Question

in forward bias how the current will flow i dont understad ?

and why in the reversed bias the current does not flow ?

Answer 1

Forward Bias
When the battery is connected to a semiconductor device in such a way that the positive terminal of the battery is connected to the P type and the negative terminal of the battery is connected to the N type region. Then the current flows due to the electrons through a forward-biased PN junction.
Reverse Bias
When the positive terminal of the battery is connected to the N type and the negative terminal of the battery is connected to the P type region.
The direction of external voltage applied in reverse bias is opposite to that of external voltage applied in forward bias.
In a reverse-biased PN junction, current is blocked but only to the extent that the reverse bias voltage is less than the peak inverse voltage rating of the diode. A very small current flows due to to what are called minority carrier holes and electrons.