What Are Common Mistakes in Calculating Magnetic Forces and Particle Velocities?

[supermenscher]

1. A 10.9E-6 particle with mass 2.80E-5kg moves perpendicular to a 1.01 magnetic field in a circular path of radius 26.6m. How fast is the particle moving? How long will it take the particle to complete one orbit?

I used v=rqB/m and got the wrong answer for velocity and I have no idea how to get the time.


2. A high voltage power line carries a current of 110A at a location where the Earth's magnetic field has a magnitude of 0.45E-4T and points to the north, 72 degrees below the horizontal. Find the direction and magnitude of the magnetic force exerted on a 210m length of wired if the current in the wire flows in the following directions.
a. horizontally to the east
find the force and degree and direction of the horizontal
b. horizontally toward the south
find the force and direction (north, south, east, west)

I used F=ILBsintheta
and got the incorrect answer
Can anyone show me what to do...tht would be very helpful

 

[krab]

1. Use v=rqB/m and get the right answer. Seriously. You probably are not using the physical quantities correctly. I notice you say a 10.9e-6 particle and a 1.01 magnetic field, with no dimensions. So I'm guessing you have a problem with dimensions. Physics is much more than just finding a formula and plugging numbers in. You have to know what the formulas mean.

Also, are you seriously saying that if you know the radius and speed in a circular orbit you cannot derive the orbit time? Here's an analogous situation: you travel 60 mph; how long does it take you to travel 10 miles?

 

[M98Ranger]

1. For the first problem, the equation you used is correct. However, make sure to convert all units to SI units before plugging them into the equation. In this case, the mass should be in kilograms, the magnetic field strength should be in Tesla, and the radius should be in meters. Once you have converted all units, the equation should give you the correct answer for the velocity.

To find the time it takes for the particle to complete one orbit, you can use the equation T = 2πr/v, where T is the time period, r is the radius, and v is the velocity. Again, make sure to use SI units for all values in the equation.

2. For the second problem, the equation you used is also correct. Again, make sure to use SI units for all values. To find the direction and magnitude of the magnetic force, you can use the right-hand rule. Point your thumb in the direction of the current, your fingers in the direction of the magnetic field, and the force will be perpendicular to both.

a. For the force exerted on the wire when the current is flowing horizontally to the east, the direction of the force will be upward (using the right-hand rule). To find the magnitude, plug in the values for current, length, and magnetic field strength in the equation F = ILBsinθ, where θ is the angle between the current and magnetic field (90 degrees in this case).

b. For the force exerted on the wire when the current is flowing horizontally toward the south, the direction of the force will be to the west (again, using the right-hand rule). To find the magnitude, use the same equation as above, but this time the angle θ will be 162 degrees (72 degrees below the horizontal plus 90 degrees to account for the horizontal current).

If you are still getting incorrect answers, make sure to double check your calculations and conversions. It may also be helpful to draw a diagram to visualize the problem and the direction of the force.