# Search results

1. ### How to find the temperature of a black body?

It's online homework that i copied and pasted, it's okay though.. thank you for your time and attempting!
2. ### How to find the temperature of a black body?

Okay so i found lamba which i got .075, then divided that by b (the constant) and got 25.88 which is still wrong. :(
3. ### How to find the temperature of a black body?

Ahh * photons. And yes, this is the problem. Suppose a blackbody emits photons strongly with a frequency near 4 GHz. What is the photon energy? And then i found the value that i stated above (in J), which is correct. The question then asks for the temperature of the black body and that's...
4. ### How to find the temperature of a black body?

E=hc/lambda? So i solve for lambda and plug it into my above equation? Does v=4E+9?
5. ### How to find the temperature of a black body?

Homework Statement It emits protons with a frequency of 4 GHz, and has a photon energy of 2.65E-24 J. I tried to use the formula lambda=c/f=vT, but i am somehow getting a negative answer which doesn't make sense when trying to find temperature in (K). Any help is greatly appreciated.
6. ### Length contraction.

aha i see, thank you so much!
7. ### Length contraction.

I guess that means i am, so i switch 300 and 445?
8. ### Length contraction.

Well L1 is supposed to be the length observed by an observer in relative motion with respect to the object, which would be 445?
9. ### Length contraction.

Homework Statement A spaceship moves past you at speed v. You measure the ship to be 300 m long, whereas an astronaut on the ship measures a length of 445 m. Find v. The Attempt at a Solution I tried to substitute my numbers into L1=Lsqrt(1/(v^2/c^2)) and keep getting a negative wrong...
10. ### Frequency of Xrays

So what is the speed? Is it the constant c, 3E8? And will using that give me my answer in Hz?
11. ### Frequency of Xrays

Homework Statement X-rays are electromagnetic waves with very short wavelengths. Suppose an X-ray has an wavelength of 0.126 nm. What is its frequency? The Attempt at a Solution I tried (1)/(1.26E-10)=7936507937, which is in Hz, but they want it to GHz, so i converted it and got 7.94 GHz...
12. ### Magnetic field due to wires.

Well then i would have to use B = ul/2pir? So do i just find that for each of the wires and then add them together?
13. ### Magnetic field due to wires.

Homework Statement Because of the 2 wires in the figure, For what value of the ratio I1/I2 is the magnetic field zero at the point A? point B? point C? Homework Equations http://tinypic.com/r/5otweg/7 The Attempt at a Solution I honestly have no idea where to start with this problem, any...
14. ### Magnetic field of a solenoid.

Homework Statement A 10 cm long solenoid with 241 turns and radius R = 3.00 cm has a current flowing through it of Io = 200 mA. What is the magnetic field strength inside the solenoid (in T)? The Attempt at a Solution So i know i have to use the formula B = (uo)(n)(Io) uo = a constant 1.257...
15. ### Resistivity of a wire.

Homework Statement A wire has a diameter of 1.51 mm and a length of 32.7 m, and is found to have a resistance of 1.5 capital omega. What is the resistivity of the wire? Homework Equations The Attempt at a Solution R=qL/A R=.0051/2=7.55E-4 L=32.7 A = ? How do i find A to...
16. ### How to find current through resistors.

Homework Statement Two resistors with R1 = 1755 omega and R2 = 4020 omega are connected in parallel. The battery emf is large epsilon = 15 V. What is the current through resistors R1? What is the current through resistors R2? Homework Equations The Attempt at a Solution I...
17. ### Temperature coefficient of resistance problem

Homework Statement For the resistance versus temperature graph below, find (a) the resistance at T = 20°C and (b) the temperature coefficient of resistance alpha . http://tinypic.com/r/jhufkn/7 I don't know if the graph is showing up or not, it isn't for me... so here's the link...
18. ### How to find a charge on a sphere in equilibrium?

How do i incorporate the string in?!
19. ### How to find a charge on a sphere in equilibrium?

Homework Statement A small, plastic sphere of mass m = 126 g is attached to a string as shown in the figure. There is an electric field of 151 N/C directed along the + x axis. If the string makes an angle 30 with the y axis when the sphere is in equilibrium, what is the charge on the...

21. ### Electromagnetic forces, finding alpha.

Homework Statement When a third charge is placed at the origin, it is found that the force on it is zero. Find alpha? Two charges Q and 5Q are located as shown in the figure below. https://chip.physics.purdue.edu/protected/GiordanoEMimg/chapter17/17prob16.jpg If possible, please...