Half of the moon is illuminated.
Here observer is moving along with an electrical charge
now magnetic field on a moving charge is given by equation

electrical force on a moving charge is given by formula

so here we can say when observer is moving with the charge it will have two forces on it
1. magnetic force due to existing magnetic field
2. electric force due to electric field
so here he must have to experience both type of field presence
So here correct answer must be
<em>C- electric and magnetic fields </em>
Police siren is the correct answer. Hope this helps.
Answer:
The essential characteristics of an object in equilibrium is acceleration of the object must be zero.
Explanation:
Equilibrium: An object acted upon by several forces is said to be in equilibrium if it does no it moves or rotate. Equilibrium can be defined as the state of stability of an object.
Condition for equilibrium
(i) The resultant force acting on the object must me equal to zero.
(ii) The sum of moment acting on the object must be equal to zero.
But.
F = ma..................... Equation 1
Where F = net force , m = mass, a = acceleration.
from the equation above,
For F = 0 N, a must be equal to zero.
<em>From the above, the essential characteristics of an object in equilibrium is acceleration must be zero</em>
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