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.

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

   25 paper clips
4. 3.

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

   • 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
   • Use 1, 2 and 3 batteries with the same coil and nail, repeating each
   • Use 1, 2 and 3 batteries, but with a different nail each time

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?

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

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?

   • Coils and core both changed, so either could explain the jump
   • The nail should have been aluminum
   • The test should have changed the batteries as well, to test everything
   • Nails do not change an electromagnet
9. 6.

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

   • A compass needle turns when a magnet is near but not touching
   • A paper clip stays stuck to a magnet once it touches it
   • A magnet sticks to a metal fridge door when it touches it
   • A bar magnet feels heavy for its size when it is lifted
10. 7.

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

    • More wire is heavier, so it pulls harder on the clips
    • Each loop adds its own magnetic field, and the fields add up
    • 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?

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

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?

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

14. Pull on a steel ball (example data)

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

15. 10.

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

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