Question 7 of 10 Why are railroad tracks built with a flexible expansion and contraction joint? A. The two have equal coefficients of linear expansion. O B. The tracks have a smaller coefficient of linear expansion than the ground beneath. O C. The ground beneath has a larger coefficient of linear expansion than the tracks. O D. The tracks have a larger coefficient of linear expansion than the ground beneath.​

Currents in dc transmission lines can be 100 a or higher. some people are concerned that the electromagnetic fields from such lines near their homes could pose health dangers. for a line that has current 150 a and a height of 8.0 m above the ground, what magnetic field does the line produce at ground level? express your answer in teslas and as a percentage of the earth’s magnetic field, which is 0.50 g. is this value cause for worry?