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 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
2. 2.

   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

3. 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.

4. 3.

   In the diagram, the current is reversed to flow into the page. Which way is the force now, Kira?

   • Still up
   • To the left
   • Down
5. 4.

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

   • Still up
   • Down
   • There is no force
6. 5.

   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
7. 6.

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

   • Stores the battery's charge
   • Makes the magnet stronger
   • Flips the current each half turn
8. 7.

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

   • Clean dust off the magnet
   • Slow the coil down
   • Carry current to the coil
9. 8.

   What energy change does an electric motor make, Ren?

   • Kinetic to electrical
   • Electrical to kinetic
   • Light to electrical
10. 9.

    Why does a running motor get warm, Tala?

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

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

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