# Homework Help: What is the magnitude of an electric field at a certain time?

1. Apr 10, 2013

### tinabelcher_13

The figure (http://tinypic.com/r/vo5ssm/6) shows the time variation of the magnitude of the electric field of an electromagnetic wave produced by a wire antenna.

What is the magnitude of the electric field at t = 3.34 × 10−10 s?
What is the magnitude of the magnetic field at t = 6.0 × 10−9 s and at t = 6.67 × 10−10 s?

I keep looking throughout the chapter to figure some kind of equations. The only ones I see

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2. Apr 10, 2013

### cepheid

Staff Emeritus
Welcome to PF tinabelcher_13!

Why do you feel that you need equations? You have a graph of the magnitude of the E field vs. time in front of you. What's prevent you from just reading the value of the magnitude at specific times from the graph?

EDIT: Okay, so the graph doesn't have very good time resolution, but the variation is sinusoidal, with an amplitude, phase, and period that you can determine from reading the graph. Once you have that (sinusoidal equation for E vs. t) you can answer the questions. The magnitude of the B field is related to the E field by a constant.