Basic Electricity - Senior Secondary 2 - Conversion of millimeter into ammeter, voltmeter and ohmmeter

TERM: 2^ND TERM

WEEK SIX

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC ELECTRICITY

Topic: CONVERSION OF MILLIMETER INTO AMMETER, VOLTMETER AND OHMMETER

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Convert a millimeter (mm) into a high range ammeter, voltmeter, and ohmmeter

II.) Vary the range of a meter with multipliers

III.) Vary the range of a meter with stunts

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

CONVERSION OF MILLIMETER INTO AMMETER, VOLTMETER AND OHMMETER

Converting a millimeter (mm) into a high range ammeter, voltmeter, and ohmmeter would require significant modifications and additional components. Below is a general approach for each:

1. High-Range Ammeter: For a high-range ammeter, you would need to incorporate a shunt resistor into the circuit. The shunt resistor would bypass most of the current around the meter movement, allowing only a small fraction to pass through the meter. By carefully selecting the resistance value of the shunt, you can scale the current to be within the range of the meter movement.
2. High-Range Voltmeter: To convert a millimeter into a high-range voltmeter, you would need to use a voltage divider circuit. This circuit consists of resistors that divide the voltage being measured into a smaller fraction that can be safely measured by the meter movement. By selecting appropriate resistor values, you can scale the voltage down to within the range of the meter movement.
3. High-Range Ohmmeter: Converting a millimeter into a high-range ohmmeter involves incorporating a constant current source and a voltage measurement circuit. The constant current source would pass a known current through the resistance being measured, and the voltage drop across the resistance would be measured. Using Ohm's law (V = IR), the resistance can be calculated based on the measured voltage and the known current.

Varying range of Meters

1. Multiplier for Varying Meter Range:

To vary the range of a meter, like an ammeter or voltmeter, you can connect a resistor in series with the instrument. This resistor, often referred to as a multiplier resistor, scales the range of the meter by adjusting the voltage or current applied to it. By selecting the appropriate resistance value, you can expand or contract the range of the meter to suit different measurement requirements. For example, in a voltmeter, a multiplier resistor can be connected in series to extend the range of voltage measurements.

2. Shunt for Varying Ammeter Range:

To vary the range of an ammeter, you can connect a shunt resistor across the instrument. A shunt resistor provides an alternate path for current to bypass the meter movement, effectively dividing the current between the meter and the shunt. By carefully selecting the resistance value of the shunt, you can adjust the range of the ammeter to measure higher currents while ensuring that only a small fraction of the total current passes through the meter movement. This technique allows for the measurement of currents beyond the original range of the ammeter.

EVALUATION: 1. Explain how to convert a millimeter (mm) into a high range ammeter

2. Discuss briefly how to vary ammeter range with a stunt

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively