# 15 - Past Paper Simulation - Boolean Logic (A)

1. Chelsea has taken up part-time lecturing whilst at university and an undergraduate's first question was regarding why it is an advantage to use as few gates as possible in a logic circuit. State the answer in a sentence (1 mark)

2. Ozan is unsure of how to complete the last row of this 'AND' gate truth table. Can you help him? What are the three values from left to right? (e.g. 0 0 1). Do not use commas in your answer. (3 marks) 3. Write the Boolean expression for B. Instead of the usual notation, use the actual names of gates in your answer (e.g. X XOR Y ?.or X AND OR Y) (1 mark) 4. A single output Q is produced from three inputs A, B and C. Output Q is required to be 1 only if inputs A and B are 1, or input C is 1 and input B is 0. Select the correct boolean equation: Option1, Option2 or Option3. (1 mark)
```Option 1
=========
Q = A.B . C+¬B

Option 2
=========
Q = A+B + C.¬B

Option 3
=========
Q = A.B + C.¬B```

5. Martin is working on a top secret CPU design using 'universal' gates and complex boolean circuitry. What logic gate does this truth table represent? (1 mark) 6. Syeda has a terrible headache after a long day's work and needs some help deciding the correct value for output Q (in the red box). It's either 0 or 1 - which one is it? (1 mark) 7. Maitreya stayed late at the electronics lab and has had a brainwave. Referring to the above circuit, two of the gates could be replaced by a single gate. Which two gates can be replaced? (2 marks)

8. Tanmay had an even more interesting insight. He realised a single gate could replace the two gates (referring the question above). Which single gate could be used? (1 mark)

9. Theft and burglary is on the rise. Chloe's company is designing an alarm system. The simplistic logic circuit is shown below. What is the Boolean expression for this circuit? Use "+" for OR, "." for AND, and "NOT" for NOT. (2 marks) 10. Brilliant engineer Agaash realies there is a small flaw in the current alarm system. If a burglar steps on to the mat and moves off it, or an open door is closed, the alarm stops ringing. What could be used to cause the alarm to keep ringing? (1 mark)
```Additional notes
=================
E = Sensor (outputs TRUE when door is open
and FALSE when shut)

N = Pressure mat (outputs TRUE when weight
detected, false when no weight detected)

L = This is a key that turns the alarm on and off.
This outputs TRUE when alarm is switched on and FALSE
when the alarm is off.

B =This is the alarm output. It is TRUE if:
1) The alarm is ON AND
2) either of the sensors E or N are set to TRUE```

11. The answer to the above question is something that will store the state of its input. In effect, it acts as _________. (1 mark)

12. Henry, Shusangar and Tharun are competing against each other in an interview for IBM's electronics division. First, they need to identify the logic circuit, its purpose and fill in the missing output for S. Write your answer below (3 marks) 13. Why is a D-Type flip flop referred to as a positive-edge triggered flip-flop circuit? (2 marks)

14. Using the laws of Boolean algebra, simplify the following Boolean expression (1 mark)
`A.B. (A + B)`

15. Using the laws of Boolean algebra, simplify the following Boolean expression (1 mark)
`X + Y).(X + NOT Y)`