Download Magnetic Field On

Magnetic Field – Charge and Current Interaction
Charge Interactions
Name: _______________
The force exerted on a charge in an electric field is given by: F = qE.
What is the equation for the force exerted on a charge in a magnetic field?

Case 1 - The charge is stationary in the magnetic field. What can you conclude?

Case 2 - The charge is moving parallel to the field. What can you conclude?

Case 3 - Three objects of equal mass, one neutral, one negative, and one positive, are all initially
moving with the same velocity perpendicular to the field, which is directed out of the screen. What
can you conclude?

Case 4 - The same as case 3 except the magnitude of the magnetic field is doubled. What can you
conclude?

Case 5 - Three positive charges +q, +2q, and +3q are initially moving perpendicular to the field with
the same velocity. What can you conclude?

Case 6 - Here we have equal charges initially moving perpendicular to the field. The initial velocities
are v, 2v, and 3v, respectively. Describe the path differences.
The charges follow circular paths at constant speed. We can apply uniform circular motion ideas: F = mv2/r .
This gives r = mv2/F
Note that we observe that r is proportional to v.
Possible paths of a charge in a uniform magnetic field
If the velocity of a charge is parallel to the magnetic field the charge moves with constant velocity because
there's no net force. If the velocity of a charge is perpendicular to the magnetic field the path is circular
because the force is always perpendicular to the velocity.
What happens when the velocity is not one of these special cases, but has a component parallel to the field
and a component perpendicular to the field?
Charge Directions in Magnetic and Electric Fields
You may indicate the correct direction next to the case question. Use the symbols for # 5 and #6.
1.
2.
3.
4.
5.
6.
7.
8.
9.
up
down
left
right
into the screen
out of the screen
a combination of two of the above
the force is zero
this case is ambiguous - we can't say for certain
Case 1: In what direction is the force on a positive charge with a velocity to the left in a uniform magnetic
field directed down and to the left?
Case 2: In what direction is the force on a negative charge with a velocity down in a uniform magnetic field
directed out of the screen?
Case 3: In what direction is the force on a positive charge that is initially stationary in a uniform magnetic
field directed into the screen?
Case 4: In what direction is the force on a negative charge with a velocity to the left in a uniform electric
field directed out of the screen?
Case 5: In what direction is the velocity of a positive charge if it feels a force directed into the screen in a
magnetic field directed right?
Rank the Charges
Three charged objects with the same mass and the same magnitude charge have initial velocities directed
right. They enter a region of uniform magnetic field from the left. You can see the trails they follow as the
move through the field. Rank the objects based on their speeds.
1.
2.
3.
4.
5.
1>2>3
2>1>3
3>2>1
3>1>2
None of the above
Rank the objects based on the magnitude of the force they experience as they travel through the magnetic
field.
1.
2.
3.
4.
1>2>3
2>1>3
3>2>1
3>1>2
5. None of the above