Nvm, I'll just wait around rather than sound so stupid.

Originally Posted by Faer

Thank you so much! That was really helpful, and just made me realized how unprepared I am...gah. -.-

Anyhow. I'll be pouring in with questions throughout today for the next...howsoever many hours it is till the exam. XD

1)A certain crude oil has an index of refraction of 1.26. A ship dumps 1.17 m3 of this oil into the ocean, and the oil spreads into a thin uniform slick. If the film produces a first-order maximum of light of wavelength 509 nm normally incident on it, how much surface area of the ocean does the oil slick cover? Assume that the index of refraction of the ocean water is 1.35.

I can't figure out the relation between n and thickness. :/

1) phase difference = 2nt. For constructive interference, PD = mλ. Take m = 1

Therefore, you have λ = 2nt. Rearranging for t, you get: t = λ/(2n). Substitute your knowns and you get the thickness.

Now, recall that volume = area x height. Rearrange for area gives: area = volume / height (where height is the thickness).

Thus, area = volume / thickness.

Originally Posted by Faer

2) Determine the minimum thickness of a soap film (n = 1.350) that will result in constructive interference of the red Hα line (λ=656.3 nm);

For 2, at first, I tried t = λ/(2n) (same as above) but it was the incorrect answer.

Next, I tried t = λ/(4n), and it worked. I have no idea why though, so if someone could enlighten me, that would be great!

I couldn't find that formula in the textbook at all! This is so weird...thanks for the help.

Originally Posted by Faer

I couldn't find that formula in the textbook at all! This is so weird...thanks for the help.

It's on the formula sheet. Here!

Originally Posted by ShesTheMan

Yes it is, the options are:
a) 24.2 ± 0.5 m/s
b) 24.25 ± 0.04 m/s
c) 24±1m/s
d) 24.25 ± 0.53 m/s
e) 24.2 ± 0.02 m/s

Ok, so when you're dealing with uncertainties, and particularly uncertainties of functions, your best bet is to use differentiation.

So for this question, you should know that solving for final velocity (Vf) should yield the equation:
Vf = sqrt(2*a*h) = (2*a*h)^1/2
[this comes from the kinematic equation Vf^2 = Vi^2 + 2*a*h, and your Vi = 0]

Now, to get uncertainties from complex functions, you must solve for the derivative of your equation and multiply it by the uncertainty of your variable (you can find this definition on page 84 of your 1b03 lab manual):
Vf = (2*a*h)^1/2
Vf' = 1/2(2)(2*a*h)^-1/2 (uncertainty of a*h)
Vf' = (2*a*h)^1/2 (uncertainty of a*h)

--> the absolute uncertainty of a*h = ah [(delta a/a) + (delta h/h)]

After plugging in all of the numbers, I get 24.3 +/- 0.5

The only thing I'm unsure about is the constant and whether that plays a factor in the absolute uncertainty of a*h. Other than that, I'm pretty sure this method is correct. Please feel free to correct me if I'm wrong.

Could someone also explain #5 on the second practice exam to me.. I don't quite understand why the answer is what it is. :$

A factory worker raises a 100. kg crate at a constant rate using a frictionless pulley system, as shown in the diagram. The mass of the pulleys and rope are negligible.
With what force is the worker pulling down on the rope?

The answer is 490 N.

Originally Posted by ShesTheMan

Could someone also explain #5 on the second practice exam to me.. I don't quite understand why the answer is what it is. :$

A factory worker raises a 100. kg crate at a constant rate using a frictionless pulley system, as shown in the diagram. The mass of the pulleys and rope are negligible.
With what force is the worker pulling down on the rope?

The answer is 490 N.

Ok, so the weight of the object is 980 N. Since there are TWO strings pulling up on the object, the tension in each string must be half of that (which gives you 490 N).

Stupid question time! Where are the practice exams posted?!

Originally Posted by Faer

Stupid question time! Where are the practice exams posted?!

http://www.physics.mcmaster. ca/phys1b03/

Click on "Old Tests and Exams" on the left menu.

*sigh*

I knew I should have checked there...grrr. Thanks!

Help with this question as well :$
A hot air balloon is kept from floating away by cables which hold it to the ground. The mass of the balloon and the air inside the balloon is 2340 kg. The density of the hot air inside the balloon is 0.960 kg/m3, while the density of the air outside the balloon is 1.21 kg/m3. When the rope is cut, the balloon accelerates upward at a rate of 1.23 m/s2. What is the volume of the balloon (in units of m3)?

A. 1690
B. 2180
C. 2438
D. 2740
E. 8190
F. 10,500

Ans is B.

I'm getting 2131 which is close.. but not quite the ans.

i don't get this question at all, help would be awesome
http://i.imgur.com/LtAB2.png

Hey. Hope studying has been going well for everyone.

Just wondering, does everyone have all their marks up?
A few of mine say 'Not yet public': Lab Total, Class, and of course, Final Exam.

Just wondering if it's only me... or if this is the case for everyone....

I believe the class marks aren't up for anybody, though my prof said they should be. >:( (Karen Hughes posted that they wouldn't be).

As for Lab Total...I'm not sure...