In quantum mechanics, if the energy of the particle, E, is less than the energy required to enter a region, U, the particle is always reflected back.

The tunnel effect is when an object, usually an elementary particle, passes through a potential barrier even though it doesn't have enough energy to overcome the barrier. In quantum mechanics, the tunneling effect is when particles pass through a potential barrier even if the particle's total energy is less than the barrier height.

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Engineering Physics Practice Test: Quantum Physics - Zeeman Effect 

Engineering Physics Practice Test: Quantum Physics - Raman Effect