# Homework Help: Magnetic Forces on Conductors and charges- the motor principle

1. Jan 12, 2012

### Hmpca

Magnetic Forces on Conductors and charges-- the motor principle

An electron moving through an electric field of 475 V/m and a magnetic field of 0.1T experiences no force. if the electron's direction and the directions of the electric and magnetic fields are all mutually perpendicular, what is the speed of the electron??

the given variables are mass,charge,magnetic field,and electric field,and when also know that they are all perpendicular to each other (90 degrees).

2. Jan 12, 2012

Re: Magnetic Forces on Conductors and charges-- the motor principle

If the electron is experiencing no force, you want the force of the Electric and magnetic fields to cancel.
What are the formulas for the force of electric and magnetic fields?

3. Jan 12, 2012

### Hmpca

Re: Magnetic Forces on Conductors and charges-- the motor principle

i don`t want the fields to cancel each other out. i want the speed of the electron when both fields are perpendicular( right angle to each other)
magnetic field force=qvBsineθ
electric field force=kqq over r squared.

4. Jan 12, 2012

Re: Magnetic Forces on Conductors and charges-- the motor principle

The question says the electron experiences no force, this means the force of the electric field and the force of the magnetic field cancel each other out.

The force experienced by the electron whilst in the electric field is $F = qE$
The force experienced by the electron from the magnetic field is $F = qvB$

5. Jan 12, 2012

### Hmpca

Re: Magnetic Forces on Conductors and charges-- the motor principle

so are you saying i should first figure out the electric field and then multiply it by -1 to get the value of magnetic field. when you have that rearrange the magnetic force equation for v

6. Jan 12, 2012

Re: Magnetic Forces on Conductors and charges-- the motor principle

No, you know the strength of the electric field, 475 V/m and you know the strength of the magnetic field 0.1T. For the Force to be zero the force from these 2 fields on this electron must be the same strength, opposite direction, for them to cancel.

7. Jan 12, 2012

### Hmpca

Re: Magnetic Forces on Conductors and charges-- the motor principle

yeah i got it !!!:!!)
you know what I thought... they wanted me to make the fields perpendicular to each other and THEN figure out the velocity of the electron.

8. Jan 12, 2012