# Accelerating electrons!

1. Mar 25, 2004

### pattiecake

An electron is accelerated through 1800V from rest and then enters a uniform 2.90T magnetic field. What are the maxium and minium values of the magnetic force this charge can experience?

Ok someone help me out here...not sure of the equation. How do the formulas for a magnetic force differ between a line of current and a moving charge?

In this case I believe the formula is Fm=QVBsin(theta). The maxium & minium force will vary with the angle measure, i.e. sin(90)=max. But how does potential difference (1800V) come in to play here? Where does the value of the magnetic field (B) come from?

2. Mar 25, 2004

### outandbeyond2004

Quick response here. 1800V is just to accelerate the electron to a certain speed before it enters the magnetic field. You need to compute that speed. A line of current? You mean a wire with current flowing through it? No this is not what the problem is about. The magnetic field about the wire is not uniform when you go peripendicular to the wire anyway. Not sure I know what F m v are. Force, mass, speed? Q = electron charge and theta = angle measured from electron's velocity to the direction of the field?

3. Mar 25, 2004

### pattiecake

Yah basically I got all my equations confused...not sure which equation for a magnetic field applies to an electron here (and if there's a different equation that applies to, for example, a long straight wire with current running through...) Although I realize the problem only deals with the magnetic field surrounding this particle.

Fm=Fb=Force of magnetic field. B=magnetic field. v=velocity of the electron. Q = electron charge. And theta = angle measured from electron's velocity to the direction of the field.

Ok, now where does can I find the value for B?

4. Mar 26, 2004

### outandbeyond2004

2.90T I believe T stands for Tesla, the unit of magnetic flux density, webers per square meter. Also called magnetic field, B.

5. Mar 26, 2004

### Staff: Mentor

finding the electron speed

Use the potential difference to find the speed of the electron as it enters the magnetic field. The electron gains energy as it falls through the potential: KE = qV (where V is potential difference).