Pushing wires with magnetism

Science · Forces & Motion · ages 16-18

Name ______________________ Date ____________

The left hand rule gives the force direction from field and current.
Circle one: True False
In F equals BIL sin theta, when is F largest?
- Wire at 90 degrees to the field
- Wire parallel to the field
- Wire outside the field
What is one tesla?
- One joule per coulomb
- One newton per amp metre
- One volt per metre
What force does a 5 cm, 20 A wire feel in a 1.5 T field at right angles?
- 1.5 N
- 0.15 N
- 15 N
A 0.5 m wire carries 3 A at right angles in a 2 T field. F equals BIL. Give F in newtons.
Answer: ______________
A pupil uses electron flow in the left hand rule. What happens?
- The size doubles
- Nothing changes
- The predicted direction flips
A pupil says a tesla is one newton per coulomb. What is wrong?
- Tesla has no definition from force
- The pupil is right for wires
- Teslas divide by current too: one newton per amp metre
A 2 m wire carries 4 A at 30 degrees to a 3 T field. Sin 30 is 0.5. Give F in newtons.
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

True · Point fingers with field and current, and the thumb gives force.
Wire at 90 degrees to the field · Sin 90 is one, the biggest value it can take.
One newton per amp metre · The tesla is read straight from F equals BIL.
1.5 N · 20 times 0.05 times 1.5 gives 1.5 N.
3 · Multiply 2 by 3 by 0.5 to get 3 N.
The predicted direction flips · Electron flow runs opposite, so the thumb points the wrong way.
Teslas divide by current too: one newton per amp metre · Per coulomb misses the current; per amp metre is the tesla.
12 · Multiply 3 by 2 by 4 by 0.5 to get 12 N.