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4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Question 4
4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference b... show full transcript
Worked Solution & Example Answer:4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Step 1
Explain the term polarisation as used in the operation of a liquid crystal display (LCD.)
Answer
Polarisation in an LCD is the process where light waves are filtered through a polarising filter, aligning their vibrations in a single direction. An LCD uses two layers of polarised glass, and by manipulating the alignment of liquid crystals between these layers, it controls the amount of light that can pass through, thus forming images or characters on the display.
Step 2
Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode.
Answer
In a common anode seven-segment display, all the anodes (positive connections) of the LEDs are tied together and connected to a positive voltage. Each segment is activated by grounding its cathode (negative connection). In contrast, a common cathode display has all the cathodes connected together to ground, and each segment is turned on by supplying a positive voltage to its anode.
Step 3
Refer to FIGURE 4.3 below and determine the binary code at the output when the following input switches are pressed.
Answer
4.3.1 When Switch 1 is pressed, the output will be A0 = 1, A1 = 0, A2 = 0, A3 = 0, which represents the binary code 0001.
4.3.2 When Switch 5 is pressed, the output will be A0 = 0, A1 = 0, A2 = 1, A3 = 0, which represents the binary code 0010.
4.3.3 If all outputs are zero, it indicates that all input switches are turned off.
Step 4
Study FIGURE 4.4 below of the logic circuit of a full adder using two half-adders and an OR-gate. Use the table on ANSWER SHEET 4.4 to complete the truth table.
Answer
The truth table for a full adder can be completed using the following combinations:
| Ci | A | B | Sum | Co |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
Step 5
Draw the logic circuit of this flip-flop using NAND gates, NOR gates and an inverter.
Answer
The logic circuit of a D-type flip-flop can be constructed using two NAND gates and an inverter. The D input is connected to the input of the inverter, which feeds into one NAND gate along with the clock signal. The outputs of the NAND gates represent the Q and Q' (inverse output). The configuration should ensure that the flip-flop captures the D input on the clock's rising edge.
Step 6