A.
Destructive interference is when two waves cancel each other out or when the crest of one wave passes through the trough of another wave.
Before 7 after 9. A pH smaller than 7 indicates acidity with 0 being completely acidic. A pH greater than 7 shows alkalinity with 14 being completely alkaline. 7 is neutral. Since NaOH is alkaline, adding it to a neutral substance would increase the pH and it would increase from 7 to 9.
Explanation:
Given that,
Charge 1, 
Charge 2, 
The distance between charges, r = 1.99 m
To find,
The electrostatic force and its nature
Solution,
(a) The electric force between two charges is given by :



(b) As the magnitude of both charges is positive, then the force between charges will be repulsive.
Therefore, this is the required solution.
Answer:
No
Explanation:
The lines of the field of a magnet don't begin or stop at anyplace, they generally make shut circles or loops and will proceed inside magnet (however here and there they are not drawn along these lines). We require an approach to show the bearing of the field.
The field lines of a magnet don't simply end at the magnetic tip. They go directly through it, so that inside the magnet the magnetic field lines indicates from the south to the north pole.