Magnetic force on moving charges, and how motors work

Answer Key - Grade 11 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A wire carries 3 A across a 0.5 T magnetic field, with 0.1 m of it in the field. What force acts on it, Ari?

   0.15 N
2. 2.

   A wire carries 4 A across a 0.2 T magnetic field, with 0.3 m of it in the field. What force acts on it, Bo?

   0.24 N
3. 3.

   A wire carries 1.5 A across a 0.8 T magnetic field, with 0.4 m of it in the field. What force acts on it, Esme?

   0.48 N

4. Read this first

   Field-line diagram (example data)

   a wire sits between a magnet's north pole on the left and south pole on the right, so the field points to the right. The current in the wire flows out of the page, and a force arrow on the wire points up.

5. 4.

   In the diagram, which way does the force on the wire point, Jun?

   • To the right, along the field
   • Up
   • Out of the page
6. 5.

   In the diagram, both the current and the magnet are reversed. Which way is the force, Luz?

   • Down
   • There is no force
   • Still up
7. 6.

   In a simple motor, why does the coil turn, Milo?

   • Its two sides are pushed opposite ways
   • Both sides are pushed the same way
   • The magnet spins it by hand
8. 7.

   What does the split-ring commutator in a simple motor do, Noah?

   • Flips the current each half turn
   • Stores the battery's charge
   • Makes the magnet stronger
9. 8.

   What do the brushes in a simple motor do, Pia?

   • Clean dust off the magnet
   • Carry current to the coil
   • Slow the coil down
10. 9.

    Why does a running motor get warm, Tala?

    • Magnets give off heat
    • The commutator makes new energy
    • Some energy becomes heat
11. 10.

    If the shaft of a small motor is spun by hand, what can the motor do, Zee?

    • Nothing, since it needs a battery
    • Make a small current, like a generator
    • Turn into a magnet