Lighter spark
Why is the spark from a gas lighter blue in colour?
K.R. Inesh, V.V.N.K.M. Sr. Sec. School, Vellore, Tamilnadu
The gas lighter works on the principle of the piezo-electric effect (conversion of mechanical stress into electric signal). Inside the gas lighter, a piezo-electric crystal is placed, at one end of a spring whose other end is connected to a wired hammer inside the cylindrical lighter. The arrangement is made in such a way that when we press the lighter, the hammer gets pushed, hitting the piezo-electric crystal and resulting in a high voltage (800 volts) electric discharge in the small gap between two metallic points placed at the lighting end. The air present in this small gap gets ionised and offers the path for the electric discharge. This discharge is the spark that ignites the combustible gas of the gas burner. Normally lead zirconate titanate crystals are used as the piezo-electric ceramics in gas lighters due to their low cost and high sensitivity.
The colour of the spark depends on the nature of the gas present between the metal points. If it is helium, it will be red in colour and sodium gas gives bright yellowish-orange colour. In our household gas lighters the small gap is occupied by the surrounding air. Since air is mostly made of nitrogen, it is nitrogen that makes up the path of the electric discharge, burning with a blue flame. Hence household gas lighters give out a blue spark.
Dr. T. Bhavani, Bengaluru
This week’s questions
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Abhishek Pathak, Chennai
Why does a room look small when painted with a dark colour and comparatively bigger when painted with a light colour?
Sruti Sridhar, New Delhi
When we place a white paper under sunlight for some days, the colour of the paper changes from white to pale yellow. Why is it so?
Arshad.M, Malappuram,Kerala
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Dinkar Drona, Chennai
