Kalashnikov surfing
Question: If I fire a gun at one of the buttons on my TV remote control, will
the remote have enough time to send a signal to change channel before it is
destroyed?
Answer: Modern electronics can operate extremely quickly, but not quickly
enough for this. Let鈥檚 assume the bullet is travelling at 500 metres per second
(bullets from some guns are faster, some slower) and a remote control button
travels 2 millimetres after being pushed before making the relevant electrical
contact, and can be pushed a further 4 millimetres before the printed circuit in
the remote control is damaged. These guesstimates help with the maths.
So, presuming the bullet hits the button perpendicularly, the time between
the electrical contact being made and damage to the remote control would be
0.000008 seconds (0.004/500) or 8 microseconds. It is true some modern
microprocessors could execute a few hundred basic instructions in this time, but
we have to create and transmit an infrared code before the transmitter is
destroyed. The Philips/Sony RC5 code that is commonly used in remote controls
takes 25 microseconds to transmit.
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You are just going to have to get out of that armchair!
John Childs
Esh Winning, Durham
Answer: Remote controls need to send a variety of commands to operate the
TV.
Each command is distinguished from the others by its code. These codes
consist of a series of infrared pulses, not unlike Morse code. The time it takes
for a complete code to be transmitted is short enough to give the impression
that changing channels is instantaneous, but the bullet will have ploughed
through the remote well before its transmission is completed.
It would be possible to construct a remote control system that didn鈥檛 use
time-based codes. The remote could transmit a different infrared frequency for
each command. This would require more expensive components and, worryingly, the
TV might change channel in response to any warm object in the room.
Even if this system were used, it would take time to detect a single
unmodulated frequency, so shooting the remote would probably still not work.
Paul Goodridge
Redhill, Surrey
Answer: Infrared TV remote controls wait a bit before transmitting after a
key press has been detected鈥攖his is called 鈥渄e-bouncing鈥�* and ensures that
the button has been pressed deliberately.
They then generate a coded sequence of on/off pulses to indicate the required
action. This sequence typically takes some milliseconds to complete and the
remote will have been disrupted by the bullet well before the complete code
sequence has been transmitted. Moreover, the infrared radiation from the muzzle
flash will reach and probably overload the TV infrared receiver before the
sequence has even started.
Perhaps your gun-toting enquirer should have several TVs running
simultaneously on different channels, and just pick off the ones with the
unwanted programmes on them. This should be quite satisfying, if a little
expensive.
John Elsbury
Auckland, New Zealand
*Switches (and even the buttons on your computer keyboard) tend to 鈥渂ounce鈥�,
that is, they generate multiple signals as the contacts get close to one
another. So they are de-bounced to ensure that only one signal goes through in a
short time period. This adds a delay that isn鈥檛 significant until you start
using firearms instead of fingers!鈥擡d.
Bathed in light
Question: I am studying the life of a well-known British statesman who was in
the habit of taking something called an 鈥渆lectric light bath鈥� in the years
before and after the First World War. What was this?
Answer: An electric light bath was a cabinet with a number of incandescent
lamps on the inner surface. The subject sat, or in some versions reclined, in
the cabinet with their head protruding. The light bulbs probably had carbon
filaments which emitted short-wave infrared radiation that heated the skin. The
temperature was controlled by varying the number of lamps switched on.
Spending time in a cabinet was considered therapeutic or, at least,
physically comforting, much like taking a hot bath without getting wet.
John Low
Thorpe Bay, Essex
Answer: The electric bath appears to have been invented by Dr J. H. Kellogg
of breakfast cereal fame, and a drawing of it can be found at
www.electrotherapymuseum. com/28.GIF.
I have a book called Medical Electricity by H. Lewis Jones,
published in 1906, which notes: 鈥淚t has been claimed that the light given out by
incandescent lamps has a therapeutic value above that of the heat they afford,
and the use of electric light cabinets in which the whole surface of the body is
exposed to the light of incandescent lamps has been very largely advocated and
pushed of recent years, especially by various interested persons . . .
If the extravagant claims made by certain writers be disregarded it still
remains that, for certain purposes, the use of this method of treatment is of
value, particularly in the treatment of stiff and painful joints.鈥�
The electric light bath was unusually harmless for a late 19th-century
medical appliance. The book also contains diagrams of several disturbing
electrodes used to apply high-frequency currents inside the body.
Adrian Cox
Oxford
This week鈥檚 questions
Skull splitter! Why do we have headaches? What are they?
Natasha Johnson
Castleford, West Yorkshire
Ancestral vinegar: During the Second World War we would often find a
jelly-like substance in our vinegar bottle. My mother called it
鈥渕other-of-vinegar鈥�. Is it true that if you put this into water it will turn
into vinegar? Why don鈥檛 we see it any more?
M. O鈥橞yrne
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