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. 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.

6. 4.

   Which conclusion is best supported by this test, Kira?

   • Shown for any nail and any battery, so no repeat is needed
   • 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

7. 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.

8. 5.

   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 test should have changed the batteries as well, to test everything
   • Coils and core both changed, so either could explain the jump
   • The nail should have been aluminum
9. 6.

   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 bar magnet feels heavy for its size when it is lifted
   • A compass needle turns when a magnet is near but not touching
   • A magnet sticks to a metal fridge door when it touches it
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 store more of the battery's energy for later
    • More coils block the iron core's field from reaching clips
11. 8.

    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 is a permanent magnet already, so it works without a battery
    • Iron stores the battery's electricity

12. Pull on a steel ball (example data)

    distance from the magnet (cm)	pull (N)
    3	6.0
    6	1.5
    12	0.4

13. 9.

    Tala says the pull at 6 cm is half the pull at 3 cm. Is that right?

    • No: 1.5 N is a quarter of 6.0 N, not a half
    • Yes: 6 cm is double 3 cm, so the pull halves
    • No: the pull is the same at both distances
    • Yes: 1.5 N is small compared with 6.0 N

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: 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