The RL series circuit may be used as a first order filter. Depending on the chosen output to be in the the inductor or resistor, it may behave as a high pass (HP) or a low pass (LP) filter.

When the output is in the inductor, the transfer function is:

                                  H(s)_{PA} = \frac{s}{s + \frac{R}{L}}

a) Examine the Bode Diagram of this high pass filter when the values of the resistor and of the inductor vary.

R =  Ω     L =  H

Frequency from  to  Hz

When the output is in the resistor, the transfer function is:

                                  H(s)_{PB} = \frac{\frac{R}{L}}{s + \frac{R}{L}}

b) Examine the Bode Diagram of this low pass filter when the values of the resistor and of the inductor vary.

R =  Ω     L =  H

Frequency of  to 

An interesting exercise is to compute the responses of both filters using the same values of R and L, and then compare results.