A potential barrier is a region within which the potential energy of a particle is much higher than its immediate surroundings. When the wave function encounters a potential barrier whose height is greater than the total energy of the particle , the amplitude of the wave function does not become zero abruptly but decreases exponentially . This means that the wave amplitude is non zero beyond the barrier and hence there is probability of finding the particle beyong the barrier .This process is called quantum tunneling.
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