Why does refractive index reverse for light returning through a spherical surface?

[stpmmaths]

Homework Statement

Homework Equations

The Attempt at a Solution

I was kind of confuse with the use of refractive index.

For the first part of question, n₁ = 1.00 and n₂ = 1.50. From what I know, the object is at vacuum so the n₁ = 1.00.

But why for the second part of the question, n₁ = 1.50 and n₂ = 1.00 ? After the first refracting surface, the image should be at the vacuum too. But why we use n₁ = 1.50?

 

[tiny-tim]

Welcome to PF!

Hi stpmmaths! Welcome to PF!

I was kind of confuse with the use of refractive index.

For the first part of question, n₁ = 1.00 and n₂ = 1.50. From what I know, the object is at vacuum so the n₁ = 1.00.

But why for the second part of the question, n₁ = 1.50 and n₂ = 1.00 ? After the first refracting surface, the image should be at the vacuum too. But why we use n₁ = 1.50?

(I can't see your attachment yet, but …)

I assume that the light starts by going into the sphere from the air (or vacuum), so it's going from n = 1 to n = 1.5;

then it travels through the sphere (n = 1.5) until it hits the opposite surface and comes out again, so it's going from n = 1.5 to n = 1.

 

[stpmmaths]

Hi stpmmaths! Welcome to PF! (I can't see your attachment yet, but …)

I assume that the light starts by going into the sphere from the air (or vacuum), so it's going from n = 1 to n = 1.5;

then it travels through the sphere (n = 1.5) until it hits the opposite surface and comes out again, so it's going from n = 1.5 to n = 1.

Ok..I understand a bit.

Now I came across with another question similar to this question(quite similar)

Quenstion:

Answer:

Why the n₁ is 1.50 if we say the light starts from vacuum?

 

[tiny-tim]

Why the n₁ is 1.50 if we say the light starts from vacuum?

Because the light starts from the coin, inside the sphere, not from vacuum.

 

[Redbelly98]

Why the n₁ is 1.50 if we say the light starts from vacuum?

Look carefully at the arrows in the figure. Where do they start from?

EDIT: to clarify, look at the interface where the two rays meet. The ray arrows indicate they go from the glass into the air.

p.s. Hello tiny-tim!

 

[stpmmaths]

Oo, I got it.
Thanks everyone.