Magnets, magnetic fields and electromagnets

Answer Key - Grade 8 Science Worksheet - Building Confidence

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	4
   20	8
   30	12

2. 1.

   The pattern in the table continues. How many clips would Ari's electromagnet lift with 70 coils?

   28 paper clips
3. 2.

   If the pattern in the table continues, how many clips would Esme's electromagnet lift with 70 coils?

   42 paper clips

4. Use this

   Field diagram of a bar magnet, N pole on the left and S pole on the right. Field lines leave the N pole, curve around outside the magnet and enter the S pole; arrows on the lines point from N to S. Point A is 1 cm from the N pole, where the lines are close together. Point B is 6 cm above the middle of the magnet, where the lines are far apart.

5. 3.

   Where is the field stronger, and how do you know, Jun?

   • At B, since its lines spread over a larger area
   • At A, since the lines are close together there
   • At B, since it is above the middle of the magnet
   • The same at both, since field lines cannot cross

6. Use this

   Field diagram of a bar magnet, N pole on the left and S pole on the right. Field lines leave the N pole, curve around outside the magnet and enter the S pole; arrows on the lines point from N to S. The compass is 2 cm to the left of the N pole.

7. 4.

   Which way does the compass needle's north end point, and why, Kira?

   • Up the page, to the geographic North Pole
   • Away from the magnet's N pole, along the field lines
   • Toward the magnet's N pole, since a north end is pulled to north
   • It keeps spinning, since two poles are near
8. 5.

   What will these two magnets do, and what in the diagram shows it, Luz?

   • Pull together, since both of the facing ends are N poles
   • Pull together until the field lines cross in the gap
   • Push apart: the lines from the two N poles bend away
   • Nothing happens, since the lines do not meet in the gap

9. What a magnet picks up (example data)

   object	material	picked up
   paper clip	steel	yes
   nail	iron	yes
   foil	aluminum	no
   wire	copper	no
   spoon	plastic	no
   pencil	wood	no

10. 6.

    Which statement does the table support, Milo?

    • It picked up only the iron and steel objects
    • A magnet picks up only the shiny, smooth objects
    • A magnet picks up every metal object it touches
    • A magnet picks up only the small, light objects
11. 7.

    Noah adds an iron washer and an aluminum washer to the test. What should the magnet do, using the table?

    • Pick up neither, since washers are small
    • Pick up the iron washer but not the aluminum one
    • Pick up the aluminum washer, since it is lighter
    • Pick up both, since both are metal

12. A paper clip near a magnet (example data)

    distance from the magnet (cm)	clip jumps to the magnet
    1	yes
    2	yes
    4	no
    8	no

13. 8.

    What does the table show about the magnet's pull on a paper clip, Pia?

    • The pull is the same at each distance tested
    • It acts across a gap and weakens with distance
    • The pull gets stronger the farther away the clip is
    • The pull works just when the clip touches the magnet
14. 9.

    Two bar magnets push apart with their ends facing. Ren turns one magnet around. What happens, and why?

    • They pull together: now unlike poles face each other
    • They spin around each other without touching
    • They push apart the same, since turning does not change poles
    • They push apart harder, since the poles now face the other way
15. 10.

    Can Tala cut a bar magnet to get a piece with just an N pole?

    • Yes, by cutting off the N end of the magnet
    • Yes, by cutting the magnet exactly in the middle
    • No: every piece has both an N and an S pole
    • Yes, by grinding off the S end of the magnet