# Homework Help: Would the light bulb light up from the electromagnetic wave?

1. Dec 4, 2011

### nake9534

In the picture below

http://www.geo.mtu.edu/rs/back/spectrum/e_mag.gif

a bulb is placed on a wire parallel to the direction of the electric field. The bulb is directly on the x-axis where the two waves cross each other.

1. Would the bulb glow when the wire is parallel to the direction of the electric field?

The wire containing the bulb is now shifted up a distance on the plane of the electric field

2. Would the brightness of the bulb be greater than, less than, or equal to that of the brightness in 1?

Now imagine that the wire with the bulb is rotated 45 degrees so that it is now oriented between the electric and magnetic fields

3. Would the brightness of the bulb be greater than, less than, or equal to that of the brightness in 1?

// My Responses
//------------------------------------…
1. I think that the bulb would light up because the wire is parallel to that of the electric field and perpendicular to that of the magnetic field.

2. I think that the bulb would have the same brightness as in the first question because the orientation of the current carrying wire does not change.

3. I think that the bulb would be less bright than that in case 1 because neither field is in the optimum location to light the bulb.

A good explanation is much appreciated
Thanks

2. Dec 5, 2011

### Drakkith

Staff Emeritus

Couple of things here.

1. The diagram of the magnetic and electric fields of a photon are simply a visualization of how the fields work, a graph of the interaction of the fields. There is no "plane", the effect is in every direction. Both the magnetic and electric fields alternate from + to - and back over time in accordance with the frequency of the light.

2. A wire is MUCH MUCH MUCH bigger than a photon is. Even if there was a plane you could not align the wire.

Last edited: Dec 5, 2011
3. Dec 5, 2011

### cmb

An electric current is induced onto a conductor of comparable length to the wavelength of the propagating wave.

An electrical load would experience this current if it were connected, for example, across the gap between two such aligned conductors, or between a conductor and a 'ground'.

The field would have to be very high to induce enough current to light a light bulb, but there would be a current. This is how radio signals are received by an antenna. It's why your TV or radio antenna has to be vertical or horizontal if the transmitter is also vertical or horizontal.

4. Dec 5, 2011

### cmb

What do you think 'polarisation' is, if there is no 'plane'? How do antennas work?

5. Dec 5, 2011

### Drakkith

Staff Emeritus
Yeah, I guess you are right. I was thinking that the polarization had to do with something else, not the EM fields.
In retrospect I now remember several threads on photon polarization I've been in before. Guess I had a brain fart.

6. Dec 5, 2011