Two straight wires are in parallel and carry electric currents in opposite directions and with the same magnitude of 2.0 A. The distance between the two wires is 5.0 mm. One wire is infinitively long and the other wire is 0.30 m long. Is the magnetic force between the two wires repulsive or attractive? What is the magnitude of the magnetic force between them?

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you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m