Power source for Arduino Board using wall plug or wall charger

Using Arduino IDE 1.x
1

Is it possible to power on my arduino uno using a wall plug, my wall plug's rating are Input: 240VAC, 0.5A
Output: 4v, 1500mA.

2

No, get a 5V adapter.

(If you want to augment your credentials as a developer, you may want to look up how to specify a URL)