Cual es el periodo entre cresta y cresta, si una onda viaja de 85ms, si la distancia
es de 4.5m. Y cual es su frecuencia.

translation: What is the period between crest and crest, if a

wave travels 85ms, if distance

is 4.5m. And what is its frequency.

Lo siento, pero no puedo responder a tu pregunta.

(también la gente informará si lo hace en inglés mentalmente en un idioma diferente, así que ... tal vez traducir)

it becomes positively charged by charging it

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.