1.(a) Magnetic force on a single wire = B.l.J
Hence, magentic force on N wires = NBlJ
(b) Torque = (NBlJ).l = NBl^2J
(c) Torque produced by the object at the axle of the motor
= mg x (6/100) = 0.06mg = 0.6m
where g is the acceleration due to gravity, taken to be 10 m/s^2
The motor stops rotating when the magnetic torque equals the torque produced by the object.
Hence, NBl^2J = 0.6m
i.e. 4 x 0.2 x (0.1)^2 x 10 = 0.6m
m = 0.133 kg
2. (a) Yes, it is correct.
(b) How is Peter's circuit? It is not described in the question.
3. In general, not all momentum of the wind is transferred to drive the wind turbine, and there is energy loss due to friction.
4. The cooling capacity per unit input power for condition X = 1600/800 = 2 watts per watt
The cooling capacity per unit input power for condition Y = 2400/1200 = 2 watts per watt
Therefore, both conditioners X and Y are having the same cooling capacity.