Answer:

Explanation:
As we know that the magnetic field near the center of solenoid is given as

now we know that initially the length of the solenoid is L = 18 cm and N number of turns are wounded on it
So the magnetic field at the center of the solenoid is 2 mT
now we pulled the coils apart and the length of solenoid is increased as L = 21 cm
so we have

now plug in all values in it


Answer:
The ratio is 1:1
Explanation:
Firstly we are told the in (a) we have a force which A given to be: FA
We are then told the are two other forces which a B and C which are equal.
These forces are given to be F and 19.5° away from A.
We are then told that the force on the elephant is now three times, of what it was when we only had force A.
Since we are told that B and C are eqaula.
If we say FA = 2N
Then in order for it to be three times, we would have to add 4N since it was the only force present at the time.
If we add two equal forces, then we can devide that 4 by 2.
We then find out that F =2N
and thus equal to FA.
Therefore the ratio of F/FA is
!:1
True because they will work good with eachother