Suppose that the resistance between the walls of a biological cell is 4.2 × 109 ω. (a) what is the current when the potential difference between the walls is 75 mv? (b) if the current is composed of na+ ions (q = +e), how many such ions flow in 0.74 s?

(a) Current will be

(b) Number of ions will be

Explanation:

We have given that resistance of the biological cell

(a) We have given potential difference of 75 mV

So

From ohm's law we know that current is given by

(b) We have given time t = 0.74 sec

We have to find the charge

We know that charge is given by Q = it, here i is current and t is time  

So charge will be

So number of ions will be

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:

force is mass*acceleration.

we have a very small mass: 11.4*0.001 kg

if we want 0.035n of force, we need an acceleration:

0.035 = 11.4*0.001*a

a = 0.035/(11.4*0.001) m/s^2