Magnets, magnetic fields and electromagnets

Answer Key - Grade 8 Science Worksheet

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

1. Read this first

   Teacher's electromagnet test (example data)

   coils	batteries	paper clips lifted
   10	1	4
   20	1	8
   10	2	8

2. 1.

   Each change multiplies the clips lifted. How many clips would Ari's electromagnet lift with 20 coils and 2 batteries together?

   16 paper clips
3. 2.

   Each change multiplies the clips lifted. How many clips would the electromagnet lift with 20 coils and 3 batteries together, Esme?

   36 paper clips
4. 3.

   Which two rows are a fair test of the iron core alone, Jun?

   • Rows 2 and 3, since only the core changes
   • Rows 1 and 3, since they show the smallest and a large result
   • Rows 4 and 5, since they have the biggest difference
   • Rows 3 and 4, since both have an iron nail
5. 4.

   Which two rows are a fair test of the number of coils alone, Kira?

   • Rows 5 and 6, since both rows have 10 coils
   • Rows 1 and 2, since only the coils change
   • Rows 2 and 4, since both rows have 20 coils
   • Rows 1 and 3, since row 3 has 20 coils and a core
6. 5.

   Which two rows are a fair test of the number of batteries alone, Luz?

   • Rows 4 and 5, since row 4 has 2 batteries in it
   • Rows 5 and 6, since only the batteries change
   • Rows 2 and 3, since both rows have 1 battery
   • Rows 1 and 6, since they show the biggest change
7. 6.

   Which model of the field fits all four compass readings, Milo?

   • Field lines run from the S pole to the N pole outside the magnet
   • Lines leave the N pole, curve outside and enter the S pole
   • Field lines go straight out from the magnet in each direction
   • There is no field outside the magnet; the needle just points north
8. 7.

   Which model fits all three compass readings between the two magnets, Noah?

   • Each magnet's field stops at that magnet's own end, without reaching the gap
   • The magnets do not affect each other, so the needle ignores them both
   • The lines run from one magnet across to the other, as if N faced S
   • Each N pole pushes its lines away; the field is near zero in the middle

9. Pull on a paper clip (example data)

   distance from the magnet (cm)	pull (N)
   1	8.0
   2	2.0
   4	0.5

10. 8.

    Which statement does the force data support best, Pia?

    • Doubling the distance cuts the pull to a quarter
    • The pull halves each time the distance doubles again
    • The pull is zero at any distance beyond 1 cm
    • The pull is the same at each distance in the table
11. 9.

    Far from magnets, a compass's north end points toward Earth's northern magnetic pole. What kind of magnet pole must it be, Tala?

    • An N pole, since like poles attract each other
    • It acts like an S pole, since unlike poles attract
    • An N pole, since the needle's north end points to it
    • Neither, since Earth is not a magnet and has no poles

12. Electromagnet with an iron nail (example data)

    battery connected	paper clips lifted	compass needle moves
    yes	14	yes
    no	0	no

13. 10.

    What does the table show about the electromagnet's field, Zee?

    • The nail is a permanent magnet whatever the battery does
    • The coil stores magnetism after the battery is off
    • The battery itself is the magnet that lifts the clips
    • The field depends on the current; with it off, clips drop