Recent content by physfan

If the full query can't be answered can someone please just explain why the energy gap against temperature can be approximated linearly at room temperature and higher like this http://ece-www.colorado.edu/~bart/book/book/chapter2/ch2_3.htm#tab2_3_1 but is in reality more like this...

If there's any more information I can give to help please let me know :smile:

Homework Statement [Edit: Please also see additional posts below. I have tried to clarify my question somewhat but didn't want to edit this one just incase anyone can help with the full problem. Thanks! :) ] I did a lab on the band gap in germanium where I measured the voltage across a...

Oh yeah you just divide throughout by cos theta! Right, got it, thanks again (Edit: and for the record, I did that before I saw your post...)

Sorry! My notes are rather messy and I typed out the wrong bit. I meant: F(cos theta - mu*sin theta)=mu*W so F=(mu*W)/(cos theta-mu*sin theta). which is where I got stuck but if that's right I'll have another look first. Thanks!

Yup, thought so, but I'm still not getting the right result... I used n=Fsintheta + mg earlier in post #6... which shows my latest (unsuccessful) attempt. I can't really see how to carry it on.

You mean the right result? Yes, it's definitely supposed to be 1-mu*tan theta on the bottom...

I'm from England, there's just one teacher I have who calls it the "reaction" to the plane. So if we take the direction of n to be positive, why is Fsin theta also positive... isn't that acting in the opposite direction? i.e. pushing down, therefore adding to the weight?

Right, I'm now getting: For y: F*sin theta+W - n=0 so F*sin theta+W=n For x: F*cos theta - mu*n=0 so F*cos theta = mu*n Substituting in the first equation for n: F*cos theta=mu*(F*sin theta+W) F*cos theta=mu*F*sin theta+mu*W F*(cos theta - mu*sin theta)=mu*W so...

Oh hang on, F*sin theta + W = n doesn't it... sorry, I don't know why I didn't write that before. Blonde moment... I'll have another go.

Oh and the angle theta is above the horizontal.

Yeah for R I do mean the normal force, I've heard it as both R and n depending on the teacher... I prefer n to be honest but my teacher today is an R person. Looking at y now I'm thinking F*sin theta - n = 0 (hence F*sin theta = n) but that doesn't seem to get me any further than my previous...

Homework Statement A box of weight W is pushed by a force F on a horizontal floor (the diagram below shows the force on the box is at an angle theta to the horizontal) If the coefficient of static friction is mu, show that the minimum value of F that will move the crate is given by...