Answer:The magnetic field around an electromagnet is just the same as the one around a bar magnet. It can, however, be reversed by turning the battery around. Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off just by closing or opening the switch.
Answer:
convergent
Explanation:
Convergent limits are the type of boundary defined by the movement of the plates in the direction of approach, that is, when two tectonic plates move in a convergent direction, colliding between them frontally. In these cases, the dense plate dips under the lightest one, being incorporated into the warm material and fluid of the mantle.
A tsunami can be generated when the boundaries of converging tectonic plates move. For this reason, we can conclude that the type of board boundary that is close to the area that Marina has been studying is a convergent limite.
Answer: t = 0.492τ
Explanation: In a circuit where there is a resistor and a capacitor, the equation for a charging capacitor is given by:

where:
is the equilibrium charge
q is the charge at time t
RC is time constant also called τ (tau)
For this problem, the circuit is charged to 39%, which means: q = 

0.39 = 1 - 
= 0.61
= ln(0.61)
-t = ln(0.61)τ
t = 0.492τ
For the condition to be met it is needed 0.492 time constants must elapse.