Magnets, magnetic fields and electromagnets

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. Read this first

   Teacher's electromagnet test (example data)

   coils	paper clips lifted
   10	3
   20	7
   30	11
   40	15

2. 1.

   The clips lifted keep rising in the same steps. How many clips would Ari's electromagnet lift with 70 coils?

   27 paper clips
3. 2.

   The clips lifted keep rising in equal steps. How many clips would Bo's electromagnet lift with 60 coils?

   37 paper clips
4. 3.

   If the steps in the table stay equal, how many clips would the electromagnet lift with 80 coils, Esme?

   25 paper clips
5. 4.

   Jun wants to test whether more batteries make an electromagnet stronger. Which plan is best?

   • Use 1, 2 and 3 batteries, but with a different nail each time
   • Use 1, 2 and 3 batteries with the same coil and nail, repeating each
   • Use 1, 2 and 3 batteries with 10, 20 and 30 coils, to save a lot of time
   • Use 1, 2 and 3 batteries once each, and then trust the first results

6. Use this

   Investigation card (test results). Changed: number of coils. Measured: paper clips lifted. Kept the same: same nail, same battery, one trial for each setup. 10 coils: 3. 20 coils: 7. 30 coils: 11.

7. 5.

   Which conclusion is best supported by this test, Kira?

   • More coils lifted more clips here; each setup needs repeating
   • More coils lifted fewer clips, so fewer coils are better
   • Coils made no difference, since the numbers are small
   • Shown for any nail and any battery, so no repeat is needed

8. Use this

   Investigation card (test results). Changed: coils and core. Measured: paper clips lifted. Kept the same: 1 battery. 10 coils, no core: 2. 30 coils, iron nail: 19.

9. 6.

   Luz says the iron nail caused the jump in clips. Why is that not supported by this test?

   • Coils and core both changed, so either could explain the jump
   • The test should have changed the batteries as well, to test everything
   • The nail should have been aluminum
   • Nails do not change an electromagnet
10. 7.

    Which observation is the strongest evidence that a magnetic field acts between objects that are not touching, Milo?

    • A paper clip stays stuck to a magnet once it touches it
    • A compass needle turns when a magnet is near but not touching
    • A bar magnet feels heavy for its size when it is lifted
    • A magnet sticks to a metal fridge door when it touches it
11. 8.

    Which model best explains why more coils make an electromagnet stronger, Noah?

    • More wire is heavier, so it pulls harder on the clips
    • More coils block the iron core's field from reaching clips
    • Each loop adds its own magnetic field, and the fields add up
    • More coils store more of the battery's energy for later
12. 9.

    An iron nail lifts 15 clips; with no core the coil lifts 4. Which model best explains the nail's effect, Pia?

    • The coil's field magnetizes the iron, which adds its own field
    • Iron is heavy, so it drags the clips up
    • Iron stores the battery's electricity
    • Iron is a permanent magnet already, so it works without a battery

13. Compass at the coil's right end (example data)

    battery connection	needle's north end points
    normal	away from the coil
    reversed	toward the coil

14. 10.

    Zee says an electromagnet's poles are fixed, like a bar magnet's. What does the table show?

    • Disagree: the poles disappeared when it was reversed
    • Agree: the compass needle just points north anyway
    • Agree: the same coil is the same kind of magnet each time
    • Disagree: reversing the current swapped the poles