Consider the following. (a) Red blood cells often become charged and can be trea
ID: 2003013 • Letter: C
Question
Consider the following.
(a) Red blood cells often become charged and can be treated as point charges. Healthy red blood cells are negatively charged, but unhealthy cells (due to the presence of a bacteria, for example) can become positively charged. In the figure, three red blood cells are oriented such that they are located on the corners of an equilateral triangle. The red blood cell charges are A = 2.30 pC, B = 7.50 pC, and C = 4.20 pC. Given these charges, what would the magnitude and direction of the electric field be at cell A? (1 pC = 1 1012C.)
magnitude:
=____ N/C
direction:
=____ ° counterclockwise from the +x-axis
(b) If the charge of cell A were doubled, how would the electric field at cell A change?
A) The magnitude of the field would be doubled.
B) The magnitude of the field would be quadrupled.
C) The field would be unchanged.
D) The magnitude of the field would be halved.
magnitude:
=____ N/C
direction:
Explanation / Answer
a) Using E = kq/r^2
Then the E field due to B = EBx = -(9*10^9*7.5*10^-12)/(0.0005)^2*cos60= -135000 N/C
EBy = -(9*10^9*7.5*10^-12)/(0.0005)^2*sin60 = -233826.86 N/C
The E field due to C = ECx = (9*10^9*4.2*10^-12)/(0.0005)^2 = 151200 N/C
ECy = 0
Adding these, the net E field is
Ex = 16200 N/C
Ey = -233826.86 N/C
Using polar transformation,
Magntitude: 234387.37 = 2.34*10^5 N/C
Direction: 273.96 degrees
b) The E field is independent of the charge feeling the field. Thus, IT WILL BE UNCHANGED. (option C)