# Homework Help: Geometrical Optics (lens and refraction)

1. Apr 17, 2013

### songoku

1. The problem statement, all variables and given/known data
1. A cylindrical tank 2.4 m deep is full to the brim with water. Sunlight first hits part of the tahnk bottom when the rising maes at 22o angle with the horizon. Find the tank's diameter

2. An aquarium is made from a thin-walled tube of transparent plastic 50 cm in diameter. If we are looking directly into th aquarium, what is the apparent distance to a fish 15 cm from the aquarium wall?

2. Relevant equations
n = c / v

n1sin i = n2 sin r

n = real depth / apparent depth

3. The attempt at a solution
1. I can't imagine the situation and I don't understand this part :"Sunlight first hits part of the tank bottom when the rising makes at 22o angle with the horizon."

2. The shape of the aquarium is cylindrical? I don't know what the diameter is used for.

2. Apr 17, 2013

### rude man

I'm befuddled too. The poser seems to have ESL.

In part B are we looking "directly" thru the wall or from atop the aquarium?

3. Apr 17, 2013

### songoku

What is ESL?
That's also the thing that I don't know. But let us take both cases:
a. we are looking from the top of aquarium --> we don't know the real depth so how can we find the apparent depth

b. we are looking directly through the wall --> no idea how to do it

4. Apr 17, 2013

### rude man

English as Second Language.

Me neither. Don't understand the question at all.

5. Apr 18, 2013

### Basic_Physics

Sunlight refracted to just reach the bottom of the tank.

#### Attached Files:

• ###### sunlight into tank.jpg
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6. Apr 18, 2013

### songoku

Oh it is actually pretty easy. Just use the snell's law to find the angle of refraction and use tan to find the diameter.

Can you help me with the second one too?

Thanks

7. Apr 19, 2013

### Basic_Physics

Fish in tank

Refraction at the wall of the tank.
The apparent depth decreases due to the refraction of the light at the water-air interface.

#### Attached Files:

• ###### fish in tank.jpg
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8. Apr 21, 2013

### songoku

Thanks a lot for your help