Difference of terms help.

[paulmdrdo]

please help. what does it mean when they say "voltage across" some component. and how is "voltage aross" different from "voltage drop"? I'm confused please help!

 

[jpanhalt]

From a common reference:

Volt (or Volts): Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 volt will push 1 ampere of current through a 1-ohm resistive load.

So, voltage is always the difference in potential between two points. "Voltage drop" has the added implication of current flow (https://en.wikipedia.org/wiki/Voltage_drop). Thus, one may use the term "voltage drop" when referring to the voltage across a resistor versus simply "voltage across" a capacitor or insulator. However, it is not incorrect to refer to the voltage "across" a resistor.

Why is the distinction important to you?

John

 

[paulmdrdo]

it's because I cant answer this problem.



isn't that the voltage across a diode is always 0.7v? but I don't know how to determine if the diode here is forward bias or reverse.

 

[FvM]

That's no problem of terms, it's about understanding electrical circuits.

The diode voltage won't be "always 0.7 V", it's only in forward bias, in other words when the circuit is driving a current through the diode.

The solution is using two steps.
1. Calulate the voltages without a diode.
2. Decision. If the diode voltage is > 0.7, you have forward bias, recalculate the voltages and currents. If it's < 0.7 no diode current, use the solution from step 1.

 

[paulmdrdo]

what do you mean by calculate the voltages? the sources are given? please bear with me. :?:

 

[FvM]

In forward bias, the diode has to be replaced by 0.7 V voltage source. You are right, the voltages are all determined, you need to calculate the currents.

 

[paulmdrdo]

how would I calculate the current? what method should I use?