What is a resistor? & relationship between current and resistor?

Question

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firstly, do resistors "resist" current in a closed circuit? what is the resistor's actual function?

secondly, when you want to calculate the potential difference across a resistor, you use the formula V=IR. hence, it can be said that the current is constant at any point in the circuit. but if the current is "resisted" by a resistor, how can the current be the same throughout the whole circuit? take for instance the image (url above). why is the current that passes through resistors 1 & 2 the same?

Answer 1

A resistor is a device that exhibits a constant relationship between the voltage across its terminals and the current passing through. Resistance (R) is the mathematical inverse of conductance (G), that is, R = 1/G. All materials except superconductors exhibit some resistance, even ordinary wires; but the resistance in a wire is very low and can thus usually be considered zero.

The current around a loop of circuit must be the same, since there are no places in which charge can accumulate and current is the flow of charge over time. Thus, if R1 and R2 had different currents, then charge would have to be building up or dissipating between them, and clearly there is no way for that to happen according to the lumped-matter discipline of circuit design.

Instead, the applied voltage from the voltage source (battery) is divided up depending on the values of the two resistors in series, in such a way that Ohm's Law is maintained. If the two resistances have equal values, for example, the voltage across both resistors is the full applied voltage and the voltage between their midpoints and either end of the pair of resistors is one-half of the applied voltage. That's why resistors in series are called voltage dividers.

The combined resistance of multiple resistors in series is the sum of their individual resistances. Applying V=IR=I(R1+R2) and rearranging to I=V/(R1+R2) will tell you the total current through the circuit. Then, taking the total current, you can calculate the voltage across the two resistors with V1=I R1 and V2 = I R2. You will notice that V = V1 + V2.

Answer 2

resistors obviously resist in a closed circuit.Their function is in their name,to resist current flow.As in a series circuit the total resistance

is assumed to be parted across the whole circuit,current is considered

to be same all over it.At any series circuit current is same all over the circuit(through every element).It is assumed in this way.

You can't calculate the exact value,as the conductors(wires used to pass cuurent) have also some resistance.

To have a clearer idea you need to read any standard text book.

Hope you'll find.  

Answer 3

A resistor is a passive element in a circuit. It is usually made of carbon packed in a little tube. It has a certain fixed resistance to current flow. Example: A 10ohm resistor in series with another 10ohm resistor in a circuit with a 10 volt battery applied - The current flowing through each resistor is 10v/(10+10)ohms = .5amps. The voltage drop across each resistor is 10ohms x .5amps = 5v.

To your original question, a resistor indeed resists the flow of current. But in practice and circuit design, a resistor is usually inserted to provide a voltage drop for some other device.

Answer 4

Resistor do not 'resist' current, in the way you had imagined.

Imagine that you are in a car, the street 'resist' the car, (if not the car would be seeking under the pavement), but when you run the car you could get even more speed if the car could fly, but the 'resistant' in the tires, let get you a little speed less.

In a electrical circuit things are almost the same. You have a source of power, (a battery, or the electrical plug). How much 'current' could you obtain from that source at once. The amount of current will depends on all the resistors the circuit has. More resistors will give you less current (speed), les resistors, give you more current. That's why equation is  I = V/R.

To calculate the potential difference in a resistor, yor must carefully realize the difference between serial circuit and parallel circuit. That different is specially hard for rockies.

In a serial circuit you have only one current, and potential 'falls' in each resistor. In a parallel circuit, potential is the same for all the 'branch' and there are different current for each resistors.

Please refers to a good book in order to practice and understand serial and parallel current behavior

Answer 5

Resistors reduce the voltage of the current that flows from one part of a circuit to the next, maintaining a known safe current within one or more electrical components.

If the resistance of a material remains constant over a wide range of voltage, Ohm's law, I = V/R, applies and can be used to predict the behavior of the material. This applies to both DC and AC applications.

The resistors in your example are connected in series, so there is nowhere else for current to flow other than through the resistors. If one were 2 Ω and the other 4 Ω, the voltage drop across the 4 Ω resistor would be twice that of the 2 Ω resistor, but the current would be the same.

For example, if the battery were 6 V, the current would be 1 amp, and the voltage drop across the 2 Ω resistor would be 2 V, and that across the 4 Ω resistor would be 4 V.