why are sparks seen on electric pole if the wire become loose?
Loose wire means the connection is being opened and closed frequently.
When you open a circuit that has lots of inductance in it, like motors and transformers, the inductance will try to keep the current flowing. This results in very high voltages at the point where the connection opened. that high voltage just continues to climb until it is high enough to arc over the gap and cause conduction which continues the current. That arc is what you may see as a spark.
But all of this sparking and arcing heats up the wires at the point of contact, and bits of molten metal may be thrown away, and that can be seen as a spark also.