A parallel beam of light passing through a plane-parallel plate of thickness H with refractive index n is directed by a lens to the cathode of the photocell. The focal length of the lens F is significantly greater than its diameter D. The relative position of the Lens and the photocell is such that the round photocathode exactly blocks the light flux. In this case, the galvanometer in the photocell circuit shows the current I. What current will the galvanometer show if you place a plate between the lens and the photocell without changing the position of the latter?

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