-- There is no need to develop the pictures. They are available immediately in a digital camera.
-- There is no change in the teacher from one picture to the next.
-- The distance the watermelon falls from the teacher in each new picture is more in each picture than in the picture before it. (C)
B represents the direction of the magnetic field around the wire
Explanation:
A wire carrying an electric current always produces a magnetic field around itself. The lines of the magnetic field produced by a current-carrying wires are concentric circles around the wire. The magnitude of the field is given by the formula:
where
is the vacuum permeability
I is the current in the wire
r is the distance from the wire
The direction of the field lines is given by the so-called right hand rule, shown in the figure. Basically, the thumb of the right hand is placed in the direction of the electric current, while the other fingers are "wrapped" around the thumb: the direction of the other fingers give the direction of the magnetic field lines.
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B.absorb neutrons to prevent chain reactions which become uncontrollable