When any element absorbs energy by any external source as heat or electricity, it emits radiations, these radiations while passing through a prism produces different types of images on screen called emission spectrum. There are following two types of spectrum.
When any white light from sun or any incandescent lamp passes through a prism, it deviates and also splits into a bond of seven colours. This process is called dispersion while the bond of colours obtain on screen is called continuous spectrum. On one end of spectrum least deviated violet colour is obtain. These are demarcation between the colours present in such spectrum.
When electricity passes through any gas at low pressure some radiations emitted from the gaseous source which when passes through a prism, some discrete sharp lines are obtained called line spectrum.
Observation indicates that radiations produces by different gaseous source produce lines of different wavelength on the source as line spectrum therefore, use for the identification of elements.
FACTS ABOUT LINE SPECTRUM
i. The wave lengths of radiations are same in the case of samples of same elements.
ii. Under right conditions only certain wave lengths are emitted by any one element.