Answer:
D. 130 J
Explanation:
The coefficient of performance for a machine that is being used to cool, is given by:
Here 
is the heat removed from the cold reservoir, W is the work required, that is, the energy required to remove the heat from the interior of the house, 
is the cold temperature and 
is the hot temperature. Recall use absolutes temperatures(
). Replacing and solving for W:
Electromagnets can be turned off, this makes it easier to release things from the magnetic field.
Hope this helps :)
Answer: 10.58 C has flowed during the lightning bolt
Explanation:
Given that;
Time of flow t = 1.2 × 10⁻³
perpendicular distance r = 21 m
Magnetic field B = 8.4 x 10⁻⁵ T
Now lets consider the expression for magnetic field;
B = u₀I / 2πr
the current flow is;
I = ( B × 2πr ) / u₀
so we substitute
I = ( (8.4 x 10⁻⁵) × 2 × 3.14 × 21 ) / 4π ×10⁻⁷
= 0.01107792 / 0.000001256
= 8820 A
Hence the charge flows during lightning bolt will be;
q = It
so we substitute
q = 8820 × 1.2 × 10⁻³
q = 10.58 C
therefore 10.58 C has flowed during the lightning bolt
