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    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.
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    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...
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    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...
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    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 The Attempt at a Solution I honestly have no idea where to start with this problem, any...
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    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...
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    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...
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    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...
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    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 . I don't know if the graph is showing up or not, it isn't for me... so here's the link...
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    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...
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    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. If possible, please...