Hello everyone...!!!! i have made different logic gates using 7402 ic (quad 2-input nor gate ic). what actually occurs is that after joining different gates for making "and" gate & "or" gate until i give the input the LED glows( i have connected the negative terminal of LED to negative terminal of battery and the output of final nor gate to the positive terminal of battery). But before giving high or low input on any of these gate (i.e. 0 volts in the input terminals), the bulb glows, but as soon as i connect low voltage source (i.e. 0 input) the bulb doesn't glows(which should happen).. so i didn't found it why the LED was glowing when i didn't gave any input. Can anyone please help?????