# tough question

#### mamodt

Joined Nov 6, 2004
1
Dear folks,

I was asked to find the transmittance using the given parameters: R1,R2,C1,C2 and w, and find the cases in which the transmittance doesn't depend on w.

This is an AC circuit, but first of all, I dont understand how the capactiors play a role in the transmittance x.x

I thought:

T = R1/(R1+R2)

even when this circuit is AC.

help would be appreciated.

#### arvind

Joined Nov 4, 2004
18
what is transmittance by the way. sorry for my ignorance but plz tell me
thnx

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

Yes, transmittance leaves me wondering, too. It looks like you're trying to determine the voltage across R2.

The only case where w is not a factor is when the applied voltage is DC. With AC applied, the capacitors become reactive, where Xc = 1/wc. That makes both capacitors appera as if they were resistive elements in parallel with the resistors.

For two resistors in parallel, the product of the resistances over the sum of the resistances will give the equivalent resistance. Use Xc as the value of one resistor, and you get the answer.