Two relays each with 20 ohms resistance and 0.16 henry inductance are connected in series. What is the equivalent impedance?

Would't frequency matter?

No frequency given

Z=40+j2*(2PI*f*.16)

so not knowing f, equivalent impedance is difficult to put a number on.

What if the frequency is 30hertz?

Where did u get the 40 in the impedance?

if f=30, put that in, calculate Z. You can write it in polar form, if you are familiar with that. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/impcom.html

The real part 40 represents two 20 ohm resistors.

I don't know how to get

Rectangular form

Given:

F = 60 Hz (selected).
R = 20+20 = 40 Ohms.
L = 0.16+0.16 = 0.32 henry.

Z = R + jXl = R + jWL.
Z = 40 + j377*0.32,
Z = 40 + j120.64 = 127.1 Ohms.

Note: W = 2pi*F = 377 at 60Hz.

Z = 40 + j120.64 = 127.1 Ohms[71.6o].

Tan A = 120.64/40 = 3.016,
A = 71.6o.