# Recent content by DannyPhysika

1. ### Lens maker's equation used correctly?

Homework Statement An object is placed 60 cm from a thick double convex lens, with faces of radii of curvature 20 cm and 30 cm, with thickness of 2 cm, and index of refraction is 1.5. Find the position of the image...
2. ### Difference between two wave functions?

4. a) A certain string has a linear mass density of 0.25 kg/m and is stretched with a tension of 25 N. One end is given a sinusoidal motion with frequency 5 Hz and amplitude 0.01m. At time t=0, the end has zero displacement and is moving in the positive y-direction. Find the wave speed...
3. ### Difference between two wave functions?

I just started studying this stuff but on a couple occasions my answer was a different sign than the teacher's answer key, so I used the wrong function. This is what confuses me, how to know which to use in order to get the right sign. In the question, an end of a string is given sinusoidal...
4. ### Difference between two wave functions?

Hi, I'm looking through my teacher's notes and he says that a wave function for a sinusoidal wave can be written: y = A sin (ω t – k x) or y = A sin (k x - ω t) The textbook gives it in the second form. I think that using one over the other gives the same answer but in the opposite sign. I...
5. ### Finding electric field via a given potential

Ok I am also getting 3472.8 but I'm getting positive because it's: E = -kc((x/x+L) - ln|x+L| + 1 + ln|x|) which gives -kc(-.19) which is 3472.8?
6. ### Finding electric field via a given potential

If V = kc (integral) (x)dx/(d+x) then shouldn't E = -dV/dx where dV/dx just equals (d/dx)(kc (integral) (x)dx/(d+x)) which equals (kc(x))/(d+x) so E = -(kc)(1/2) = -8.99 x 10^3 N/C ?
7. ### Finding electric field via a given potential

Yes it is a rather badly worded problem... But yes, from my discussion with other students, we placed the rod's extreme left end at the origin. I wish I could show my work but I have it on paper and this is the last thing I have not done for this 5 problem assignment. I will have to pick one...
8. ### Finding electric field via a given potential

I've just spent time with another student with this problem and we're really lost because we've got 4 different answers from different sources and not one of them are the same. We've gotten 8.99 x 10^3 N/C, -3.47 x 10^3, -1.45 x 10^4 N/C, and 4.225 x 10^4 N/C from the above poster. Can anyone...
9. ### Finding electric field via a given potential

I've done all my work on paper and I ended up with E(x) = -kc[ln(L-x) + x/(L-x) -1 -ln|x|] where x = -d where d is 1m. It's been a couple days but I plugged in my numbers and got 1.45 x 10^4 N/C. But this is a positive answer, shouldn't the electric field be to the left/negative?
10. ### Finding electric field via a given potential

If I differentiate that with respect to d, I get that E = -(-3472) N/C which means that it is positive. But shouldn't it be negative?
11. ### Finding electric field via a given potential

Homework Statement The plastic rod of the length L=1 m has a non-uniform charge density λ=cx where positive constant c =2x10^-6 [some unit]. What unit c has to have? Find the electric potential at the point on the x axis 1 m to the left from the left end of the rod. Find the electric field at...
12. ### Finding electric field via potential

I would like to know if either: -3.47 x 10^3 N/C or -1.45 x 10^4 N/C Are correct. Thank you :)
13. ### Finding electric field via potential

Homework Statement The plastic rod of the length L=1 m has a non-uniform charge density λ=cx where positive constant c =2x10^-6 [some unit]. What unit c has to have? Find the electric potential at the point on the x axis 1 m to the left from the left end of the rod. Find the electric...
14. ### Can you clarify this step (charge density and integrals).

Hi, if you have the book: Physics for Scientists and Engineers 8E, Serway Jewett On page 675 (Chapter 23), Example 23.8 there is a step taken during the integration I don't understand: How do you go from "2r dr" in the numerator to d(r^2)? If there is info or link to the property of...
15. ### For those who have this textbook.

Yeah it's actually labeled μ in the book