1.Why does transformer action can't take place in a dc circuit?2.on transformer coil what 5% tap means?
Transformer action is caused by the collapse in the primary field inducing a voltage in the secondary. A dc circuit will only generate a pulse when disconnecting it from the DC source.
A transformer is basically 2 inductors or coils usually wrapped around a ferious donut. When a DC voltage is applied to one side of the transformer the coil will charge like an inductor 230nsc1.phy-astr.gsu.edu/hbase/electric/indtra.html then it acts like a wire with some resistance value. When the DC voltage is removed the the current will want to continue flowing and will produce a voltage spice and colapse to 0 as the magnetic field collapses. When using a transformer in an AC circuit the current flip flops at the given frequency. The coil 'charges' in the primary winding building a magnetic field which expands past the secondary winding. When the voltage changes polarity the primary winding magnetic field collapses and rebuilds in reverse polarity. The rapid collapse causes the secondary winding to induce a current because when a magnetic field colapses though a conductor it induces a current. The colapse of the magnetic field is the key.
A 5% tap means that on the secondary coil there is a tap (a connection that leads out) 5% of the way up (or down) the coil.
