# Why is a bulb lit as soon as a torch is switched on?

• koat
In summary, the bulb is lit as soon as the torch is switched on because the vibrations caused by the voltage create heat which quickly heats the filament to white hot. The electrons might move relatively slowly, but the wire is already full of them, so once the first ones start to move, a pressure wave moves through the wire (at the speed of light) causing all of them to start moving very soon.
The vibrations they cause as they drift under the influence of the voltage creates heat which quickly heats the filament to white hot.

The electrons might move relatively slowly, but the wire is already full of them, so once the first ones start to move, a pressure wave moves through the wire (at the speed of light) causing all of them to start moving very soon.

For the same reason, water starts pouring out of your faucet almost instantly after you turn it on.

Addendum: Imagine a street full of crowded people milling around. Someone yells Free Beer! from one end of the street creating a desire to move in one direction. They're crowded so they don't move quickly but their bustling and bumping into each other will cause quite a loud ruckus quite quickly. The light from the filament is the electrons yelling for free beer as they bump along. ;)

You could also think of it in terms of marbles in a tube. Where the marbles represent electrons and the tube represents the wire. If you push a marble in one end of the tube, another marble will come out the other end almost instantaneously. Even though the marbles are actually moving very slowly, the force moves from one to the other with great speed. It's the same in a wire. Even though the electrons are only moving at 0.03miles/hr, the wave fronts are moving much, much faster.

jambaugh said:
Addendum: Imagine a street full of crowded people milling around. Someone yells Free Beer! from one end of the street creating a desire to move in one direction. They're crowded so they don't move quickly but their bustling and bumping into each other will cause quite a loud ruckus quite quickly. The light from the filament is the electrons yelling for free beer as they bump along. ;)

Now that clears it up!

## What causes a bulb to light up when a torch is switched on?

When a torch is switched on, the electrical circuit is completed and current flows through the bulb. This causes the filament inside the bulb to heat up and emit light.

## Why does a bulb light up immediately when a torch is turned on?

There is no delay in the bulb lighting up when a torch is turned on because electricity travels at the speed of light, so the current reaches the bulb almost instantly.

## Why does a bulb only light up when a torch is switched on and not when it is off?

When a torch is switched off, the electrical circuit is broken and there is no flow of current. This means that the filament in the bulb does not heat up and there is no light emitted.

## How does the battery in a torch affect the lighting of a bulb?

The battery in a torch provides the energy necessary to power the bulb. When the switch is turned on, the battery supplies the current needed to heat up the filament and produce light.

## Is it possible for a bulb to not light up even when a torch is switched on?

Yes, it is possible for a bulb to not light up when a torch is switched on. This could be due to a faulty bulb, a loose connection, or a depleted battery. It is important to check these factors before assuming that the torch itself is the issue.

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