A glass lens of refractive index 1.5 is placed in a trough of liquid. What must be the refractive index of the liquid in order to mark the lens disappear?

Explanation

To solve the problem of determining the refractive index of the liquid required for the glass lens to become invisible, we can follow these steps:

### Step 1: Understand the Concept of Refraction
The phenomenon of refraction occurs when light passes from one medium to another, and the bending of light depends on the refractive indices of the two media involved. For an object to appear invisible, the refractive index of the surrounding medium must match that of the object.

**Hint:** Recall that when two materials have the same refractive index, light does not bend at the interface, making the object appear invisible.

### Step 2: Identify the Refractive Index of the Glass Lens
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