Electric Bulbs - Class VII

Electric Bulb is a source of light. Hence above statement is False.

tungsten has a high melting point and is able to withstand heat and corrosion. Tungsten is one of the most durable types of filaments used in light bulbs. It must be exposed to very high temperatures before melting, and only carbon arc has a higher heat resistance level than tungsten.

Electric bulb uses the  heating effect of current.when current is passed, electric bulbs has a tungsten filament which gets heated with the flow of current and brighten up, the filament having a high value of resistance heated up , more the heat more will be the light.

Daily energy: 10×40×5/1000 = 2 kWh (bulbs), 5×100×8/1000 = 4 kWh (fans), 1×1×1 = 1 kWh (heater). Total daily = 7 kWh. Weekly = 49 kWh. Cost at Rs 5/unit = Rs 245. Option C asks for the cost of consumed energy.

$100W$ means $100J$ of energy is consumed per second of time.

Because atoms and molecules can exist only in certain specific energy states, the energy emitted by the excited molecule is limited to differences between these states. Only certain energies of light are emitted. The colour of the glow is determined by the energy of the emitted light. and for argon its bluish

Incandescent light bulbs use heat generated by the resistance of the filament to create light. to get white light you need the filament to reach 2700-3300 K to give off white yellow light.

The reason tungsten is used is because it has the highest melting temperature of any element at 3600 K.

To generate a lot of heat you need a big resistance. Resistance(R) is dependent on resistivity ($\rho$) but also on the length (l) of the wire and the width (w).

Having a big resistivity helps to create a big resistance but since you can change the thickness and length of the filament in light bulb (the filament is looped to increase the length) you can control the resistance. 

Incandescent light bulbs are filled with an inert gas like nitrogen, argon, or krypton - so that the filament doesn't catch fire. Early ones were a vacuum. Flourecent lamps are filled with an inert gas plus mercury vapour or neon, which glows ultra-violet when charged. The inside of the bulb is painted to give it colour.

The filament of bulb has high resistance so the filament heats up due to current passing through (${ I }^{ 2 }R$ losses )  and due to its heating , the electrons change their energy states and photons in visible spectrum are emitted . more the losses , more would be the light.that's why filament of bulb offers high resistance.

The leading wire is usually made with conductors such as copper and aluminium, therefore have less resistance than the filament which is usually made with tungsten and has a high resistance.
Due to this the power lost P $ =I^{2}R $ is greater for filament which is visible as light(and also heat).

Filaments in incandescent light bulbs are made of tungsten. When electric current goes through the filament, the filament glows. It may also be known as the electron emitting element in a vacuum tube. To make the bulb produce more light,the filament is usually made of coils of fine wire, also known as the coiled coil.

Tungsten metal is selected for making filaments of lamp bulbs because tungsten can sustain high temperatures and it has high melting point, combined with the fact that it also has high resistivity. They do not oxidize easily at high temperatures.

Resistance of 25 w bulb, ${R _1} \Rightarrow \frac{{{{220}^2}}}{2} = 1936\Omega $