What must happen for a electromagnet to have a magnetic field

Four identical lab carts each have a mass of 200 kg. different masses are added to the carts and the velocities are measured. all carts move to the right.

1. what is the si unit of emf? 2.a complete series circuit consists of a 12.0 v battery, a 4.70 ω resistor, and a switch in the closed position. the internal resistance of the battery is 0.30 ω. what does an ideal voltmeter read when placed across the resistor?

The goal of this experiment was to answer the question, "how does diffraction occur? " suppose you formulated this alternate hypothesis: if the gap width is increased while keeping wavelength constant, then the observed diffraction will decrease because the less the ratio between wavelength and gap width is, the smaller the observed diffraction angle will be.to test this hypothesis, you would change the  gap widthdiffraction anglewavelength  and observe the  gap widthdiffraction anglewavelength  in the system.therefore, the independent variable would be the  gap widthdiffraction anglewavelength  and the dependent variable would be the  gap widthdiffraction anglewavelength.