Answer:
The magnitude of the magneticfield B[T] at a point on the surface of the earth directly below the power line is B=1.496x10^(-6) T.
Explanation:
The distance from the wire to a point in the surface is the heigth of the wire.
The formula for the magnetic field on any point at distance R from a wire conducting alternating current is:

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Answer:
b . force that are unequal in size but in same direction.
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Answer:
25N
Explanation:
Given parameters:
Potential energy expended = 500J
Height = 20m
Unknown:
The force used = ?
Solution:
To solve this problem, we use the expression below:
Potential energy = Force applied x height
500 = Force applied x 20
Force applied = 25N
The required increase in temperature is: 
Explanation:
When the temperature increases, the area of an object increases according to the equation

where
is the initial area
is the coefficient of linear expansion
is the change in area
is the change in temperature
For the steel ball in this problem, we have:
, so the radius is

Therefore, the surface area is

The coefficient of linear expansion for steel is

And the change in area of the ball is

Therefore, the required increase in temperature is:

Learn more about temperature:
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