Electric current and its effects.pptx

Grade 7

1. E lectric current and its effects

2. ELECTRIC CIRCUIT Electric circuit is the path in which electric current flows from a source across various components. Electric circuit diagram is the diagrammatic representation of an electric circuit.

3. ELECTRIC COMPONENTS The various parts/elements that are used to make an electric circuit are called electric components. EXAMPLE– cell, battery, connecting wires, bulb, switch, etc. Battery is a combination of two or more cells.

4. SWITCH BATTERY & CELL BULB WIRES

5. Phet Simulation- Electric circuit construction https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

6. What makes electric iron hot?

7. HEATING EFFECTS OF ELECTRIC CURRENT Water heaters (geysers), electric irons, room heaters, etc. are some electric devices in which heat is produced. Electricity produces heat, i.e. part of the electric energy is converted into heat energy. This is called heating effects of electric current.

8. ELECTRIC APPLIANCES

9. HEATING ELEMENTS All appliances which produce heat on passing electricity are based on the principle that heat is produced when electricity is passed through a wire. This wire or coil of wire is known as element/heating element. The amount of produced in a wire depends on the length,thickness and the material of the wire.

10. Good conductors are those which allow electricity to pass through them. The amount of heat produced depends on how good or poor a conductor the material of wire is. More heat is produced if the material of wire is not a conductor. Hence ,heating elements are made up of materials which have low conductivity or high resistance.

11. Resistance is defined as the opposition to the flow of electrical current through a conductor. It's important to point out that conductivity and resistivity (the property that determines final resistance) are inversely proportional. https://youtu.be/LWwBSGCiRGM

12. Common materials used for heating element are tungsten and nichrome. Nichrome is a material made up of nickel , iron and chromium(alloy). The filament of an incandescent bulb is made up of tungsten.

13. IRON NICKEL TUNGSTEN NICHROME

14. HOUSEHOLD SAFETY DEVICES There are two types of household devices: Fuse MCB(miniature circuit breaker)

15. Tungsten (W) 3380°C Rhenium (Re) 3180°C Osmium (Os) 3027°C Tantalum (Ta) 3014°C Molybdenum (Mo) 2617°C Niobium (Nb) 2468°C Iridium (Ir) 2447°C Ruthenium (Ru) 2250°C Mercury (Hg) -39 Francium** (Fr) 27 Cesium (Cs) 28 Gallium (Ga) 30 Rubidium (Rb) 40 Potassium (K) 63 Sodium (Na) 98 Indium (In) 157 Lithium (Li) 180 Tin (Sn) 232 Polonium** (Po) 254 Bismuth (Bi) 271 Thallium (Tl) 304 Cadmium (Cd) 321 Lead (Pb) 327

16. FUSE MCB

17. FUSE- a fuse is a household safety device which is based on the principle of heating effects of electricity. A fuse consists of a wire that breaks when high electricity is passed through it. This can break can the circuit and prevent the current from entering devices and causing damage to the devices and possible fire. MCB- MCBs are also safety devices used in households. Like fuses ,MCBs too break the circuit or go off automatically by overload in the circuit .

18. FUSES An electric fuse is a device that is used to prevent the damage that can be caused by an excess of electric current. According to the heating effect of the electric current, a wire becomes hot as current is passed through it. However, if an excess of current is passed through a wire it can melt or break. The electric fuse consists of a wire which is made up of a metal or an alloy which has a low melting point. As a result, the wire breaks down easily as high current passes through it. As the wire breaks the circuit of the fuse opens and hence no for the current passes through it. This can prevent a short circuit for fire due to high electric current. Different types of fuses are used for different devices and some are also available for houses as we.

19. Fuse https://www.youtube.com/watch?v=BLIYsRwKrkE

20. H OW CAN EXCESSIVE CURRENT PASS THROUGH A CIRCUIT ? Reasons why excessive current can pass through a circuit: Sometimes we connect different devices to the same socket which results in drawing of more current from that socket. As a result, the load on the circuit increases and it can lead to a short circuit or fire. When the insulation of wires gets torn away, the wires can come in contact with each other which cause a spark or may lead to a fire (short circuit). This is why fuses are used to prevent any kind of short circuit and overloading.

21. https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

22. MINIATURE CIRCUIT BREAKER OR MCB A miniature circuit breaker or MCB is generally used instead of fuses. A fuse breaks due to excessive current so that the circuit opens up and the damage can be prevented. However, once a fuse breaks down it cannot be used again. MCB, on the other hand, is a switch which turns OFF on its own when a circuit overloads. Once the problem the circuit is rectified we can switch ON the MCB once again.

23. M AGNETIC EFFECT OF ELECTRIC CURRENT When an electric current is passed through a wire it behaves like a magnet. This is called the magnetic effect of the electric current which was discovered by a scientist, Hans Christian Oersted. He discovered that the needle of a compass deflects when an electric current is passed through a wire placed near the compass. This indicates that a magnetic field is created near the wire that deflects the needle.

24. MAGNETIC EFFECTS OF ELECTRICITY A conducting wire behaves like a magnet when electricity is passed through it and hence the needle in the magnetic compass gets deflected. Factors on which magnetic effect of electric current depends- It is directly proportional to the number of turns in the coil It is directly proportional to the amount of current.

25. ELECTROMAGNET Electromagnet is a temporary magnet in which a current carrying wire behaves like a magnet.

26. USES- They are used in devices and appliances like motors,generators ,and loudspeakers ,hard disks , MRI machines,etc. 2. They are used in magnetic levitation by which an object is suspended with no support other than magnetic fields. 3. They are used for separating iron materials from junk. They are used in separation of iron from ore. They are used to magnetise and make permanent magnets.

27. ELECTRIC BELL An electric bell is based on the principle of electromagnetism.

28. CONSTRUCTION- An electric bell consists of a curved iron rod mounted on a metallic strip ,a switch , a hammer , a gong and a source of electricity. The connecting wire is wounded over the iron rod so that it behaves like an electromagnet when current passes through it. One end of the wire is connected to a contact screw through a switch and a source of electricity. The end of the wire is connected to the lower end of the hammer, which is called armature. This armature rests on the contact screw and a metallic gong is placed in front of the hammer.

29. WORKING- When the switch is pressed on ,the current flows through the wire and the iron rod becomes an electromagnet. The electromagnet attracts the armature , and as the armature moves towards the gong, it strikes the gong to produce sound. Meanwhile, the connection between the armature and the contact screw breaks ,resulting in a break in the circuit. Because of this ,the iron rod ceases to be an electromagnet and the armature returns to the original position. This process is repeated till the time he switch is kept in the on position.

30. Simulation https://interactives.ck12.org/simulations/physics/doorbell/app/index.html