The flow of electrons in a definite direction iscalled current electricity.

i. Open electric circuit:
An electric circuit in whichno current is flowing is called an open circuit.

ii. Closed electric circuit:
An electro circuit in whichelectric current is flowing continuously is called aclosed electric circuit.

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.

The wire which produces heat by passing acurrent through it is called the heating element.

The current which changes its magnitude and polarityis called AC.

The current that has fixed magnitude and polarityis called DC.

The frequency of current distributed in Nepal is 50 Hzmeans the polarity of the current changes 50 timesin a second.

The process of producing current in a closed coil dueto the relative motion between magnet and coil iscalled electromagnetic induction.

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

When the current is passed through a wire of highresistance which becomes extremely hot and produceslight which is called the lighting effects of an electriccurrent.

When the current is passed through the wire ofhigh resistance, it becomes extremely hot andproduces heat which is called the heating effect ofan electric current.

When a current is passed through a wire, itproduces a magnetic field around it which is called themagnetic effect of an electric current.

fig. Electric bell

An electromagnet is made by using a cylindrical formof an insulated copper coil havinga large number ofclose turn is a solenoid.

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

A current-carrying wire exerts a force on amagneticcompass and defects it from its usual north-southposition which is called the motor effect.

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

A transformer is a device that converts high voltageAC to low voltage AC of the same frequencyand viceversa The function of the step-up transformer is that itconverts the low voltage of current to high voltage.

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

A battery charger is a device that is used to putenergy into a secondary cell or rechargeable cell byforcing an electric current through it.

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

An inverter is an electric device that changes AC intoDC and vice versa.It is used to convert AC source to DC source orDC source to AC source.

a. Live wire and neutral wire.

b. AC and DC.

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

We know, electric current flows from phone wire to thepower load. So, to disconnect or block the current rightat phase wire during the case of overload, a fuse isconnected to a phase wire.

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

We know, filament lamp converts only 10% of electricalenergy to light energy but a fluorescent lamp converts30% of electrical energy into light energy. So, afluorescent lamp of 40W is better than a filamentlamp of 40 W.

We know that neutral wire (earthing wire) carries the leakedcurrent to the earth. If we touch the earthing wirealso, the current flows to ourbody and returns to thewire, and goes to the ground to be neutralized. So, wedon't feel shocked even if we touch a neutral wire.

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

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

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

We know, nichrome is an alloy of nickel and chromiummetals. It has high resistance and doesn't oxidize atvery high temperatures. So,nichromewire is used in anelectric heater but not a copper wire.

We know, tungsten wire has low resistance and it cannotconvert electricalenergyto heatenergyand also oxidizeat high temperature. So, it is not used in the heater.

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

The transformer is a device that increases or decreases the voltage of the alternating current. As the voltage of current produced in powerhouse is generally low, without the use of a transformer it cannot be made high to transmit current through long distances.