gracy
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How to recognize output voltage?I thought it is Voltage across last resistance/capacitor.
What is the Potential Difference Between c and d in This Circuit?
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It is normally given in the problem itself.. However, the the terms input and output are commonly used in "systems" rather than in circuits like this. For example, power supply in our houses is Vin, the appliances connected to it are called 'load' and voltage across load is called output voltage.gracy said:
Here, R2 is the load.gracy said:
gracy
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Did not understand.
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Gracy, what names you give to variables is not so important so long as you define them, are consistent in their use, and they convey some idea of what they are meant to represent. This just boils down to naming conventions for quantities. You can choose any variable names you want if you are so inclined, so long as you define them for your audience, usually by showing them on the circuit diagram.
It is typical to use ##V## for voltages, ##I## for currents, ##R## for resistances, and so on, and to give them subscripts or suffixes to distinguish them. Input or source voltages are often labelled ##V_i## or ##V_s## or ##V_o## (meaning "original" or initial value). What you want to take as an output voltage for whatever purposes you have at the time can be labelled any way you want, but common choices include ##V_{out}##, ##V_o## (Yes, it can be used for both input or output labels, just not both at the same time!). Some people prefer to use U instead of V for voltages. It's a cultural thing. It should not cause confusion because variables should ALWAYS be defined before they are used!
Sometimes you want to reference a voltage across a particular component and then you might find it convenient to use, for example ##V_{R1}## or ##V_{C3}## where R1 and R3 are labelled components in your circuit diagram.
It's up to you to define your variables and labels for a given problem. If you are writing equations using variables then you should know what they represent beforehand because you have defined them. If you want to call the potential across any component the "output" of your circuit, that's entirely up to you. There is no strict rule about where that component has to be located in the circuit diagram (although most prefer to read circuit diagrams from left to right, top to bottom, input towards output. It's just a convention, and not a strict rule).
Above you presented a derivation for the voltage across a particular resistor in a voltage divider. You used variables R1, R2, Rtot, I, Vs and Vo. Each was clear in its use and intent, and you defined mathematically that Vo = I × R2 and correctly presented the finished expression. Yet now you are coming back to ask what the variables mean, and how to recognize the output? This doesn't make sense: You defined and used them yourself.
You can extend the voltage divider from two to any number of resistors and choose the potential across anyone of them to be your "output".
It is typical to use ##V## for voltages, ##I## for currents, ##R## for resistances, and so on, and to give them subscripts or suffixes to distinguish them. Input or source voltages are often labelled ##V_i## or ##V_s## or ##V_o## (meaning "original" or initial value). What you want to take as an output voltage for whatever purposes you have at the time can be labelled any way you want, but common choices include ##V_{out}##, ##V_o## (Yes, it can be used for both input or output labels, just not both at the same time!). Some people prefer to use U instead of V for voltages. It's a cultural thing. It should not cause confusion because variables should ALWAYS be defined before they are used!
Sometimes you want to reference a voltage across a particular component and then you might find it convenient to use, for example ##V_{R1}## or ##V_{C3}## where R1 and R3 are labelled components in your circuit diagram.
It's up to you to define your variables and labels for a given problem. If you are writing equations using variables then you should know what they represent beforehand because you have defined them. If you want to call the potential across any component the "output" of your circuit, that's entirely up to you. There is no strict rule about where that component has to be located in the circuit diagram (although most prefer to read circuit diagrams from left to right, top to bottom, input towards output. It's just a convention, and not a strict rule).
Above you presented a derivation for the voltage across a particular resistor in a voltage divider. You used variables R1, R2, Rtot, I, Vs and Vo. Each was clear in its use and intent, and you defined mathematically that Vo = I × R2 and correctly presented the finished expression. Yet now you are coming back to ask what the variables mean, and how to recognize the output? This doesn't make sense: You defined and used them yourself.
You can extend the voltage divider from two to any number of resistors and choose the potential across anyone of them to be your "output".
gracy
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Actually I copied it .gneill said:
gracy
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I want to understand what the formula means how to use it
on the left side there is voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
on the left side there is voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
Last edited:
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This formula is applicable only for resistors and not capacitors. I mean, you can't simply replace R1 with C1 and R2 with C2.gracy said:I want to understand what the formula means how to use it
at the left side there will be voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
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Right. For resistors and inductors.gracy said:I want to understand what the formula means how to use it
at the left side there will be voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
Mentor
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Refer to the derivation that you copied. The derivation used the fact that all the resistors in a series string share the same current. Then Ohm's law can be used with that current to find the voltage across anyone of the resistors in the string. It happened to be R2 in this example.gracy said:I want to understand what the formula means how to use it
at the left side there will be voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
So in the case of resistors, since the common factor for all the resistors in a string is the shared current you determined that current first. That's ##I = V_{in}/R_{eff}##, where I choose this time to name the total resistance ##R_{eff}##, or the effective resistance of the string. You could call it ##R_{tot}## if you want. Then Ohm's law tells you the voltage across any resistor in the string by multiplying the current by that resistor value.
$$V_{Rj} = V_{in} \frac{R_j}{R_{eff}}$$
Now, what is the common factor shared by all capacitors in a series string?
gracy
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Capacitors in Series all have the same current flowing through themgneill said:
gracy
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Please tell me am I correct in#68 that
Here in the following equation
on the left side there is voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
Here in the following equation
on the left side there is voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
Homework Helper
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Correct for resistors and inductors and not capacitors, as I said in #70.gracy said:Please tell me am I correct in#68 that
Here in the following equation
on the left side there is voltage across the numerator on right side.
V in is always the emf of source
and denominator on the right side would be sum of all the component(resistance or capacitor) present.
numerator on the right side is always the component (resistance or capacitor) across which we want to find the voltage i.e V present on left side.
gracy
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The equivalent charge is the same as the individual charges.cnh1995 said:
gracy
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Now how to proceed from here?
Mentor
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This is why it's better to understand the concept rather than try to memorize individual formulas. The concept applies to any number components in series, and a correct formula can be written down every time from the principle involved.cnh1995 said:
- Find out what is common to every component
- Calculate that common thing
- Apply the common thing's value to the individual component that you're interest in
gracy
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chargegneill said:
gracy
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100 multiplied by 8μCcnh1995 said:
800 μC=Qtotal
Right?
gracy
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100 multiplied by 2μC
200 μC=Qtotal
Right?
200 μC=Qtotal
Right?
gracy
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Vcd=200 μC/6μFcnh1995 said:
=100/3 Volts
Right?
