Delicate measurements indicate that the Earth has an electric field surrounding it, similar to that around a positively charged sphere. Its magnitude at the surface of the Earth is about 100 N/C. What charge would an oil drop of mass 2.0 x 10 15 kg have to have, in order to remain suspended by the Earth’s electric field? Give your answer in Coulombs ?

q = 1.96 10⁴ C

Explanation:

The elective force is given by

          = q E

Where E is the electric field and q the charge.

Let's use Newton's law of equilibrium for the case of the suspended drop

               F_{e} –W = 0

               F_{e} = W

               q E = m g

               q = m g / E

Let's calculate

              q = 2.0 10⁵ 9.8 / 100

              q = 1.96 10⁴ C

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:

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.