1. Please help!! I have one last try on this question and I get it marked off
Transcranial magnetic stimulation (TMS) is a noninvasive technique used to stimulate regions of
the human brain. A small coil is placed on the scalp, and a brief burst of current in the coil
produces a rapidly changing magnetic field inside the brain. The induced emf can be sufficient to
stimulate neuronal activity. One such device generates a magnetic field within the brain that rises
from zero to 1.7 T in 100 ms. Determine the magnitude of the induced emf within a circle of
tissue of radius 1.5 mm and that is perpendicular to the direction of the field Your response is off
by a multiple of ten. mV
Solution
induced emf = A*dB/dt
= pi*r^2*dB/dt
= pi*(1.5*10^-3)^2*(1.7 - 0)/(100*10^-3)
= 1.20*10^-4 V
= 0.120 mV
a) f = c/lamda
= 3*10^8/(633*10^-9)
= 9.74*10^14 Hz
b) Intensity, I = power/Area
= 25*10^-3/(pi*0.001^2)
= 7958 W/m^2
c) We know, Average intensity of laser beam, I = Emax^2/(2*c*mue)

2. Emax = sqrt(2*c*mue*I)
= sqrt(2*3*10^8*4*pi*10^-7*7958)
= 2450 N/c
d) Bmax = Emax/c
= 2450/(3*10^8)
= 8.17*10^-6 T
e) Radition pressure, P = I/c
= 7958/(3*10^8)
= 2.65*10^-5 Pa
Force, F = P*A
= 2.65*10^-5*pi*0.001^2
= 8.33*10^-11 N
a = F/m
= 8.33*10^-11/50
= 1.67*10^-12 m/s^2
after t = 20s,
v = u + a*t
= 0 + 1.67*10^-12*20
= 3.34*10^-11 m/s
= 0.0334 nm/s