Can you take multiple courses at once?

[ineedhelpnow]

when is the LED on for the circuit shown? (Construct a truth table) btw that part that's cut off at the top says 5 V but i don't think the voltage or resistance matters in this problem. how many low and how many high inputs do i need to get that LED to light up?

View attachment 3279

 

[ineedhelpnow]

my drawing is a little off. it's supposed to be a NOR gate.

 

[ineedhelpnow]

i found the answer to this question to be "The LED will be on when any of the four inputs are HIGH." nor operation produces a low when any of the inputs are high and high when both inputs are low. i would figure that you need a high for the LED to light up so therefor don't the inputs have to be low?

---------------------------------------------------

oh i understand now. its because in order for a system to maintain stability you need high and low voltage so you can't have 1111 or 0000 therefor it has to be when any of the inputs is one even if it means an output of 0.

 

[I like Serena]

i found the answer to this question to be "The LED will be on when any of the four inputs are HIGH." nor operation produces a low when any of the inputs are high and high when both inputs are low. i would figure that you need a high for the LED to light up so therefor don't the inputs have to be low?

For the LED to light up, the voltage just above the LED must be high, and the voltage just below the LED must be low.
Otherwise, current wouldn't flow.
Therefore, the output of the NOR must be low.

Btw, the part of the sentence that says "(nor operation produces) a high when both inputs are low" should really read: "(nor operation produces) a high when all inputs are low".

oh i understand now. its because in order for a system to maintain stability you need high and low voltage so you can't have 1111 or 0000 therefor it has to be when any of the inputs is one even if it means an output of 0.

Nope. That's not it.

 

[ineedhelpnow]

ok how about. a 0 is needed to stabilize the voltage of 5V...
but then why does 0000 not work? that produces a low also.

 

[I like Serena]

ok how about. a 0 is needed to stabilize the voltage of 5V...
but then why does 0000 not work? that produces a low also.

Logic gates like the NOR have no need for stabilization.

Consider what 0000 means.
It means that all inputs count as "false".
What is:

NOT ( false OR false OR false OR false )

 

[ineedhelpnow]

oh i figured the whole thing as a device need to be stable.
false OR false OR false OR false (this part really confused me )

 

[I like Serena]

oh i figured the whole thing as a device need to be stable.

A logic gate like this one is considered stable by definition.

false OR false OR false OR false (this part really confused me )

This is about logic.

Suppose I want to know if you want to take a (any) course.
And suppose to do so, I ask you if you want to take

course A or course B or course C or course D

If you don't want to take any of them, the answer is no (aka false).
But if you want to take 1 or more of them, the answer is yes (aka true).