Physics
The device used for measuring the wavelength of X-rays is

Bragg Spectrometer
G.M. Counter
Mass Spectrometer
Cyclotron

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Physics
Lightning is produced when

Clouds strike against impurities in air and the friction burns up these impurities
Water vapour produces electricity in the clouds
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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