What force cause the rod to become charged

When a polythene rod is rubbed with a duster, the friction causes electrons to gain energy. Electrons gain enough energy to leave the atom and 'rub off' onto the polythene rod. The polythene rod has gained electrons, giving it a negative charge. The duster has lost electrons, giving it a positive charge.

electricity

If a rod is charged it is because of the electrical force acting on it

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: