Around flat metal coil has 180 turns and negligible resistance. it is connected in a series circuit with a 17-ω resistor, with nothing else in the circuit. you measure that a 6.0-a current flows through the resistor when a magnetic field through the coil, perpendicular to its area, is changing at 3.0 t/s. what is the radius of the coil?

(a) 0.043 m
(b) 0.014 m
(c) 0.25 m
(d) 0.54 m

C) 0.25 m

Explanation: In order to explain this problem we have to consider the Faraday law, we have:

ε=-dФ/dt where ε the emf induced by the change of the magnetic field given by dФ/dt.

then ε=I*R=17*6=102 V

We have a coil then we have the magnetic flux as follow:

Ф=N*A*B then we have

dФ/dt= N*A*dB/dt  where A and N is the area and number of turn of the coil.

A=π*R^2 where R is the radius of teh coil.

Finally we have;

dФ/dt= N*π*R^2*dB/dt then

R= [dФ/dt/(N*π*dB/dt)]^1/2= [102/(180*π*3)]1/2=245.2*10^-3=≅0.25m

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.