In your mind what is this roundabout above the train compartment? And what is its function? So let's know.

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When you are traveling in the train in the summer season,

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 you must have felt more heat inside than outside. 

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The heat increases when there is more population in the train.

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They are applied to control this heat.

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They are called roof ventilators. 

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These are used to remove heat or suffocation from the train compartment. 

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You must have seen in the box that there is a mesh inside to keep the gas out.

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