1.) Bob has an old injury in his knee. Every time it rains, Bob's knee starts to hurt. One day, while sitting inside, Bob starts complaining that his knee hurts.
Obviously, that means it must be raining outside.

not necessarily. this is probably a psychological reaction to the rain.

Explanation:

Bob's knee hurts because Bob's wife hit him on the knee, because Bob complains about his knee instead of doing household chores.

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

b is the answer