Question Corner

Drip reduction

QUESTION: Why does water from a tap, when adjusted to a trickle, reduce, to a drip after a couple of minutes?

ANSWER 1: Flow through a partly open tap reduces because the washer, which was compressed while the tap was closed, re- expands.

When you want to stop a flow, you have to close the channel completely. It is very difficult to do this by bringing two hard surfaces together.

Perfectly flat surfaces are expensive and difficult to produce, and if there is any debris in the water such as loose scale from the pipes, it will spoil the seal that forms between them.

Placing a rubber washer between the faces avoids these problems, as it doesn't need to be completely smooth.

The washer is squeezed between the faces and forms a seal around any particles and irregularities, completely shutting off the flow.

If you partially open the tap, the initial flow of water diminishes as the washer re-expands to its natural size — the size it was before being compressed. Perfectly explicable, but still an irritation.

ANSWER 2: In the case of gas, taps normally seal by metal-to- metal contact, often in the form of a conical plug, so the effect cannot be explained by a sealing washer expanding.

A gradually reducing flow of gas may be seen when the pipe between the gas tap and the gas jet is long or wide. If the tap is wide open and is turned to a lower setting, there will still be pressure in the pipe between the tap and the jet. This means the flame will shrink as the flow settles down to the new pressure.

New Scientist

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Aquarium maintenance

QUESTION: Is it necessary to change the water in an aquarium periodically?

Rajesh, Chennai

ANSWER: Like all other creatures fishes too need oxygen for breathing. But unlike other creatures fishes respire by their pair of gills. Their gills separate the oxygen from water and release out carbon-dioxide.

In a lake or pond there is not much considerable change in the Oxygen level because:

In a huge amount of water only negligible ratio of oxygen is used. Direct and indirect rainwater keeps the oxygen ratio stable.

Water plants like Hydrilla and Vallisneria use the carbon-dioxide and deliver oxygen during their photosynthetic activity.

But in the aquarium there is less amount of water and there are no natural plants to maintain the oxygen level.

Another reason for changing the water is to keep the water clean from the fish waste in aquarium.

S. Ragunathan, Pudukottai

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This week's questions

Why does one feel hungry soon after studying?

V.V. Balasubramanyam, Anantapur, A.P.

What is the reason for the coloured rain and vanishing of wells especially in Kerala?

Ashok Ramasamy, Cuddalore, T.N.

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