Why is the current same after and before passing through a resistor? •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
 A: 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..
A: 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. 
A: 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. 
