Electricity

Samacheer, Science-Physics, Class – VII, Term – II                        V. Jayasundhar,M. Gnanamani

What makes a bulb glow!

Learning Objectives

Learners will be able to
• Know different types of cells and its uses.
• Construct simple circuits using the symbols to represent the components of the circuit.
• Analyze and solve problems in a simple circuit.
• Understand that some materials allow current to pass through and some don’t.

Pre-requisite Knowledge

• Knowledge of different types of energy and that Electricity is one of them.
• Awareness of different sources of electricity like thermal, solar, hydel, wind, fossil fuels, etc.
• General awareness about how electrical equipment work viz. electricity flows through the wires, using a device for a long time can generate heat and harm the appliances, the role of a switch etc.
• Purpose of using batteries in toys, remote controls, clocks etc.
• Basic understanding of the conversion of energy into multiple forms and the law of conservation of energy.

ENGAGE

The teacher elicits the prior knowledge of the students using a KWL Chart. 

Group Activity:

Children are asked to share their ideas on electricity within their group and write on the KWL Chart. The teacher can give an example for each of the column. Students are instructed to fillonly the first two columns and the third column will be filled once they learn the entire lesson.

Once they have made their KWL charts, each team shall be given few (2-3) minutes to share their ideas and doubts on electricity to the entire class. The learners can keep adding on questions and doubts in the “Want to know” column throughout the lesson.

EXPLORE

1.1 Generation of electricity:
Setting: Whole class The teacher engages the class with a discussion on electricity that triggers excitement among students. The teacher then asks if electricity can be produced in the class and what are the things that might be required to generate electricity?
DEMO: The teacher makes a light glow in front of the class using a dynamo and asks the children what makes the light glow? How does this device generate electricity? The teacher can open a toy motor to show its components and allow children to explore it. Students can explore components like the coilaround the armature, the magnets, the brush etc. They are asked to write any questions/ doubtsthat arise in the Want to know column of KWL chart.
The teacher shares the difference betweena dynamo and motor and discusses other ways of generating electricity like hydel, thermal, atomic, wind, solar etc. with examples closest to Puducherry.
Question: How else can we generate electric current?
Individual / Pair activity:
Students are asked to make an LED bulb glow using lemons and potatoes. A normal dry cell can also be used. The teacher explains that electricity is produced in the electric cells by reaction of the chemicals inside the cell. Here, chemical energy is converted into electrical energy. Here, they discuss the law of conservation of energy and the teacher establishes that energy from water, heat, wind, sun, chemicals can also be transformed into electrical energy.
1.2 Electric cells:
Types of electric cells:
Setting: Individual/ Pair activity The teacher distributes electric cells (both primary and secondary electric cells) of different volts [1.5V (AA, AAA), 3.7V, 9V etc.], shapes and sizes, etc. and asks the students to predict which
of these cells can generate maximum electrical energy?
The teacher takes the opinion of the class and asks the groups to come up with a way to test their prediction.
Materials required:
Motor, blade of a fan, different batteries, wires etc. The learners are made to try different batteries with the same motor and blade. They observe and record the difference in the speed of rotation of the blades of the fan. The higher the electrical energy from the cell, the faster the rotation of the blades.

Question: Can the power of an electric cell be identified by looking at the cell?
Look for “V”- 1.5V, 9V, 3.7V; AA, AAA, etc. on the cells and ask them to observe and record their observations.

The teacher elicits the similarities and differences in the sizes, shapes and other observable features found on the cells given to them and discusses their uses.
The teacher poses questions for students to understand the difference between primary and secondary electric cells.
Q. What happens to the cells in torches, remote controls, toys after prolonged use?
Primary electric cells: The cells which cannot be recharged and re-used are called primary electric cells. They are thrown away once the charge is drained.
Q. Do we throw the cell in a mobile phone once the charge drains off? What do we do?

Secondary electric cells: The electric cells can be recharged and reused several times are secondary cells. It will be written on the cell as “Rechargeable”.

1.3 Construction of circuits:
Setting: Pair/ Group
Safety Precautions:
Children are given clear instructions that:
1. All electrical experiments are supposed to be done only with cells only and not with any plugs at home. It can be extremely dangerous.
2. Cells should not be connected to the bulb or any other device when not required. Different materials like bulbs (working and fused), wires (conductors and insulators) and batteries (charged and dead) are given to children and they are asked to make the bulb glow. The groups are asked to explain the processadopted to make the bulb glow and the changesthey underwent during the process with reasons.

The group which still struggles to make the bulb glow can observe other groups or even take support from their peers.

EXTENSION

For students who finish earlier, they are asked to explore different ways to make a simple circuit to make a bulb glow using a cell and a switch.
1.4 Symbols for some electric circuit components:
Students are asked to draw the either theflow of current from the cell to the bulb in the circuit that they have constructed or the wiring connection to a fan or light in their house. They can either write the names or draw the pictures
to represent the fan, light, switch, wire etc.
After the students have finished with this activity, they are asked if the same drawing be done in an easier method. Here, the teacher discusses use of symbols and introduces the symbols of r components of a circuit.

Children are made to draw the simple circuits on the class board and notebook using the symbols.

1.5 Analyzing circuits:
1. What will happen in the following simple circuits? Will the bulb glow or not? Why? What can be done to make the bulb glow?

2. The + ve & - ve terminals of a cell being connected with a wire. What will happen? What should we do?

1.6 Conductors & insulators:
A set of materials (both conductors and insulators) are given to the children and they are asked to check whether they allow current to pass through.

ELABORATE

The children can be asked to make a simple model of a house with a bulb inside and outside the house. They can also design a poster to warn young children about the dangers of electricity.

EVALUATE

1. What will happen if a 9V cell is connected to small torch bulb of 2.5V and 5V? Which bulb will glow for a longer period of time? Why?

2. If we connect a small LED to a 9V cell, what will happen? Why?

3. There are a number of 1.5 volt cells. How can you make a 6 volt bulb glow? Draw the diagram of the circuit.

4. A 5V bulb connected by wires in an electric circuit with a 9V battery and a switch is not glowing. In order to make the bulb glow, what will you change?

5. List the things which you know will affect the performance of a light bulb in a circuit.

6. Why do you think we use batteries to power our circuits in school?

7. Varun built a circuit but he wants his bulb to be brighter. What could he do?

8. Draw a complete circuit (one that would work) e. her Label it
9. Draw an incomplete circuit. Explain why it wouldn’t ork?w
Teacher's Reflection
The children were excited and enjoyed working in the groups. KWL chart helped the children recollect their existing knowledge and also express their interests and doubts. This helped me understand vel their level and build upon it .

Real life examples and hands - on - activities helped the children understand the topic better. Children learn a lot on their own while engaging in hands-on activities. Relevant videos could be used to explain abstract concepts like flow of current in a conductor, induction principle,working of a bulb, etc. Children enjoyed making predictions and then testing them, drawing the symbols and circuits and presenting their ideas in front of the class. 

The terminologies and other difficult words like Turbine, Generator, Battery, Primary cell, Secondary cell, Volt, Watt, switch, LED, CFL, Incandescent light bulb, conductor, insulator etc. are to be displayed in the class throughout the lesson. We need to ensure that children do not associate the color of the wire to +ve and – ve terminals. Any wire that is connected to the +ve terminal should be considered positive irrespective of their color.

Project: A project on green energy can be experimented as a part of this lesson where students are encouraged to generate electricity from waste materials.