This section contains carefully selected MCQs and Previous Year Questions with explanations to help students understand concepts and prepare effectively for examinations, interviews, and competitive tests.
Q: 1The characteristic equation of the T flip-flop is
Option B
The characteristic equation of a flip-flop defines the next state Q(n+1) in terms of the present state Q(n) and the input. In the case of a T flip-flop, when T = 0, the output remains unchanged, meaning the next state is the same as the present state. When T = 1, the flip-flop toggles, so the next state becomes the complement of the present state.
This behavior can be expressed mathematically as: Q(n+1) = T ⊕ Q(n) which is equivalent to Q(n+1) = T·Q̅(n) + T̅·Q(n).
Q: 2In a positive edge triggered JK flip-flop, when J=0, K=1 and Q=0, what happens to Q when the clock input goes HIGH and when the clock input goes LOW?
Option A
A positive edge triggered JK flip-flop changes its output only at the rising edge of the clock.
A rising edge (positive edge) is the moment when a digital signal changes from LOW (0) to HIGH (1).
In digital electronics, clock signals are square waves that continuously switch between 0 and 1. The transition from:
0 to 1 (LOW to HIGH) is called the Rising Edge.
1 to 0 (HIGH to LOW) is called the Falling Edge.
First, recall the JK flip-flop truth table:
| J | K | QN+1 | Operation |
|---|---|---|---|
| 0 | 0 | QN | No Change |
| 0 | 1 | 0 | Reset |
| 1 | 0 | 1 | Set |
| 1 | 1 | Q’N | Toggle |
When clock goes HIGH:
Since it is positive edge triggered, the flip-flop responds only at the rising edge. At this moment, reset condition applies, so, Q becomes 0. But Q was already 0. So, it remains 0.
When clock goes LOW:
After the rising edge, the flip-flop does not respond to further clock level changes. So, Q remains unchanged (still 0).
Q: 3In the given sequential circuit if the initial value of Q1Q0 = 00, then what are the next three values of Q1Q0?
Option B
The given circuit contains two T Flip-Flops. A T Flip-Flop changes (toggles) its output whenever value of T is 1and a clock pulse is applied.
In the circuit:
Initial state is given as: Q1Q0 = 00
| Clock Pulse | Q0 Change | Q1 Change | New State (Q1Q0) |
|---|---|---|---|
| Initial | — | — | 00 |
| 1st Pulse | Q₀ Toggle from 0 to 1 | Q₁ Toggles from 0 to 1 | 11 |
| 2nd Pulse | Q₀ Toggle from 1 to 0 | No Toggle (No Change) | 10 |
| 3rd Pulse | Q₀ Toggle from 0 to 1 | Q₁ Toggles from 1 to 0 | 01 |
Thus, the next three states (Q1Q0) are 11, 10, 01.
Q: 4Which of the following options is not true for a gated D-type flip-flop?
Option D
A gated D-type flip-flop is a sequential circuit that stores one bit of data. The transfer of input D to output Q is controlled by a clock signal.
When the clock is high (1), the flip-flop becomes active and the input data D is transferred to the output Q.
When the clock is low (0), the flip-flop does not allow the input to pass through and the previous value stored in Q is maintained.
Q: 5When does a negative level triggered flip-flop in Digital Electronics changes its state?
Option A
A negative level triggered flip-flop is a type of flip-flop that changes its state only when the clock signal is at the low level (0). In other words, when the clock remains at a negative (low) voltage level, the flip-flop becomes active and responds to inputs.
Q: 6Which of following circuit is used as a memory device in computer?
Option A
A memory device is used to store information so that it can be used later. A Flip-Flop is a binary cell that capable of storing one bit of information. The flip-flop has two stable states either 0 called RESET or 1 called SET.
Q: 7What is the correct answer of the given statements in the given order?
I. Gate in which output of logical gate is high when all inputs are high is ________
II. Half of byte is known as ________
III. A flip-flop whose output follows the input when triggered is ________
Option C
A logic gate whose output becomes high (1) only when all inputs are high is called an AND Gate.
| A | B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
A byte contains 8 bits. Half of a byte means 4 bits. A group of 4 bits is called a Nibble.
A D Flip-Flop is a flip-flop whose output follows the input when the clock signal is triggered.
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