studiot

The fraction by weight of a particular constituent in a given precipitate. For example the chemical factor for Fe in Fe2O3 is 0.6994. So if we have a precipitate of 10g of ferric oxide it contains 10 x 0.6994 g of iron Good gravimetric analysis texts offer tables of chemical factors. You can also use stochiometry of the reaction to calculate the fraction yourself, if you do not know the factor. Can you work out how to do this?

I'd be interested to learn more about those graphs. Pavel. What does the temperature variation [math]\Delta T[/math] vary from? And what is is the variation in temperature of? The carbon dioxide levels are self explanatory. The dust levels are stated as ppm dust levels in what, thae atmosphere, the ocean? And ppm measured how? The correlations are interesting, however, and hopefully less distorted than the Gore efforts. Many thanks.

So did I, isn't it?

Not to contradict ajb, but to add: It should be noted that the value of something may or may not be equal to its limit, if it only has one limit.

Although I realise you are interested in testing out Maxwell, you don't need Maxwell and vector calculus to solve this one. Indeed having a physics feel for what is going on is important. With a steady direct current, the electric field situation is the same as a line of charges, viz the charge/current density never changes and the field has radial symmetry. The E (and D) field lines must be at right angles to the B (and H) field lines. As you rightly observe the B field lines form concentric circles around the line of the conductor. How would another set of concentric circles be orthogonal to these? You asked where the flaw in your reasoning lies and I pointed to the step from 3 to 4. In step 3 you correctly say that if the E field is circular then curl E is non zero.. The error is in chosing the circular diagram, not the star in the top left of your attachment. The electric field cannot form closed loops. It starts or ends on a charge or goes to infinity. The magnetic field, however cannot have ends. It can only form closed loops. You can also apply Maxwell to show the consistency of this.

Ever the too practical Scot.

Edit sorry I missed a minus sign [math]\nabla {\bf{.J}} = - \frac{{\partial \rho }}{{\partial t}}[/math]

Where have you accounted for continuity in step3 to step 4? [math]\nabla {\bf{.J}} = \frac{{\partial \rho }}{{\partial t}}[/math] Note continuity is not one of Maxwell's equations. In free space you also have the conduction current J = 0

At least show that you can correctly add two forces.

Ah magic, I should have known it was not real science. Sorry I am in the wrong forum.

Vacuum cored Tx?

Sensei and strange, sounds like you two are quibbling. This is meant to be basic and elementary to present concepts and promote understanding. What exactly did you not understand?

yahya, Did you miss post#4 or are only certain members allowed to comment?

Tylers, This is all getting very complicated. One simple distinction you should know is the difference between atoms and molecules. All atoms are molecules. But not all molecules are atoms. Molecules are the smallest unit of any substance (ie matter). The definition of any pure substance is that all the molecules are the same. Some molecules can be broken down further but the results are not the original substance but atoms. Atoms are molecules of special substances, known as elements. These cannot still be broken down further and remain as matter. All molecules are made of slightly less than 150 known elements. Some elements exist in normal conditions as multiple atoms of the same element forming molecules. Examples are oxygen and hydrogen. A combination of oxygen and hydrogen exists as the water molecule. Helium normally exists molecules comprising a single atom. Hope this helps.

I think you misunderstand the nature of centripetal force. Centripetal force is a real force that has to be applied to a body travelling in a curve, by an external agent, if we can consider that body to be a point particle. Gravity is one such external agent and the gravitational force is centripetal in nature. A point particle means that all the mass of the body can be considered to act as though it was concentrated at one point. Centripetal forces act within a body turning on an axis, but not on the body as a whole. These forces act between the individual particle or parts of the body and are usually manifest as a variation in the cohesive forces holding the body together. There is a further complication in that the centripetal force at any point in the trajectory (which may not be a circle), is directed towards the centre of a circle, which has a common tangent to the trajectory curve at the point of interest. In general, when the trajectory is not a circle, this centre point will vary in position and the distance between the common tangent point and the centre (known as the radius of curvature) will vary. In order to account for this it is usual to work in terms of acceleration, not force, and call this centre the 'instantaneous centre of acceleration'. Working in this way you can add the accelerations (vectorially) on any part of an orbiting planet to generate the true path of that particle on the planet. The accelerations are, as you say, separately due to the centripetal effect of gravity acting on the planet as a whole combined with the internal accelerations due to spin, wobble and other movements, including variation of linear speed. Very tricky indeed.

+1 for fairness and astuteness. With all due respect I would see this as a political statement rather than a scientific one.

I like levity +1, sunshaker.

How about this famous one http://en.wikipedia.org/wiki/Growth_in_a_Time_of_Debt

+1 Never seen one of these, thanks.

Again I am currently short of time but you are missing part of the equation [math]{\bf{B}} = {\mu _0}{\bf{H}} + {\mu _0}{\bf{M}} = {\mu _0}\left( {1 + \frac{M}{H}} \right){\bf{H}} = {\mu _0}\left( {1 + {\chi _m}} \right){\bf{H}}[/math] Look up susceptibility.

Swansont If the filings were free to move, sure. That's what happens when you put ferromagnetic material near a magnet — they attract. But the point of filings on paper is that there's friction and the filings won't necessarily move closer, regardless of "wanting" to. You just get alignment with the local field. It doesn't work like that, watch the movie carefully. Again I say remember it is a complicated 3D effect, which is why many teachers avoid it.

Fair question but think about a balance of competing forces. Remember also that the magnetism in the filings is induced, not permanent. I was trying to show that there is a net balance of forces on the particles from repulsion from those on either side in 2D and above/below in 3D. I meant to add these into my sketch this morning but, I am dealing with two domestic emergencies (a result of crappy electrical design) at this moment. One in the fans of my fan ovens in the cooker and the other in the mains input filter to the washing machine. Why can't modern manufacturers make things last for more than a year?

Because the nearest end of any particle to the bar magnet will be of the opposite pole! This is as I tried to show in my sketch. So the end of the first particle adjacent to the north pole of the bar will be a south pole and so on. Here is an expanded sketch of the north end of the magnet showing what I mean. Did you notice that the second video on the iron filings said that it is a three dimensional effect (which you can see if you look carefully). We are only drawing two dimensional sections through this.

This is the difficulty in comparing the field distribution in a medium that can be physically moved by the field and one that can't. If you had a small enough compass you could use the following method to see that there is next to no field between the chains of filings. https://www.youtube.com/watch?v=JUZC679CwKs Without the filings the field pervades all space and anywhere the girls starts her point you can trace a line. But usually this is not discussed when filings are used to show the shape of the plot. https://www.youtube.com/watch?v=j8XNHlV6Qxg

Not really, no, but we gloss over that for elementary demonstrations. A flat steel sheet would be closer to the air/free space distribution, although more tightly 'pulled in' to the bar magnet. The 'shape' remains the same, but the distribution of the lines changes. Remember for free space or a flat sheet the lines can't interact since the tiny magnets are fixed in space. But the use of filings allows the lines to interact, although it exhibits the same onion shape from the bar.