How can you be certain that a chemical change has occurred? a) there is at least one substance that was not present before the change b) the amount of measurable material is different after the change c) the change substance have become warmer d) at least one substance undergoes a change of state

The magnitude of the magnetic field at a certain distance from a long, straight conductor is represented by b. what is the magnitude of the magnetic field at twice the distance from the conductor? a. at twice the distance, the magnitude of the field is 4b. b. at twice the distance, the magnitude of the field is 2b. c. at twice the distance, the magnitude of the field is b/2.d. at twice the distance, the magnitude of the field is b/4.e. at twice the distance, the magnitude of the field remains equal to b.