# Recent content by Steve Drake

1. ### Understanding the physical meaning of multiplication, etc

Hi BvU, Thanks for your reply. Your answers really shone some light on this. I want to be able to understand the 'steps' used in derivations, and what they mean physically, why they are done, and how you 'know' what to do and when to do it... In terms of going back to elementary level, I find...
2. ### Understanding the physical meaning of multiplication, etc

Is there some kind of intuitive way to understand the physical meaning when mathematical operations are applied to equations in physics? What I mean is that, say we start with a 'starting point' equation, in this example Ficks law of diffusion (wikipedia:): J = -D \frac{\delta \phi}{\delta x}...
3. ### Optical microscopes and white light / laser light

Hi Courtney, Andy, thanks for your replies. Some questions, I am not 100% familiar with this term, is optical microscopy widefield imaging? By laser light I meant very high temporally and spatially coherence lasers. I thought speckle only comes from a coherent source interacting with a random...
4. ### Optical microscopes and white light / laser light

I have a few questions regarding an optical microscope and their white light sources... So white light generally first hits a diffuser, some kind of ground glass lens. What is the purpose of this? Then the light goes through a field diaphragm, which we can open and close. I have heard that...
5. ### Newton's second law dp/dt version?

Thanks guys, forgot about the chain rule for differentiation. So in general, whenever there is a \frac{d^{2}}{dx} then it can be thought of two separate derivatives, each giving their own result. But the ^2 means it skips the first result and we go right to the second?
6. ### Newton's second law dp/dt version?

Hello, I am confused by the momentum version of newtons second law... So we know \bar{F}=m\bar{a}=m\left(\frac{d\hat{v}}{dt}\right) and that \bar{\rho}=m\bar{v}=m\left(\frac{d\bar{x}}{dt}\right) so is \frac{d\bar{p}}{dt}=m\frac{d\left(\frac{d\bar{x}}{dt}\right)}{dt} What I mean is this...
7. ### Schlieren Imaging / wave optics

The knife edge is just there to flatten out the transfer function. Without the knife edge the technique is known as shadography. In shadography, the samples refractive index inhomogeneities can be thought of as diffraction or phase gratings, causing the incident beam to diffract. The diffracted...
8. ### How to Fourier transform this expression?

I have this expression: f(\tau) = 4 \pi \int \omega ^2 P_2[\cos (\omega \tau)] P(\omega) \, \mathrm{d}w \quad [1] where P_2 is a second order Legendre polynomial, and P(\omega) is some distribution function. Now I am told that, given a data set of f(\tau), I can solve for P(\omega) by either...
9. ### Why does a light blinking quickly average out as 'on' to us?

Consider a light, an L.E.D for example, turning on and off once per second. For humans, we will look at it and think "clearly on, clearly off, clearly on, clearly off" for each 'state'. Our view of whether it is on or off will continue like this if its 'blink frequency' is increased up to a...
10. ### Inverse Problems in Scattering

Hi mate, thanks for the reply to my very old topic hah. I had a go at that cause the original CONTIN is too complicated for me to use. rILT seems to work but its very slow. I have been using other methods in the mean time. Thanks.
11. ### Is the current a kind of circulation?

A bit off topic, but where did you get that animation from? Its awesome! Thanks
12. ### How can I think of rotational diffusion inverse seconds?

Hi, Thanks That makes a big more sense... So in a geometrical sense... if a rod's center of mass with fixed in a liquid somehow, but it could still rotate around that point, does this mean the distance its ends would 'trace' out on a hypothetical sphere in 1 second would equal eg 40...
13. ### How can I think of rotational diffusion inverse seconds?

When thinking of a spherical shaped particle moving about under Brownian motion, one describes its motion by Diffusion. The units being \frac{m^2}{s} I can understand this physically as a distance it will travel from a certain point in space averaged over x-y and z direction. Now rotational...
14. ### Understanding derivation of scattering from Maxwells eqns

This kind of derivation is in a lot of light scattering books and I have never understood it because they never seem to go into enough detail for me. I am beginning to 'get' it now though.
15. ### Understanding derivation of scattering from Maxwells eqns

Thank you very much, that is excellent. It is details like these that books just do not say and I find them incredibly necessary for my understanding. So eqn [4] and [5] are put in as they describe how the material 'responds' to the incoming field. The one thing I still cant wrap my head around...