A wire connected to a bulb does not glow, whereas the filament of the bulb glows when the same current flows through them.Why?

When does a bulb glow ?

A solenoid with an iron core and a bulb are connected to a d.c. source. How does the brightness of the bulb change, when the iron core is removed from the solenoid?

Why does current flow in acids?

The filament of a bulb glows when current flows through it but the wires connected to it do not. Explain.