State the functions of the following parts of a D.C supply unit:

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 (I) Filter : 

     - used to remove the A.C component and allow only D.C component to reach the load from the rectified output.

(II) Transformer: 

      - It isolates the rectifier circuit from power line and thus reduces the risk of electric shock.

        - It allows us to step up or step down the A.C input voltage .

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