# Geometric Questions

1. May 9, 2010

### fl415

the questions is
The left end of a long glass rod in diameter has a convex hemispherical surface in radius. The refractive index of the glass is . Distances are measured from the vertex of the hemispherical surface (to the right is positive for image distances).

Determine the position of the image if an object is placed in air on the axis of the rod at the infinitely far distance to the left of the vertex of the curved end.

do i use 1/d+1/d_i=1/f??? or i use something else? i plug in 1/d which d is infinity, so its 0, but i didnt get the right answer. can anyone help?

2. May 9, 2010

### rl.bhat

Use the formula
1/do + 1/di = (μ - 1)/R

3. May 9, 2010

### fl415

its still wrong, i plug in 1/d_i=(1.6-1)/3 which give me 5 and its wrong. you got any other ideas?

4. May 9, 2010

### fl415

the question is

The left end of a long glass rod 6cm in diameter has a convex hemispherical surface 3cm in radius. The refractive index of the glass is 1.6 . Distances are measured from the vertex of the hemispherical surface (to the right is positive for image distances).

i dunno why it didnt show up number at first

5. May 9, 2010

### rl.bhat

What is the radius of curvature of the hemisphere? What is the expected answer?

6. May 9, 2010

### fl415

its 3 cm,the answer expected in cm

7. May 10, 2010

### rl.bhat

Then f is 5 cm.

8. May 10, 2010

### fl415

f is 1.5......right? its radius /2

9. May 10, 2010

### rl.bhat

No. f = r/2 is true for the concave mirrors only, not for the spherical surfaces.

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