After watching this video, I decided to make the same circuit is there. The circuit has 2 NOR gates and makes 2 LEDs turn on and off. It is very similar to the one here:
I used 5V and 100 ohm resistors for my LEDs. For the resistors connected to the inputs of the NOR gates, I used 100 ohms and everything worked fine. But then I tried using 10k ohms and both of the LEDs were lit. I started varying resistor values and found out that 1k ohm works fine. I am confused why larger resistor values make both of the LEDs stay lit.
My NOR gate is 74LS02PC.
Here is my circuit: