#### Nine

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1. The flow of electrons in a definite direction is called current electricity.

i. Open electric circuit:
An electric circuit in which no current is flowing is called an open circuit.

ii. Closed electric circuit:
An electro circuit in which electric current is flowing continuously is called a closed electric circuit.

2. Any 5 points to be remembered during household wiring are:

1. Switch and fuse should be connected to a live wire.
2. The fuse should be of the proper rating.
3. Wing should be done in a dry and safe place.
4. The connection of plugs switches, etc should be strong.
5. Use of electric appliances and wires of high quality.

3. The wire which produces heat by passing a current through it is called the heating element.

4. The current which changes its magnitude and polarity is called AC.

The current that has fixed magnitude and polarity is called DC.

The frequency of current distributed in Nepal is 50 Hz means the polarity of the current changes 50 times in a second.

5. The rate at which electrical work is done or the rate at which electrical energy is consumed called electric power consumption.

1 KWhr can be defined as the amount of electrical energy consumed by an electrical appliance having a power ratio of 1KW for 1 hrs.

6. The process of producing current in a closed coil due to the relative motion between magnet and coil is called electromagnetic induction.

7. The device which converts mechanical energy into electrical energy is called a dynamo.

8. When the current is passed through a wire of high resistance which becomes extremely hot and produces light which is called the lighting effects of an electric current.

9. When the current is passed through the wire of high resistance, it becomes extremely hot and produces heat which is called the heating effect of an electric current.

10. When a current is passed through a wire, it produces a magnetic field around it which is called the magnetic effect of an electric current.

11. fig. Electric bell

12. An electromagnet is made by using a cylindrical form of an insulated copper coil having a large number of close turn is a solenoid.

It is used to strengthen the magnetic field. The device that breaks the circuit is MCB.

13. A current-carrying wire exerts a force on a magnetic compass and defects it from its usual north-south position which is called the motor effect.

When current is passed through a conductor, a magnetic field is developed around it.

14. A transformer is a device that converts high voltage AC to low voltage AC of the same frequency and vice versa The function of the step-up transformer is that it converts the low voltage of current to high voltage.

15. A transformer that converts high voltage AC to low voltage AC is called step-down transformers.
It is used at the power sub-station to decrease the AC voltage before distribution.

16. A battery charger is a device that is used to put energy into a secondary cell or rechargeable cell by forcing an electric current through it.

It is used to charge the battery of the mobile phone, automobile, laptop, etc.

17. An inverter is an electric device that changes AC into DC and vice versa. It is used to convert AC source to DC source or DC source to AC source.

18. a. Live wire and neutral wire.

 Live wire Neutral wire It carries current to the device from the source. It carries current from the device to the source. It is red or brown in color. It is black or blue in color.

b. AC and DC.

 AC DC The current that changes magnitude and polarity is called AC. The current that doesn't change magnitude and polarity is called DC. It is produced by an AC generator. It is produced by cells, batteries, etc. It has a non-zero frequency. It has a zero frequency.

c. Filament and flueoresent lamp.

 Filament Fluorescent It is filled with inert gas. It is filled with mercury vapor. Its average lifespan is about 1000 hours. Its average lifespan is about 3000 hours. It is cheaper. It is expansive. It converts 10% to light and 90% to heat energy. It converts 30% to light and 70% to heat energy.

d. Dynamo and electric motor.

 Dynamo Electric motor It converts mechanical energy to electrical. It converts electrical energy to mechanical. It works on the principle of Faraday's law of electromagnetic induction. It works on the principle of motor effects. The direction of current can be found by using fleming's right-hand rule. The direction of current can be found by using fleming's left-hand rule.

e. Step up and step down transformer.

 Step up Step down It converts low AC voltage to high AC voltage. It converts high AC voltage to low AC voltage. The number of turns is more in the secondary coil than in the primary. The number of turns is more in the primary coil than in the secondary. It is used on the power transmission line to increase voltage. It is used in household devices to run at least 220V.

f. Tungsten and nichrome.

 Tungsten Nichrome It has very high resistance. It has comparatively low resistance. It doesn't oxidize at high temperatures. It oxidizes in high temperatures. It is the wire of nickel, etc. It is the wire of copper, etc.

g. Electricity obtained from generator and battery.

 From generator From battery It generates AC electricity. It generates DC electricity. Mechanical energy is converted into electrical. Chemical energy is converted into electrical. Electricity produced by it changes its polarity. Electricity produced by it doesn't change its polarity.

19. We know, electric current flows from the phase wire to the power load. So, to block the current right at phase wire switches connected to a phase wire.

20. We know, electric current flows from phone wire to the power load. So, to disconnect or block the current right at phase wire during the case of overload, a fuse is connected to a phase wire.

21. DC is not used in a transformer because it cannot change the electromotive force of DC because the magnitude of the DC doesn't change. So, AC is used as its magnitude and polarity change.

22. We know, filament lamp converts only 10% of electrical energy to light energy but a fluorescent lamp converts 30% of electrical energy into light energy. So, a fluorescent lamp of 40W is better than a filament lamp of 40 W.

23. We know that neutral wire (earthing wire) carries the leaked current to the earth. If we touch the earthing wire also, the current flows to our body and returns to the wire, and goes to the ground to be neutralized. So, we don't feel shocked even if we touch a neutral wire.

24. We know that the birds don't touch the earth's surface while sitting on power lines. So, the current that flows to their body and flows back again to the wire. Therefore, the bird doesn't get any shock. Hence, birds are found sitting on high voltage transmission lines.

25. We know, inert gas doesn't take part in any reaction due to its stable state of electronic configuration. As a result, using its property, to avoid chemical reaction inside bulb even in extreme temperature inert gas is used to fill the electric bulb.

26. A thin and long tungsten wire is used in an electric bulb because it has very high resistivity and has a very high melting point. So, it doesn't melt even if the light bulb has a high temperature.

27. We know, nichrome is an alloy of nickel and chromium metals. It has high resistance and doesn't oxidize at very high temperatures. So, nichrome wire is used in an electric heater but not a copper wire.

28. We know, tungsten wire has low resistance and it cannot convert electrical energy to heat energy and also oxidize at high temperature. So, it is not used in the heater.

29. The core of a transformer should be laminated to minimize energy loss due to the production of an eddy current.