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Explain Hallwachs’ and Lenard’s experimental observations. |
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Answer» Lenard observed that when ultraviolet radiations were allowed to fall on the emitter plate of an evacuated glass tube enclosing two electrodes (metal plates), current flows in the circuit. As soon as the ultraviolet radiation is stopped, the current flow also stops. Thus, light falling on the surface of the emitter causes current in the external circuit. Hallwachs observed that the uncharged zinc plate became positively charged when it is irradiated by ultraviolet light. Also positive charge on a positively charged zinc plate gets enhanced when it is illuminated by ultraviolet light. From the experimental observations he concluded that zinc plate emits negatively charged particles under the action of ultraviolet light. |
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