# Thread: Circular Motion in B field

1. ## Circular Motion in B field

Again, thanks in advance for the help!

We have two charged particles of equal mass travelling along circular orbits in a region of uniform, constant magnetic field. Particle 1 has a radius of orbit r1 = 5 cm and a speed of v1=10^5 m/s. Particle 2 has Q2=2*Q1, and KE2=2*KE1.

What is the radius of orbit for R2?

I think in this situation r1=sqrt(2)r2

r2=sqrt(KE1*m1)/q1B
r1=sqrt(2*KE1*m1)/q1B

2. Originally Posted by profound
Again, thanks in advance for the help!

We have two charged particles of equal mass traveling along circular orbits in a region of uniform, constant magnetic field. Particle 1 has a radius of orbit r1 = 5 cm and a speed of v1=10^5 m/s. Particle 2 has Q2=2*Q1, and KE2=2*KE1.

What is the radius of orbit for R2?

I think in this situation r1=sqrt(2)r2

r2=sqrt(KE1*m1)/q1B
r1=sqrt(2*KE1*m1)/q1B
The centripetal force on each particle is provided by the magnetic force.

Centripetal force is proportional to velocity squared and inversely proportional to the radius. Velocity squared is proportional to K.E.

Therefore: The radius is directly proportional to K.E. and inversely proportional to the magnetic force.

Meanwhile, the magnetic force is directly proportional to both charge and velocity.