Electricity_Part 1_for grade middle school.pptx

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1. Electricity understand how electricity flows around a circuit • learn about the electrons that flow to make electric current.

2. Look at the circuit in the picture. When you close the switch, the lamp lights up. What is moving in the circuit?

3. The cell in the circuit has two connections, called terminals. The terminals are labelled with + and − symbols, meaning positive (+) and negative (−). When connected into a circuit, the negative terminal of a cell, battery or power supply pushes electrons around in the wires. All materials contain atoms. Atoms contain smaller particles. An electron is one type of smaller particle in an atom. The flow of electrons in the circuit is called current.

4. Metals consist of giant structures of atoms arranged in a regular pattern. The electrons from the outer shells of the metal atoms are delocalised , and are free to move through the whole structure. A model showing how metallic bonds are formed - the first diagram shows the outer electrons in their atoms, and the second diagram shows that the electrons have become delocalized. https://www.youtube.com/watch?v=7RpyURBNZyU

5. What does the phrase "sea of electrons" describe? The electron sea model pictures the electrons on the surface of a metal being free to move from one atom to another. 

6. Therefore, electrons will be attracted towards the positive terminal of the power supply and be repelled from the negative terminal. If there is a break in the circuit, all the electrons stop flowing. Electrons can only flow in a complete circuit. https://www.youtube.com/watch?v=nzmoGca5rXc

7. Electrical circuits learn how to draw and compare circuit diagrams learn the circuit symbols for cells, switches, lamps, buzzers and ammeters Discuss with your partner the role of each of these components in a circuit: a cell b switch c lamp d buzzer e ammeter.

8. Circuit diagrams

9. Circuit diagrams Advantages of circuit diagrams compared with pictures • Circuit diagrams are easier to draw. • The components have standard symbols which are used across internally. • Wires are drawn with straight lines, which is easy to interpret.

10. Circuit symbols What is an ammeter? Ammeter is an electrical measuring device to measure electric current through the circuit. The normal symbol of ammeter is capital A mentioned inside a circle.

11. Circuit symbols A cell provides energy for the current to flow in a circuit. A battery has multiple cells put together that provides more energy for the current to flow in a circuit.

12. Circuit symbols A lamp gives out light An open switch - stops the flow of current when opened

13. Circuit symbols A buzzer makes a buzzing sound A closed switch - starts the flow of current when closed

14. Circuits Take care when drawing circuit diagrams. Make sure: • there are no gaps in the lines, especially at the corners and where wires meet components • wires are not drawn through components.

15. Circuits

16. Circuit diagram This circuit contains a cell, a switch and a buzzer. The circuit could be used in a doorbell. If the switch is pushed outside a door, it makes the buzzer sound and attracts attention inside

17. Circuit diagram This circuit contains a cell, a switch, a lamp and an ammeter. The ammeter measures the electric current. This circuit could be used to light a room and measure the current flowing though the circuit . By measuring the current, you could tell if the cell needs to be replaced – a smaller current means the cell is low on stored energy. The lamp would also become less bright, but you might not notice until too late and you find yourself sitting in the dark!

18. Measuring the flow of current learn the unit for measuring current learn how to measure current learn a rule about current in series circuits

19. Measuring the flow of current An ammeter is an instrument used for measuring electric current in units of amperes. An ammeter must be connected in series with the path of the current being measured . Analog ammeter Current is measured in units called amperes. It is denoted by the symbol A

20. When electrons move more quickly, the current increases. When electrons move more slowly, the current decreases. Look carefully at the ammeters in the picture. They both have two terminals, for wires to be attached. One terminal is red and the other terminal is black. In a circuit, the red terminal of the ammeter must be connected to the positive terminal of the power supply. The red terminal may be connected directly, or through other components, to the positive terminal of the power supply Both ends of the ammeter are the same in a circuit diagram. You do not need to show the red and black terminals on the circuit symbol for an ammeter.

21. To  measure the current of a circuit , the ammeter is connected in series in the circuit so that the current to be measured must pass through it. Since, the resistance of ammeter is low , so its inclusion in series in the circuit does not change the resistance and hence the main current in the circuit.

22. In a series circuit, if more ammeters are connected at different points, they will all show the same current.

23. Conductors and insulators discover the difference between electrical conductors and insulators • learn about uses for conductors and insulators • test some materials for electrical conduction or insulation

24. Conductors and insulators

25. Conductors and insulators When current flows, electrons move. Therefore, a conductor is a material in which electrons are free to move. Conductors allow electrons to flow. Wires that carry electric current are made from metal. Most wires in houses and schools are made from copper, with a plastic coating. Wires that cover long distances are usually made from aluminium or steel. These metals are cheaper than copper.

26. Conductors and insulators

27. Conductors and insulators Some circuits, such as those in phones and laptops, do not use wires. The printed circuit board in the bottom right picture has copper tracks instead of wires. The tracks are green because the copper is coated with another Material .

28. Conductors and insulators What is an insulator? An insulator is a material that does not conduct electrical current. Insulating materials include paper, plastic, rubber, glass and air. Vacuum is also an insulator, but is not actually a material.

29. Conductors and insulators What is an insulator? An insulator is a material that does not conduct electrical current. Insulating materials include paper, plastic, rubber, glass and air. Vacuum is also an insulator, but is not actually a material. In an insulator, the electrons are not free to move. Because the electrons are not free to move, current cannot flow. Insulators inhibit electron flow

30. Conductors and insulators Most electrical conductors are covered by insulation. Insulators are used to keep people safe from electricity. Plastic insulation on wires is also useful because the plastic can be coloured differently to identify each wire.

31. Conductors and insulators The insulators on these power lines stop the current from flowing from the wires into the metal pylon. If the current flowed to the pylon, electrical energy would be dissipated into the ground. Also, people and animals touching the pylon would get electric shocks D ampers additionally dampen any vibration in the lines  spacers are used to  ensure sufficient distance between conductors   Metal pylon