Question

what should be the time period of a wave with a frequency of 250 Hz

Answer 1

time = 1 / frequency 
time = 1 /250 
time = 0.004 sec 

Answer 2

Hi !

Time period = T

Frequency = ν = 250 Hz

ν = 1/T

T = 1/ν
   = 1/250
   = 0.004 sec