# Magnetic Field Strength Vs. Angle of direction

1. Sep 17, 2014

### carpekd

I have a simple question... does the magnetic field angle of direction vary when you vary the field strength?

For example, say i have a magnetoresistive sensor, which, to my knowledge only detects the magnetic field angle of direction (unlike a halls, which senses field strength). I place this sensor at a short distance X from a coil. Assuming X is constant, what would the sensor detect if I varied the current in the coil? I'm assuming that the field angle doesn't change with field strength, so the sensor would output a constant reading, but I'm not sure if that is a correct assumption.

2. Sep 18, 2014

### Simon Bridge

... the magnetic field is a vector - it assigns to each point in space a magnitude and a direction.
If it is specified that the magnitude is changed then the direction does not change. That what the words mean.

In your example - changing the current in the coil changes the magnitude of the magnetic field everywhere - but the overall shape should not change, so the direction shouldn't. Detectors which register only the direction will not see any change.

It is possible to perform some action that changes both the magnitude and direction of the magnetic field at the same time. i.e. one could expand or contract the coils in the electromagnet.

3. Sep 18, 2014

### sophiecentaur

If you are referring to the field around a coil with varying current then the answer is that the field direction at any point will not change This assumes that is a linear system with all parts behaving nicely. However, when there is another field present (e.g. the Earth's field) the field at a point will be the vector sum of both fields. As the field from the coil is reduced progressively, the direction of the resultant will tend to that of the external field. This is just like when you do a mechanics calculation involving strong springs and masses - then you reduce the spring forces until the weight force becomes significant.