A radio frequency choke is air cored whereas an audio frequency

choke is iron-cored Give reason for this difference.

 We know, 

Reactance of an inductor, X_L  = ω L = 2πf (μ_oμ_rn²lA)

Using the above expression,

For radio frequency (high frequency) the reactance will be large even for μ_r =1. That is why radio frequency choke is air cored.  

For audio frequency (low frequency) the reactance will be small if  μ_r =1. So to increase the reactance an iron core is inserted (μ_r is large) that is why the audio frequency choke is iron cored. 

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