Technology Grade 8 Term 3 2018 Question Paper

ⓘ Below are Question 2 explained answers by CAPS AI (supervised by Natural Sciences Teachers)

2.1 Explain how you would connect switches to form an AND logic gate (4)

To form an AND logic gate, connect two switches in series.

• This means placing one switch after the other in the same line.

• The circuit will only work (turn on the output like a light bulb or LED) if both switches are closed (ON) at the same time.

• If either switch is open, no current flows, and the output stays off.

Summary: Connect both switches in a row (series) so that both must be ON for the circuit to work.

2.2 Explain how you would connect switches to form an OR logic gate (4)

To form an OR logic gate, connect two switches in parallel.

• This means placing the switches next to each other, each making a separate path to the output.

• The circuit will work (turn on the output) if either one OR both switches are closed (ON).

• Current can flow through any one closed path.

Summary: Connect the switches side by side (parallel) so the output works when at least one is ON.

2.3 Write a sentence in which you explain Ohm’s Law (4)

Ohm’s Law states that the current in a circuit is directly proportional to the voltage and inversely proportional to the resistance.
This means:

• If voltage increases, current increases.

• If resistance increases, current decreases (if voltage stays the same).

2.4 Give the formula for Ohm’s Law (4)

The formula is:

$\mathrm{<strong>V\; =\; I\; x\; R</strong>}$

Where:

𝑉 = Voltage (in volts)

𝐼 = Current (in amperes)

𝑅 = Resistance (in ohms)

Let me know if you’d like example problems using this formula.

2.5 Draw the symbol and name the unit in which the following electrical quantities are measured:

a. Potential difference

• Symbol: Single long line connected to a single short line (battery/cell symbol), or labelled as V or ΔV. Shown in image below.
  

  

   

• Unit: Volt (V)

  • One volt is defined as one joule per coulomb of charge

b. Current

• Symbol: A circle with the letter A, or just the letter I in circuit diagrams.

  • Typically labeled A (ampere) or I (current) in schematics, see it’s image below.
    

    

     

• Unit: Ampere (A)

  • Defined as the rate of flow of one coulomb of charge per second.

c. Resistance

• Symbol: Zigzag (standard resistor symbol) or a rectangle (IEC style).

  • See the zigzag lines in the image below
    .

    

• Unit: Ohm (Ω)

  • One ohm is the resistance that allows one ampere to flow under the application of one volt.

2.6
a) A length of resistance wire has a resistance of 8 Q. Calculate the current through it when a voltage of 56 V is applied across it. (4)

To calculate the current, use Ohm’s Law: V = I × R

Where: $$\begin{aligned}
& V=56\mathrm{V~(volts)} \\
& R=8\Omega \\
& I=?\text{ (current in amperes)}
\end{aligned}$$

Rearranged formula:

$$I=\frac{V}{R}=\frac{56}{8}=7\mathbf{A}$$

Final Answer: The current is 7 amperes (A).

b) What electronic component is shown in the diagram below

On the right side of the image, this shows the circuit symbol for a transistor.

Specifically, this appears to be an NPN transistor (or bipolar junction transistor), as indicated by:

• The three terminals (base, collector, and emitter)
• The arrow on the emitter pointing away from the base
• The “base” label shown in the diagram

The three lines represent the collector, base, and emitter terminals of the transistor.

c) Copy the symbol and write in the two missing labels.

1. Amplification – A transistor can amplify electrical signals, taking a small input signal and producing a larger output signal with the same characteristics.
2. Switching – A transistor can act as an electronic switch, turning electrical current on or off by controlling the flow of current between its collector and emitter terminals based on the signal applied to the base.

2.7

a. Conducts electrical current in one direction only and lights up when it does so

Answer: Light Emitting Diode (LED)

• An LED allows current to flow in one direction only and emits light when it does.

b. Changes resistance when the light intensity on it changes

Answer: Light Dependent Resistor (LDR)

• An LDR (also called a photoresistor) lowers resistance in bright light and increases resistance in darkness.

c. Amplifies electrical current

Answer: Transistor

• A transistor is used to amplify or switch electrical current in circuits.

2.8
a) What is a diode?

Answer (3 marks):
A diode is an electronic component that allows electric current to flow in only one direction.
It has two terminals:

• Anode (positive)

• Cathode (negative)

It blocks current in the reverse direction, protecting circuits.

b) Explain how to connect a diode correctly in a circuit.

Answer (3 marks):
To connect a diode correctly:

• Connect the anode to the positive terminal of the power supply.

• Connect the cathode to the negative terminal.

• This ensures that current flows in the forward direction and the diode works as intended.

c) What is an LED?

Answer (3 marks):
An LED (Light Emitting Diode) is a special type of diode that gives off light when current flows through it in the forward direction.
It works like a normal diode but also converts electrical energy into light energy.

d) Explain how to connect an LED correctly in a circuit.

Answer (3 marks):
To connect an LED properly:

• Connect the long leg (anode) to the positive side of the battery or power source.

• Connect the short leg (cathode) to the negative side.

• Also include a resistor in series to prevent too much current from damaging the LED.