An in dept, thorough, detailed, effective and efficient set of Technology study notes covering the section Electrical systems and control for grade 9 term 3 content. The notes are in the format of Summary, Self Test Questions and Answers.
Chapter 6 : Electrical systems and control
Unit 1: Revision of Electric Circuits and Components
Summary:
Cells in Series:
● - Cells in series increase the voltage in a circuit.
● - Higher voltage makes lamps shine brighter.
Cells in Parallel:
● - Cells in parallel increase energy capacity.
● - They keep the circuit running longer but don't increase voltage.
Lamps in Series:
● - Lamps connected in series are less bright than a single lamp.
Lamps in Parallel:
● - Lamps connected in parallel shine as brightly as a single lamp.
Logic Gates:
● - AND logic gates use switches connected in series.
● - OR logic gates use switches connected in parallel.
Conventional Current:
● - Electric current moves from the positive terminal to the negative terminal.
● - This flow is known as conventional current.
Ohm's Law:
● - Current is proportional to potential difference, provided resistance is constant.
● - Useful for circuit calculations.
Component Symbols:
● - Cells, lamps, and switches in series/parallel circuits.
● - Comparing brightness in different circuits.
,Self Test Questions:
1. What happens to the voltage in a circuit when cells are connected in series?
2. Explain how cells connected in parallel affect the energy capacity in a circuit.
3. Why do lamps connected in series shine less brightly?
4. How are AND logic gates constructed, and what is their purpose?
5. Describe the direction of conventional current in an electric circuit.
Answers:
1. Cells in series increase the voltage in a circuit, making lamps shine brighter.
2. Cells in parallel do not affect voltage but increase energy capacity, extending the circuit's run time.
3. Lamps connected in series are dimmer because they share the voltage.
4. AND logic gates use switches connected in series to create an output only when all inputs are ON.
They are used for specific conditional actions.
5. Conventional current flows from the positive terminal of the cell to the negative terminal in an electric
circuit.
Unit 2 Ohm's Law and resistance
Summary:
Ohm's Law:
● - Ohm's Law states that current strength in a conductor is directly proportional to the potential
difference across it if the resistance remains constant.
● - The formula for Ohm's Law is V/I = R, where V is voltage (measured in volts), I is current
strength (measured in amperes), and R is resistance (measured in ohms).
Calculating Voltage, Current, and Resistance:
● - You can use the formulas V = I x R, I = V/R, or R = V/I to calculate voltage, current, or
resistance in electric circuits.
Resistor Color Codes:
● - Resistors have a color code with bands representing their resistance value.
, ● - The accuracy rating of resistors can be 2%, 5%, or 10%, indicated by the color of the fourth
band.
Decoding Resistor Color Codes:
● - Use a decoder chart to read the color bands on a resistor.
● - For example, green (band 1) represents 5, orange (band 2) represents 3, and red (band 3)
indicates two additional zeros. So, the resistance is 5300 ohms with a 5% accuracy rating.
Self Test Questions:
1. What does Ohm's Law state, and how is it represented mathematically?
2. Explain the units used to measure voltage, current strength, and resistance.
3. What are the three rearrangements of the Ohm's Law formula?
4. How can you calculate the resistance if you know the voltage and current?
5. How is the resistor's accuracy rating indicated in its color code?
Answers:
1. Ohm's Law states that current strength is directly proportional to potential difference if resistance is
constant. It is represented as V/I = R.
2. Voltage is measured in volts (V), current strength in amperes (A), and resistance in ohms (Ω).
3. The three rearrangements of Ohm's Law are V = I x R, I = V/R, and R = V/I.
4. To calculate resistance, use R = V/I when you know voltage and current.
5. The accuracy rating of a resistor is indicated by the color of the fourth band in the color code. Red
represents 2%, gold represents 5%, and silver represents 10%.
Summary
● Electric components are represented by symbols in circuit diagrams.
● Conventional current in a circuit moves from the positive terminal of the energy source to the
negative terminal.
● Cells connected in series increase the voltage across the circuit. Cells connected in parallel do not
increase the circuit voltage.
● Lamps connected in series shine less brightly than one lamp on its own.
● Lamps connected in parallel shine as brightly as one lamp.
● Switches connected in series form an AND logic gate.
● Switches connected in parallel form an OR logic gate.
● Ohm's Law states that the current through a conductor is directly proportional to the potential
difference across the conductor provided the resistance of the conductor remains constant.
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