A2.1 m long straight horizontal wire carrying a current of 5.1 a along the +x-direction is in a region of uniform magnetic field, b. if the mass of this wire is 0.2 kg, find the magnitude and direction of the magnetic field necessary to have this wire "float" in the earth's gravitational field. (assume the force due to gravity is in the −y-direction.)

It is really hard for me right know

The experiment done in lab is repeated, using a ball that has unknown mass m. you plot your data in the form of f 2 versus m/l, with f in rev/s, m in kg, and l in m. your data falls close to a straight line that has slope 3.19 m/(kg · s2). use g = 9.80 m/s2 and calculate the mass m of the ball.

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?