Question about Voltage and Current

[mguptamel]

After reading texts, I am confused with Voltage and Current. As per Ohms law, V = IR.

When texts explain for a given circuit, they always talk in terms of voltage not current especially V(out) in case of voltage divider. Why is that? I get confused at this point.

Please see attached diagram

For Leg1 and Leg2, output voltage will be the same but current going through output will be very different. If, for example, output needing high current would work from LEG2 but not LEG1.

Can somebody explain when OUTPUT (Vout) is considered in a given circuit does that mean it's an output to 2nd stage and designers must consider voltage instead of current?

 

[chuckey]

Generally voltage is the independent variable, you change the voltage and the current then changes, however its value is set by the circuit resistance. For instance you can change the battery voltage in your little circuit and the currents then change.
In your circuit, let the voltage from the battery be V volts then the current flowing down leg1 will be V/(1k + 1K) = V/2K so the voltage drop across the bottom resistor (V=IR) will be (V/2K) X 1K = V/2. looking at leg2, I = V/ ( 10K +100) = V/10100. the voltage drop across the output resistor = (V/10100) X 100 , V = V/101 or roughly V/100.
Frank

 

[Tahmid]

Usually a voltage divider is designed to divide the voltage. You may have the same voltage output from different divider circuits. But they will have different currents depending on the divider resistances.

For Leg1 and Leg2, output voltage will be the same but current going through output will be very different. If, for example, output needing high current would work from LEG2 but not LEG1.

Current going through output will depend on resistance of the output. This resistance will be parallel to one of the divider resistors. So, the overall resistance will change and hence output voltage will change. So, it's important to draw small current so that the output voltage is not affected.

Can somebody explain when OUTPUT (Vout) is considered in a given circuit does that mean it's an output to 2nd stage and designers must consider voltage instead of current?

Yes, it's an output to a further stage where voltage, instead of current, is considered.

Maybe, this will help clear doubts: **broken link removed**

Hope this helps.
Tahmid.

 

[jtrent]

You have to understand that with Ohm's law as V = IR
You can also use it as I = V/R and R = V/I

So for any part of your circuit, if you have two known values, you can find the other.

 

[Syncopator]

A voltage divider is much easier to understand if you consider its equivalent circuit.

An example is shown below.

 

[hshah8970]

The others over here have already done a good job of explaining why the focus is voltage over current. I would like to add another reason to the list, in terms of signals and data:

In terms of signals and data, the voltage of a signal represents its strength whereas the current represents its speed. While analyzing a system, we focus on voltage because we want to compare a signal's entering strength with its exiting strength. When we are talking about individual devices, voltage across each end of the device will almost always be different but the current magnitudes on both sides will be the same. Thus it makes more sense to focus on voltage rather than on current while explaining circuits in books.

However designers do not focus only on the voltage. They compute each and every thing in their circuit and consider voltage, current, resistance, capacitance, and inductance - everything is considered.

I hope that helped.

Humza.