Astudy showed that children who watch more than five or more hours of television a day have lower grades than children who watch less. which of these could be a hidden variable?

a. tv viewing could lead to depression.
b. children who watch television might also play video games.
c. tv viewing and school grades might not be related.
d. children who watch more television may have parents who are home less often to them with schoolwork.

i think it could possibly be b

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: