Electronics 3

Act 3

• Multimeter
• Series parallel circuits
• Circuit symbols
• Switches / Resistors

Measuring Tools

Questions

1. What is a multimeter?
2. How is a multimeter used to measure voltage, current?

A multimeter is a simple tool used to measure Voltage, current or Resistance. Watch the video here.

• Voltage : Tap the probe in parallel with the components you want to measure.
• Current: Connect the probe in series with the components you are measuring.
• When measuring voltage and current, multimeters are connected/ tap together with the circuits with batteries and other components.
• Multimeters can also be used to measure resistance and check if a circuit is working. ( testing for open or closed circuit)

Series and Parallel circuit. Watch the video here

Questions

1. Draw and explain a simple series and parallel circuits using two bulb, a cell and switches.
2. What are the difference between series and parallel circuits?
   • In terms of the voltage across the bulb?
   • In terms of the current flowing across the bulb?

Circuit Symbols

Circuit symbols are used in circuit diagrams showing how a circuit is connected together. To build a circuit you need a different diagrams to show how the components are connected together.

The List of common circuit symbols are shown here. Not all are part of D&T syllabus.

Questions

Draw and label the circuit symbol of the following

1. Cell
2. Resistor
3. LED
4. Capacitor
5. LDR: Light dependent resistor
6. diode
7. NPN Transistor
8. Bulb/Lamp (indicator)
9. Motor
10. Buzzer
11. Switches : SPDT/ SPST / DPDT /DPST / Push to break switch/ Push to make switch
12. Variable resistor
13. Potetiometer

Switches

1. What are the different types of switches available.
2. How to apply switches in Series and parallel circuit.

Common types of switches used in Electronics circuits are

• SPST: Single pole Single Throw
• SPDT: Single Pole double Throw
• DPST: Double throw Single Throw
• DPDT: Double pole double throw

Watch the first 4 minute of the video here.

Resistors

• A Resistor is an electronic component used to control the current flowing in a circuit.
• We learned that ohms law state that V = IR. Therefore to control the flow of current in a circuit, we can either control V or R.
• We control V by varying the voltage ( adding more batteries in series)
• We control Current (I) by adding or reducing resistance. Increasing resistance by means of adding resistor in a circuit.

Types of Resistor and how to obtain their values.

• There are two main types of resistors.
• Fixed and variable resistors.
• Fixed resistors have values that cannot be changed.
• Variable resistors are types which values are adjustable.
• Example of Variable resistors are potentiometer.

Understanding Resistor values

• There are 2 ways to obtain the values of a fixed resistor.
  • Measure with a multimeter
  • Read the value from the color code on a resistor
  • Watch this video on how to read the color code of resistor.
  • You are not required to memorise the color code but you need to know how to read the resistor value given the color code and table)
  • 1st band represent the first digit
  • 2nd band represent second digit
  • 3rd band represent the multiplication factor
  • last band ( gold / silver) represent the tolerance level 5% or 10%

Questions:

• Whats is the value of a resistor if the color code is Brown , Black, red, gold?

Potentiometer

• A potentiometer is a variable resistor . It has a turning knob and 3 terminals
• The turning know allows you to adjust the value of the resistor.
• What happens when you turn the knob of a potentiometer. What the video here.
• Connecting between terminal 1 and 3 gives the maximum resistance. Connecting between 1 to 2 or 2 to 3 provides variable resistance.