# Interesting Question of the Day – 19 December 2018

Someone did the math on the cost of using turn signals.

If petrol costs $1.30 per litre, you use your turn signals 20 times per day for 10 seconds each time, and you have 10 watt LED bulbs, what is the annual cost?

Is it 5 cents, 50 cents, $5, or $50?

Note: We’re just talking the cost in petrol, not the cost of replacing burned out bulbs.

The first new player to comment on the website with the correct answer wins a free drink at their next iQ Trivia show.

5 cents per year is the closest figure and the exact number depends on the efficiency of the engine.

20 times/day x 10 seconds x 10 Watts gives 2000 Joules/day or 730000 Joules/year (0.73 MJ/year)in a non leap Year.

The calorific value of petrol is 45.8 MegaJoule/kg or about 37 MJ/litre.

If we assume the engine and generator are 30% efficient we will consume 0.73/(37 x 0.3) = 0.066 litres per year or 8.6 cents.

It is a cheap way to improve your chances of surviving!

Leave it to the engineer to calculate it this way.

And yes, a lot depends on the minutiae of energy efficiency, but it is certainly worthwhile.