Một chậu có thành dày bằng thủy tinh chiết suất 1,5 đựng một lớp nước và một lớp benzen (nhẹ hơn nước và không tan trong nước). Chiếu một chùm tia đơn sắc hẹp qua hệ và bố trí để chùm tia ló ở đáy chậu được ra ngoài không khí. Vẽ đường đi của chùm tia sáng qua chậu và chứng minh chùm tia ló song song với chùm tia tới, biết chiết suất benzen là 1,5.

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