# Homework Help: Questions about signalsPlz help me

1. Jan 4, 2006

### dervast

a)Hi i want to know what do we mean that 2 signals are in phase, For example in an electromagnetic signal the E and B vectors are always in the same phase right?

b)Also i am trying to find information about pounting vector.. It seems that the pounting vector denotes the flux of energy.... Can u explain it more to me?

2. Jan 4, 2006

### chroot

Staff Emeritus

When two quantities are "in phase," their crests are coincident, as are their troughs. Note on the linked page the equations:

Since the arguments of the sine function are the same, both fields have their maxima and minima at the same time, and are thus in phase.

Further down on the same page, you'll see the definition of the Poynting vector:

The Poynting vector represents the flux of energy per unit area.

- Warren

Last edited: Jan 4, 2006
3. Jan 5, 2006

### dervast

Thx a lot for your answers... I have aksed u about the Punting vector because we use it in a wireless lesoon.. I have written the links u gave me but for being honest i can still figure out (graphical representation cant be created) how the pounting vector is... Thx a lot Have a happy new year

4. Jan 5, 2006

### dervast

Thx a lot for your answers... I have aksed u about the Punting vector because we use it in a wireless lesoon.. I have written the links u gave me but for being honest i can still figure out (graphical representation cant be created) how the pounting vector is... Thx a lot Have a happy new year

5. Jan 5, 2006

### chroot

Staff Emeritus
The electric and magnetic fields are at right angle to each other; the Poynting vector is at right angles to both.

If the electic field has oscillations in the x direction, and the magnetic field has oscillations in the y direction, then the Poynting vector is in the z direction.

The Poynting vector is in the direction in which the signal travels; the electric and magnetic fields are perpendicular to it.

- Warren

6. Jan 7, 2006

### dervast

Thx and something more...why physicians have created the term pounting vector. E and B components of an Electromagnetic signal werent enough for that?

7. Jan 7, 2006

### chroot

Staff Emeritus
1) They're called physicists, not physicians.
2) The vector is useful, because it points in the direction of the movement of energy.
3) Most things that are useful in math or physics are given names, so that communication between mathematicians or physicists can be made more efficient.

- Warren