To Establish Truth Tables for AND, OR and NOT Gates Apparatus AND,OR and NOT gates, two photodiodes, LED, battery
Procedure Set up circuit as illustrated in Fig 24.25. Current will only flow through the photodiodes when exposed to light, the LED will emit light when current flows through it.
Expose both photodiodes A and B to light. Note whether the LED lights.
Expose photodiode A to light and cover B. Note whether the LED lights.
Cover photodiode A and expose B to light. Note whether the LED lights. Cover both photodiodes A and B. Note whether the LED lights.
Observation The truth table for the AND gate is established.
Note Truth tables for OR and NOT gates can be found with the same approach using the circuits in Fig 24.26 below.
A B
C AC
A B
C
Fig 24.25: Circuit diagram to establish truth tables for an AND gate
(a)
(b) Fig 24.26: Circuit diagrams to establish truth tables for (a) an OR gate and (b) a NOT gate
‘SECTION B’ SHORT QUESTION
Typical of Question 5 in Leaving Cert. Exam
Q1 Answer all of the following parts (a), (b), (c), etc. (a) Give one contribution made to physics by Nicholas Callan.
(b) Transformers usually have a soft iron laminated core.What is the purpose of the soft iron core and why is it laminated?
(c) Draw the truth table for a NOT gate.
(d) How can a galvanometer be converted into an ohmmeter? (e) Draw the basic structure of a bi-polar transistor.
