Why do we use a transformer in AC circuits?

Why do we sweat ?

Why do we use a mirror with the coil?

Why do we use simple machines?

Why do wi use fuse in household circuit ?

Why do we use ball-bearings?

Suppose we have a transformer which converts 220 V AC to 12 AC. In the transformer when we apply 220 V DC voltage then usually coil is burned. Why ?

What is the use of choke coil in AC circuit? Can we use a rheostat in place of choke coil for the same purpose?