ÐÓ°ÉÔ­´´

Q: I have twice driven through the end of a rainbow where it meets the
ground, although I am told this is impossible. I was surrounded by the
rainbow’s colours and there were many other drivers to witness that it can
happen. Can anyone explain this?

(continued)

* * *

A: Malcolm Brooks of the Met Office states that this experience is impossible
(18 June), but is it really so rare to find the end of a rainbow? I walk
to work past the fountains of the Serpentine in Kensington Gardens in London,
and on two separate occasions have observed the end of a rainbow. There
was, however, demonstrably no pot of gold there.

Barry Rigal London

A: On 7 April 1994, following a storm, I was driving east from Swindon
to Reading. A rainbow had formed and appeared to end in the middle of the
road ahead. I placed a camera on the dashboard and made a number of exposures,
up to a point where I appeared to drive through the end of the rainbow.
If this is impossible, what is happening?

Dennis Mackie, Maindenhead, Berkshire

Shocking TV

Q: After switching off a television in the dark why, when the screen
is touched, does static electricity discharge through the body and the screen
fluoresce at the point touched?

A: The final anode of the television’s cathode-ray tube (CRT) is formed
by a thin layer of aluminium coating the front part of the inside of the
CRT, including the back surface of the screen. When the tube is operating,
this anode is charged to bewteen 25 and 30 kilovolts and it induces a charge
of similar magnitude on the outside of the tube you can feel this because
it makes the hairs on your arim stand up and align themselves with the field.
If you put your hand close enough to the screen, you will hear a crackle
as the screen discharges. The amount of charge involved is tiny, so you
should not feel a shock

By the time the TV is switched off, most of the charge on the outside
surface of the glass has leaked away, os an opposite charge is induced when
the field is removed. This can be discharged in the same way buy, since
the set is now off, the rapidly changing electrical field can be seen to
have an effect on the screen phospher. The phosphor is excited and glows,
just as it does when struck by the fast-moving electrons which create the
television picture. The same effect is used in electronluminescent panels
(the sort that provide the back lighting for liquid-crystal display screens
on portable computers). The phosphor can also be excited by light – try
experimenting with an electronic flash.

Mike Brown, Nashville, Tennessee, US

This week’s questions

Inner glow: During a nocturnal walk in the woods of the Belgian Ardennes
I found a piece of rotten wood. To my surprise, I saw a soft glow inside
As I write this, after 24 hours in darkness, the wood is still glowing What
causes this.

Erik Aerts, Nuth, the Netherland

Bubbly character: Do the bubbles that form when washing with soap or
detergent actually play a part in the cleaning process? Do the items being
washed get cleaner the more bubbles there are?

Johan Hjelm, Uppsala, Sweden

All at sea: I stood at the foot of a lighthouse, on a 15-metre high
cliff, looking out to sea. It was a generally clear night with a light sea
mist and visibility was around 6 kilometres. The beam of light, which was
rotating clockwise overhead, appeared t me to be coming from a phantom lighthouse
on or near the horizon, and rotating anticlock wise (it was in time with
the actual beam). Any explanations?

J R Christie, Coventry, Warwickshire

Gust quest: What mechanisms are responsible for causing the wind to
blow in gusts?

Chris Long, Sussex

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