Physics - Senior Secondary 2 - Electric Fields

Electric Fields

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TERM: 2ND TERM

WEEK: 10

Class: Senior Secondary School 2
Age: 16 years
Duration: 40 minutes for each of 5 periods
Date:
Subject: Physics
Topic: Electric Field
Subtopics:
• Shunts and multipliers (Galvanometer conversions)
• Principle of the potentiometer
• Wheatstone bridge
• Meter bridge

SPECIFIC OBJECTIVES:
By the end of the lesson, students should be able to:

  1. Explain the principle and applications of shunts and multipliers in galvanometer conversions.
  2. Understand the working principle of the potentiometer and how it is used to measure voltage.
  3. Set up and calibrate a potentiometer circuit.
  4. Understand the working principle of the Wheatstone bridge and its use in determining unknown resistance.
  5. Set up and use a meter bridge to measure resistance.

INSTRUCTIONAL TECHNIQUES:
• Explanation
• Demonstration
• Hands-on activity
• Questions and answers
• Practical setup of circuits and experiments
• Video clips on shunts, potentiometer, Wheatstone bridge, and meter bridge

INSTRUCTIONAL MATERIALS:
• Galvanometer
• Shunts and multipliers
• Potentiometer
• Wheatstone bridge setup
• Meter bridge setup
• Resistors (known and unknown)
• Power supply
• Physics textbook
• Whiteboard markers
• Videos on galvanometer conversions, Wheatstone bridge, and meter bridge

INSTRUCTIONAL PROCEDURES

PERIOD 1-5
PRESENTATION

STEP 1: INTRODUCTION
• Begin by asking students if they have heard about galvanometers, potentiometers, or Wheatstone bridges before.
• Discuss the importance of these instruments in measuring small voltages, resistances, and calibrating circuits.
• Introduce the topic of electric fields and mention how these devices are used in practical applications.

 

STEP 2: EXPLANATION (Shunts and Multipliers)
• Define a galvanometer and its limitations.
• Introduce shunts and multipliers as devices used to extend the range of a galvanometer.
• Explain the principle of shunts (connected in parallel to decrease current) and multipliers (connected in series to increase voltage).
• Show how the formula for current measurement changes when using a shunt.
• Provide practical examples of how these devices are used in electrical measurements.

 

STEP 3: DEMONSTRATION (Potentiometer)
• Explain the principle of the potentiometer as a device used to measure potential difference (voltage) without drawing current from the circuit.
• Show how to set up a potentiometer circuit, ensuring that students understand the role of the sliding contact and the standard cell used to measure voltage.
• Demonstrate how to calibrate a potentiometer by adjusting the sliding contact until the galvanometer shows zero current, indicating a balance.

 

STEP 4: DEMONSTRATION (Wheatstone Bridge)
• Explain the principle of the Wheatstone bridge as a method for accurately measuring unknown resistance.
• Discuss the four resistances in the Wheatstone bridge circuit: two known resistors, one unknown resistor, and a variable resistor.
• Show how to balance the bridge using the galvanometer and explain how resistance is calculated from the bridge's balanced condition.

 

STEP 5: HANDS-ON ACTIVITY (Meter Bridge)
• Introduce the meter bridge as a practical instrument to measure resistance using the principle of the Wheatstone bridge.
• Guide students to set up the meter bridge circuit, ensuring the correct placement of known and unknown resistors, and the use of a jockey to make contact on the bridge wire.
• Allow students to measure the unknown resistance by balancing the bridge, and calculate resistance based on the measured lengths.

 

STEP 6: NOTE TAKING
• The teacher writes a summary note on the board, which students will copy.

 

NOTE:

Shunts and Multipliers:
• Shunt: A low-value resistor connected in parallel to the galvanometer to divert most of the current, allowing for larger current measurement.
• Multiplier: A high-value resistor connected in series to the galvanometer to measure higher voltages.

Potentiometer Principle:
• A potentiometer measures potential difference by comparing it with a known voltage, ensuring no current is drawn from the circuit.
• Calibration: Adjust the sliding contact until the galvanometer reads zero, indicating a balance.

Wheatstone Bridge:
• Used to measure unknown resistances by balancing a bridge circuit with known resistances.
• The resistance is calculated using the ratio of known resistances.

Meter Bridge:
• A practical device based on the Wheatstone bridge used for measuring resistance.
• The resistance is determined by balancing the bridge with the jockey and measuring the lengths of the bridge wire.

 

EVALUATION

  1. What is the purpose of using shunts and multipliers with a galvanometer?
  2. Describe the principle of a potentiometer and how it is calibrated.
  3. What is the Wheatstone bridge used for, and how do you calculate unknown resistance?
  4. How do you measure unknown resistance using a meter bridge?

CLASSWORK:
• Draw the circuit diagram for a Wheatstone bridge and label the components.
• Calculate the unknown resistance from a balanced Wheatstone bridge circuit given the known resistances and the length of the bridge wire.

 

CONCLUSION:
• The teacher will review the students' answers and provide positive feedback.
• Encourage students to reflect on the importance of accurate resistance and voltage measurement in practical electrical systems.
• Inform students about how these concepts are used in real-world applications like electronics, power distribution, and circuit design.