Why does having a high input impedance and low output impeda

[alexdr5398]

Homework Statement

Say you connect Circuit A with low output impedance to circuit B with high input impedance. Why does this cause minimal voltage drop compared to connecting them the other way around (high output to low input).

Homework Equations

P = V^2/R
P = IV

The Attempt at a Solution

I am guessing that the power must stay the same when going from circuit A to circuit B, so when the resistance increases, the voltage drops to keep the power equal. But why does this cause a "minimal" voltage drop. Wouldn't matching the impedance be the best way reduce the voltage drop?

 

[berkeman]

Homework Statement

Say you connect Circuit A with low output impedance to circuit B with high input impedance. Why does this cause minimal voltage drop compared to connecting them the other way around (high output to low input).

Homework Equations

P = V^2/R
P = IV

The Attempt at a Solution

I am guessing that the power must stay the same when going from circuit A to circuit B, so when the resistance increases, the voltage drops to keep the power equal. But why does this cause a "minimal" voltage drop. Wouldn't matching the impedance be the best way reduce the voltage drop?

Think about Vin and Vout. When the output resistance of a stage is high into a low-input impedance stage, what happens to the Vin seen by the 2nd stage? Think voltage dividers...

 

[alexdr5398]

Think about Vin and Vout. When the output resistance of a stage is high into a low-input impedance stage, what happens to the Vin seen by the 2nd stage? Think voltage dividers...

I've never learned about voltage dividers. Would the Vin in the 2nd stage be larger than the Vout in the 1st stage?

 

[scottdave]

Homework Equations

P = V^2/R
P = IV

The Attempt at a Solution

I am guessing that the power must stay the same when going from circuit A to circuit B, so when the resistance increases, the voltage drops to keep the power equal. But why does this cause a "minimal" voltage drop. Wouldn't matching the impedance be the best way reduce the voltage drop?

I think you are confusing maximum power transfer and minimum signal (voltage) loss.

 

[berkeman]

I've never learned about voltage dividers. Would the Vin in the 2nd stage be larger than the Vout in the 1st stage?

No, Google voltage divder circuits and do a little readng. You'll find that the Voltage Divider equaton is like this:

$$V_{out} = V_{in} \frac{R_d}{R_i + R_d}$$

Try that search, and try answering again.