If the half life of an isotope is 20 years, how much of the original amount will remain after 20 years has passed?

If the half life of an isotope is 20 years, then half of the original amount will  remain after 20 years has passed.

That's what "half-life" means.

Similarly, after ANOTHER 20 years, 1\4 of the original amount remains.

And after ANOTHER 20 years, 1\8 of the original amount remains.

And after ANOTHER 20 years, 1\16 of the original amount remains.

And after ANOTHER 20 years, 1\32 of the original amount remains.

And after ANOTHER 20 years, 1\64 of the original amount remains.

And after ANOTHER 20 years, 1\128 of the original amount remains.

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.