7. The solenoid has uniform B (along axis) of coil. Hence current along the axis produces zero force as angle is zero.
8. The Earth field is weak , therefore force on wire is small.
Another reason is that the current is also small , hence force is small. This force is small as compared to the weight.Hence we cannot observe movement.
9. The angle is 90 degrees , hence F = BIL . Using LHR the force is 90 degrees to I and 30 degrees below the horizontal.
10. i)The angle is 90 degrees, hence F= BIL . Using LHR the force is 90 degrees from B and 20 degrees below horizontal.
ii) When the current is south to north it is parallel to the Earth horizontal component.The angle between I and B is 70 degrees. Use LHR and use only the vertical B as the horizontal B is parallel to I .Force is East to West.
11. The force is action reaction pair. The magnet is lifted hence the wire has a force downwards. Use F= BIL, where the force F= mg , where m is 0.2 grams. Hence B can be found. Use LHR to find the current is force is down on the wire carrying current of 2.0 A.
12. Wire x : force up (due to Y) greater than force down (due to Z), resultant force up.
Wire Y : force down (due to X) is equal to force up (due to X ) . resultant force zero.
Wire Z: force down (due to Y) is greater than force up(due to X) , resultant force down .
Current in the same direction.
Wire X : force down (due to Y and Z), resultant down
Wire Y: force up (due to X) equal to force down (due to Z) , resultant zero.
Wrie Z: force up (due to Y and X) , resultant up.