Power is only useful to scientists & engineers; no one else

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

29 May 2016

If you are not a scientist or an engineer, then power is a totally useless quantity to you. Still, manufacturers flash it around in an effort to make their products look more attractive. Take motorcars, for example… I saw a large billboard along Uhuru highway in Nairobi depicting a car flying and leaving behind a trail of fire! The advert proclaimed in bold letters: “198kW”.

What does that number mean to the ordinary motorist? Answer: absolutely nothing! It does not tell you how quickly the car accelerates; not how fast it can move; and not how much load it can pull!

Still; an interesting question comes to mind…the power of cars is normally given in “horse-power”: why is this one show in kilowatts (kW)? I don’t know, but in case you are wondering, one kilowatt is approximately equal to 1.34 horsepower. So, 198kW is about 265hp.

The crucial piece of information missing from this billboard (and nearly all other car adverts) is the mass of the vehicle. Without it, there is really no point in stating the power. Have you ever noticed that when your car is heavily laden, it accelerates sluggishly and cannot reach very high speeds?

Motorists should be more concerned about acceleration data than the power figures. This is usually given in terms of the number of seconds it takes the car to reach 100km/h. After all, this is something you can confirm for yourself easily during the test-drive. Power? You’d have to take the car to a laboratory…but wait, you’re not a scientist, are you?

Another area where manufacturers are fond of giving power figures is in music systems. Now everyone knows that the loudness of sound is measured in decibels; so why do they bombard us with those useless power figures?

I don’t know; but the crucial piece of information that is never given is the efficiency of the loudspeakers. That is, how many decibels are produced from each watt of power? Without that, you cannot tell how loud the music system will be.

Music system manufacturers have extended their creativity on power figures to the point of becoming laughable: if you burst out laughing, you are likely to produce more sound than a domestic audio system labelled 1,000 watts!

Finally, there is the humble lightbulb. For many decades, the only type available was the hot-filament one. So manufacturers got used to stating the number of watts consumed in heating the filament.

But the brightness of light is not expressed in watts: it is stated in lumens – a word derived from “luminous”. Thankfully, lightbulb manufacturers do indicate the number of lumens that their products produce: only that the figures are in very small print.

As new types of bulbs come into the market, their brightness is being expressed in relation to the old filament type. Thus a 12W fluorescent bulb is said to be as bright as a 60W ordinary one. This is because both produce about 800 lumens of light. Clearly though, knowing the power isn’t much help at all.