# Difference between revisions of "ME/CS 132a, Winter 2010, Homework 1 FAQ"

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== Problem 1 == | == Problem 1 == | ||

* It looks like the units don't exactly cancel out in the exponential term in the Planck's law. Is this supposed to happen? | * It looks like the units don't exactly cancel out in the exponential term in the Planck's law. Is this supposed to happen? | ||

** '''Answer:''' | ** '''Answer:''' If you are using the old slides from lecture 2, the correct unit for the Planck constant is J·s, or W·s<html><sup>2</sup></html> (but everything else is correct). The revised version has corrected this typo. [Shuo] | ||

== Problem 2 == | == Problem 2 == |

## Revision as of 06:20, 14 January 2011

## Problem 1

- It looks like the units don't exactly cancel out in the exponential term in the Planck's law. Is this supposed to happen?
**Answer:**If you are using the old slides from lecture 2, the correct unit for the Planck constant is J·s, or W·s<html>^{2}</html> (but everything else is correct). The revised version has corrected this typo. [Shuo]

## Problem 2

## Problem 3

- Do we have to show that the focal length is equal to R/2/(n-1)?
**Answer:**No, you don't. [Shuo]

- Can we use the fact that the index of refraction of a vacuum (and approximately the index of refraction of air) is 1?
**Answer:**You can assume that the refractive index of the air is 1 when deriving the thin lens equation, but the first part (showing the ray is not refracted if it passes the center of a thin lens) shouldn't depend on this. [Shuo]