work expended per unit of time is equal to effort x flow which in this case is voltage x current, or watts.

So, as we traverse the length of a resistor, the voltage at the current-in end diminishes until the current-out end is reached, at which point the voltage (but not the charge nor the current) has been dissipated away to zero. The resistor has converted the electrical power flowing into it into thermal power flowing out of it.

• so.. when going through the resistor the current drops, right? since mapping it with the water analogy, amount of water flowing through squeezed pipe is less. Also to push through the resistance if more force is required, i.e. voltage, then why is its valued dropped instead of rise? Aug 25 at 13:44
• @azima, no that is wrong. remember: charge is conserved in a resistor. charge flowing in = charge flowing out. To push through the resistance: note that for a voltage source, connecting it to a resistor cuts down on the current while the input voltage stays the same. For a current source (which is rare), connecting it to a resistor increases the voltage so the current stays the same. In all of these "Ohm's law" problems a voltage source is assumed! Aug 25 at 16:56
• so we are assuming voltage source here? and the voltage stays the same resulting in current drop? Aug 27 at 15:55
• no... the source voltage is constant. a voltage drop occurs across the resistor. Aug 27 at 19:07