Physics
Fibre optics work on the principle of

Optical rotation
Total internal reflection
Scattering of light
Total internal absorption

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Physics
Lightning is produced when

Water vapour produces electricity in the clouds
Clouds strike against impurities in air and the friction burns up these impurities
Strong opposite charges in different clouds break down the resistance offered by the intervening air
Similar charges of electricity rush towards each other and then get repelled

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