What must be true of the direction of the current in the electromagnets of a dc motor? it needs to be perpendicular. it needs to be parallel. it needs to be switched repeatedly. it needs to stay the same.

Acylindrical specimen of a nickel alloy having an elastic modulus of 207 gpa (30 × 106psi) and an original diameter of 10.2 mm (0.40 in.) experiences only elastic deformation when a tensile load of 8900 n (2000 lbf) is applied. compute the maximum length of the specimen before deformation if the maximum allowable elongation is 0.25 mm (0.010 in.)

Imagine that someone pushes one marble toward a motionless marble. would there still be action-reaction forces involved in the collision? how might the marbles’ motions be changed? ?

Find the magnetic field a distance r from the center of a long wire that has radius a and carries a uniform current per unit area j in the positive z direction.