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 10, 20 and 30 coils, to save a lot of time
   • Use 1, 2 and 3 batteries with the same coil and nail, repeating each
   • 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
   • Coils made no difference, since the numbers are small
   • More coils lifted fewer clips, so fewer coils are better
   • 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?

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

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

    • Each loop adds its own magnetic field, and the fields add up
    • More wire is heavier, so it pulls harder on the clips
    • More coils block the iron core's field from reaching clips
    • More coils store more of the battery's energy for later
11. 8.

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

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

12. Electromagnet with an iron nail (example data)

    batteries	paper clips lifted
    1	15
    2	25
    3	33

13. 9.

    Ren says doubling the batteries doubles the clips lifted. What does the table show?

    • Agree: 2 batteries gave more clips than 1 battery did
    • Agree: adding more batteries doubles the clips each time
    • Disagree: batteries make no difference to the clips
    • Disagree: 15 to 25 is about 1.7 times, not 2 times

14. 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

15. 10.

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

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