# Solve U1=U*R2/(R1+R2): Current Circuit Theory

• Lindsayyyy
In summary, the conversation discusses how to show that U1=U*R2/(R1+R2). The solution involves finding the fall of voltage at U1, which is equal to R2*I. The current does not split at this point because the point where U1 is measured is not attached to anything. This is a voltage divider, and the currents and voltages will change when something is attached.
Lindsayyyy

## Homework Statement

I want so show that U1=U*R2/(R1+R2) (sorry latex didn't work for me right now, don't know why)

## The Attempt at a Solution

I know the solution but I don't understand one step:
The solution says the following: the fall of voltage at U1 = R2*I (I is the current which comes from U). Why is that? Thats doesn't make sense to me, because I thought the current "splits" at this spot so I have: I=I1+I2.
Why does the solution say it's U=R2*I

Thanks for the help

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well u is the emf of the source right ?
but what is this ---------u1 ? wat's U1

I don't know how to describe it properly in english, but I think it's the voltage which drains off. I think the english term is voltage divider. But as I'am writing this I think I oversaw something.
The resistances are in series so the current is everywhere the same. Is this the right solution for the problem?

That's because the current does not really split.
The point where U1 is measured is not attached to anything, so no current flows.

This is indeed *only* a voltage divider.
Of course, when something (significant) is attached, the currents and voltages will change.

Ok, I didn't recognize that I have to handle it this way. Thanks for the help

## 1. What is the purpose of the equation U1=U*R2/(R1+R2) in current circuit theory?

The equation U1=U*R2/(R1+R2) is used to calculate the voltage drop across a series circuit. It is based on Ohm's Law, which states that the voltage drop (U) is equal to the current (I) multiplied by the resistance (R) of the circuit. In this equation, U1 represents the voltage drop across one particular resistor (R2), while R1 and R2 represent the values of the resistors in the circuit.

## 2. How is the equation U1=U*R2/(R1+R2) derived?

The equation U1=U*R2/(R1+R2) is derived from the series circuit rule, which states that the total voltage in a series circuit is equal to the sum of the individual voltage drops across each component. By rearranging the equation to solve for U1, we can calculate the voltage drop across a specific resistor in the circuit.

## 3. Is the equation U1=U*R2/(R1+R2) applicable to all types of circuits?

Yes, the equation U1=U*R2/(R1+R2) is applicable to all types of series circuits. It does not take into account any external factors, such as temperature or non-ohmic behavior, but it is a fundamental equation in current circuit theory.

## 4. How can I use the equation U1=U*R2/(R1+R2) in practical applications?

The equation U1=U*R2/(R1+R2) can be used to determine the voltage drop across a specific resistor in a circuit, which is important for understanding the behavior and performance of the circuit. It can also be used to calculate the total resistance of a series circuit, as well as the current flowing through each resistor.

## 5. Are there any limitations to using the equation U1=U*R2/(R1+R2) in current circuit theory?

While the equation U1=U*R2/(R1+R2) is useful in many cases, it does have limitations. It assumes that the resistors in the circuit are connected in series and that they have a constant resistance. It also does not account for any potential external factors that may affect the circuit's behavior.

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