15. Electromagnetism

Content

• Force on a current-carrying conductor

• Force on a moving charge

• Magnetic fields due to currents

• Force between current-carrying conductors

Learning Outcomes

Candidates should be able to:

(e) predict the direction of the force on a charge moving in a magnetic field.

(f) recall and solve problems using F = v.B.q.sin?.

(g) describe and analyze deflections of beams of charged particles by uniform electric and uniform magnetic fields.

(h) explain how electric and magnetic fields can be used in velocity selection for charged particles.

assume vyo = 0 m/s, vzo = 0 m/s

E

explore when vxo = 0 m/s

1 the simulation can be used to explore F_B force on beam of charged particles q in a magnetic field B.

2 set the vxo = 0 m/s, Bx = 1 T, By = 0 T, Bz = 0 T, click on the run button to start the simulation.

3 record the path (trail left behind the particles motion) of the charged particle q.

hint: it is stationary? record it

4 try other values of Bx, then follow by By, then follow by Bz.

hint: it is stationary? record it

what can be concluded about the relationship of v to F_B ?

E1 explore when vxo = 1 m/s

1 set the vxo = 1 m/s, Bx = 1 T, By = 0 T, Bz = 0 T , (optional) click on the run button to start the simulation.

2 record the direction of F_B (view the applet, as well as the column F_Bx, F_By and F_Bz to make sense)

3 try other values of Bx, then follow by By, then follow by Bz.

4 record your data systematically in a table

E2 explore when vxo = -1 m/s

1 set the vxo = -1 m/s, Bx = 1 T, By = 0 T, Bz = 0 T , (optional) click on the run button to start the simulation.

2 record the direction of F_B (view the applet, as well as the column F_Bx, F_By and F_Bz to make sense)

3 try other values of Bx, then follow by By, then follow by Bz.

4 record your data systematically in a table

E3 to scaffold the learning, verify this hypothesis that claims

F_B = v^B*q for advanced learners

or

using left hand rule, F_B (thumb) B (index finger) and i (middle finger) in 90 degree angle to each other, can be used to predict the direction of the F_B. for normal learners.

hint: direction of +i is the same as +q, because i = d(N.q)/dt

discuss with your classmates to verify this relationship.

E4 Extend this hypothesis to vxo = 0 m/s, vyo = 1 m/s, vzo = 0 m/s

vary the values of Bx = 1 T, By = 0 T, Bz = 0 T

Bx = 0 T, By = 1 T, Bz = 0 T

Bx = 0 T, By = 0 T, Bz = 1 T

can F_B = v^B*q or left hand rule, F_B (thumb) B (index finger) and i (middle finger) still predict the direction of the force?

record down the data your observed

E5 Extend this hypothesis to vxo = 0 m/s, vyo = 0 m/s, vzo = 1 m/s

vary the values of Bx = 1 T, By = 0 T, Bz = 0 T

Bx = 0 T, By = 1 T, Bz = 0 T

Bx = 0 T, By = 0 T, Bz = 1 T

can F_B = v^B*q or left hand rule, F_B (thumb) B (index finger) and i (middle finger) still predict the direction of the force?

record down the data your observed

E6 q is negative

with reference to activity E1, explore when vxo = 1 m/s

1 set the vxo = 1 m/s, Bx = 1 T, By = 0 T, Bz = 0 T , (optional) click on the run button to start the simulation.

1.5 change q to -1 C

2 record the direction of F_B (view the applet, as well as the column F_Bx, F_By and F_Bz to make sense)

3 try other values of Bx, then follow by By, then follow by Bz.

4 record your data systematically in a table

what can be concluded about the effect of q on the direction of F_B ?

how does the left hand rule stand up to this new data?

discuss how to rationalize this especially with respect to i = d(N.q)/dt

discuss with your classmates to make sense of this new data on the relationship: left hand rule, F_B (thumb) B (index finger) and i (middle finger).