electromagnetism~urgent!!!!!

21(a) There is a magnetic force acting upward on the wire. By action and reaction law, a downward force acts on the magnet, thus increases its weight.

(b) The current flows out of the paper..

(c) (0.15384 - 0.15354)g = B.(0.05).(2)
where g is the acceleration due to gravity, taken to be 10 m/s^2
B is the magnetic flux density
Hence, 0.003 = B(0.05).(2)
B = 0.03 T

(c) From (c), magnetic force = 0.003 N
Hence, new balance reading = (0.15354 - 0.003/g) kg = 0.15324 kg = 153.24 g

22.(a) Since the reading on the balance decreases, it shows that there is an upward magnetic force acting on the section of wire BC.

By Fleming's Left Hand Rule (Motor Rule), the magnetic field lines are pointing into the paper.

(b) There is an upward magnetic force acting on the section BC, this upward force reduces the weight of the loop, causing the reduction of the balance reading.

(c) Magnetic force = (0.050044 - 0.050021)g N = 2.3 x 10^-4 N
[ Take g, the acceleration due to gravity, to be 10 m/s^2]

Hence, 2.3x10^-4 = 0.5 x 0.15 x I where I is the current in the loop
i.e. I = 3.067 x 10^-3 A

(d) New balance reading = (0.050044 + 2.3x10^-5) kg = 0.050067 kg = 50.067 g