1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Alternating Current (multiple CHoice)

  1. Dec 2, 2011 #1
    1. The problem statement, all variables and given/known data
    An alternating voltage is given by [tex]v = 30\sin(314t)[/tex].The time taken by the voltage to reach 30V for the first time is:
    A. 0.02s
    B. 0.03s
    C. 0.1s
    D. 0.015s

    2. Relevant equations
    google for equation for instantaneaous current and voltage

    3. The attempt at a solution
    30 = 30sin(314t)
    1 = sin(314t)
    pi/2 = 314t
    t = 0.005s
    not in the choices

    EDIT
    30 = 30sin(314t - pi)
    pi/2 = (314t - pi)
    t = 0.015 from the choices

    why do i need to subtract 180 degrees inside the sine eqn instead of adding
    ( Formula for n repeating cycles is v(t + nT) )
     
    Last edited: Dec 2, 2011
  2. jcsd
  3. Dec 2, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    It would appear that the question is incorrect. Starting from time t = 0, the first positive peak occurs at approximately 5ms (milliseconds), which is what you first calculated.

    By the way, is that the complete statement of the question in its original form?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Alternating Current (multiple CHoice)
  1. Multiple choice? (Replies: 1)

  2. Multiple Choice (Replies: 3)

Loading...