Please answer ALL questions to receive a rating, thanks! 1.) A 13.3 F capacitor

Question

Please answer ALL questions to receive a rating, thanks!

1.) A 13.3 F capacitor is charged to a potential of 45.0 V and then discharged through an 80.0 resistor.

(a) How long after discharge begins does it take for the capacitor to lose 90.0% of the following?

(i) its initial charge
(No Response) s

(ii) its initial energy
(No Response) s

(b) What is the current through the resistor at both times in part (a)?

(i) at tcharge
(No Response) A

(ii) at tenergy
(No Response) A

2.)A single ion channel is selectively permeable to K+ and has a resistance of 1.0 G. During an experiment the channel is open for approximately 1.0 ms while the voltage across the channel is maintained at +68 mV with a patch clamp. How many K+ ions travel through the channel?
(No Response) ions

3.)A long, straight wire carries current in the +x direction. Determine the direction of the magnetic field due to the current at the points O, P, Q, and R (see figure below).

Direction of the magnetic field at O:

a) +z

b) z    

c) +y

d) y

Direction of the magnetic field at P:

a) +z

b) z    

c) +y

d) y

Direction of the magnetic field at Q:

a) +z

b) z    

c) +y

d) y

Direction of the magnetic field at R:

a) +z

b) z    

c) +y

d) y

Explanation / Answer

1.
a) i)Q/ Qo = e ^ [-t/ (RC)]
   0.9 =  e ^ [-t/ (13.3*80e-6]
   0.9 = e ^ (-939.85 t)
t = 0.112ms
ii) Initial Energy stored = 0.5 * Qo²/ C
Final energy stored = 0.9 {0.5 * Qo²/ C) = 0.5 Q ²/C

0.9 Qo² = Q ²
Q/ Qo = 0.949 = e ^ (-939.85 t)

t =0.056 ms

b)i) i = v/R = 4.5/80 = 0.056 Amps.

2) Use I = V/R to find the current.

Use Q = It to find the charge, Q, that flows.

Since the charge on a K+ ion is 1.6x10¹C, divide Q by 1.6x10¹C and this is the number of K+ ions.

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