# Have i done this right Bndpass filter ?

#### Antony 16171

Joined Apr 7, 2021
11
Question: Measure V0 and Vi over the range of frequencies 1 kHz to 100 kHz
spec:
L=25mH
C=0.01uF
R=100 Ohms
Voltage source=10V

I've done , and am 90% sure ive done it wrong .

1
2pie/0.025*10^-3*0.01*10^-6

#### Papabravo

Joined Feb 24, 2006
17,020
Question: Measure V0 and Vi over the range of frequencies 1 kHz to 100 kHz
spec:
L=25mH
C=0.01uF
R=100 Ohms
Voltage source=10V

I've done , and am 90% sure ive done it wrong .

1
2pie/0.025*10^-3*0.01*10^-6
Without a schematic we can't tell what the expression is referring to. You mention a bandpass filter, but that does not tell us how the components are connected and it makes a difference.
What are you thinking?

#### Antony 16171

Joined Apr 7, 2021
11
Without a schematic we can't tell what the expression is referring to. You mention a bandpass filter, but that does not tell us how the components are connected and it makes a difference.
What are you thinking?

#### Papabravo

Joined Feb 24, 2006
17,020
OK, that's better. So the L and the C form a series resonant circuit. The resonant frequency occurs when the reactances of the inductor and capacitor are equal. This means that:
$2\pi fL\;=\;(2\pi fC)^{-1}$
$(2\pi f)^2\;=\;\frac{1}{LC}$
$f\;=\;\frac{1}{2\pi\sqrt{LC}}$
To evaluate the resonant frequency
$\frac{1}{2 \cdot 3.14159 \cdot \sqrt{25 \times 10^{-3} \cdot 0.01 \times 10^{-6} }}\;=\;10.07 \times 10^{3}$
Unfortunately that doesn't tell you much about the relationship between Vo and Vi over the indicated frequency range. How would you proceed?
How about making a table of impedance values for the L and the C so you can compare them to the load resistor of 100 Ω