Answer:
she must increase the current by factor of 7
Explanation:
The magnetic field produced by a steady current flowing in a very long straight wire encircles the wire.In order to solve the question, we use this formula,
B= μo I/(2πr)
where,
'μo' represents permeability of free space i.e 4π*10-7 N/A2
B=magnetic field
I= current
r=radius
->When r= 1cm=> 0.01m
B1 = μo /(2π x 0.01)
->when r=7cm =>0.07m
B2 = μo /(2π x 0.07)
Now equating both of the magnetic fields, we have
B1= B2
μo /(2π x 0.01)= μo
/(2π x 0.07)
/
= 0.01/0.07
/
= 1/ 7
Therefore, she must increase the current by factor of 7