Primary 3 Science · Answers and explanations
Making Magnets: Investigation Practice
Use this page to check the worksheet together. Talk about why each answer is right. Total: 20 marks.
Section A · Multiple choice 8 marks
1. Look at Table 1. How many steel clips did the nail attract after 30 strokes?1 mark
Table 1: Steel nail stroked with the north pole of a magnet
| Number of strokes | Steel clips attracted |
|---|
| 10 | 2 |
| 20 | 5 |
| 30 | 7 |
| 40 | 10 |
(A) 5(B) 7(C) 10(D) 30
Answer: (B) 7Read across from 30 strokes in the table: the nail attracted 7 clips.
2. Which conclusion matches Table 1?1 mark
Table 1: Steel nail stroked with the north pole of a magnet
| Number of strokes | Steel clips attracted |
|---|
| 10 | 2 |
| 20 | 5 |
| 30 | 7 |
| 40 | 10 |
(A) The more strokes, the more clips attracted, so the stronger the magnet(B) The more strokes, the fewer clips attracted(C) The number of strokes does not change the number of clips(D) The nail is strongest after only 10 strokes
Answer: (A) The more strokes, the more clips attracted, so the stronger the magnetThe clips go up 2, 5, 7, 10 as the strokes go up, so more strokes make a stronger magnet.
3. Meena wants to find out if the number of strokes changes how strong a steel nail becomes. Which variable must she keep the same?1 mark
(A) The number of strokes(B) The number of clips attracted(C) The strength of the nail after the test(D) The direction of the strokes
Answer: (D) The direction of the strokesShe changes the number of strokes and measures the clips attracted. Everything else, such as the direction of the strokes, must stay the same.
4. Zara wants to turn a steel needle into a magnet by the stroke method. Which is the correct way to stroke?1 mark
(A) Rub the magnet back and forth along the needle(B) Use the north pole going one way and the south pole coming back(C) Use the same pole and the same direction every time(D) Stroke the needle with a piece of wood
Answer: (C) Use the same pole and the same direction every timeAlways use one pole of the magnet and always move the same way, lifting the magnet up and back through the air between strokes.
5. Look at Table 2. How many more clips did the electromagnet attract with 40 turns than with 10 turns?1 mark
Table 2: Iron nail, 1 battery, different turns of wire
| Turns of wire | Steel clips attracted |
|---|
| 10 | 3 |
| 20 | 6 |
| 30 | 9 |
| 40 | 12 |
(A) 3(B) 9(C) 6(D) 12
Answer: (B) 940 turns attracted 12 clips and 10 turns attracted 3 clips. 12 - 3 = 9.
6. Look at Table 3. Which two set-ups give a fair test to find out if the number of turns of wire changes the strength of the electromagnet?1 mark
Table 3: Four electromagnet set-ups (all use the same type of iron nail and the same clips)
| Set-up | Turns of wire | Batteries |
|---|
| P | 10 | 1 |
| Q | 20 | 1 |
| R | 20 | 2 |
| S | 30 | 3 |
(A) P and Q(B) P and R(C) Q and S(D) R and S
Answer: (A) P and QIn P and Q only the turns of wire are different (10 and 20). The batteries and nail are the same. In the other pairs both turns and batteries are different.
7. After lifting some clips, Mei finds that the wires and nail feel warm. What should she do first?1 mark
(A) Add another battery(B) Wind more wire onto the nail(C) Touch the bare wires to check how hot they are(D) Disconnect the wire from the battery
Answer: (D) Disconnect the wire from the batteryWires can get hot when connected for a long time. Disconnect the battery promptly to stay safe.
8. A scrapyard crane uses an electromagnet to lift old cars. Why is an electromagnet better than an ordinary magnet for this job?1 mark
(A) It attracts wood and plastic too(B) It does not need electricity(C) Its magnetism can be switched off to drop the car(D) Its poles repel iron so the car floats
Answer: (C) Its magnetism can be switched off to drop the carWhen the current is switched off the electromagnet stops attracting, so the crane can put the car down.
Section B · Show what you know 12 marks
9. Look at Table 5. Name the variable that Mei changed and the variable that she measured.2 marks
Table 5: Iron nail with 20 turns of wire
| Number of batteries | Steel clips attracted |
|---|
| 1 | 6 |
| 2 | 10 |
| 3 | 14 |
Answer: Changed: the number of batteries (1 mark). Measured: the number of steel clips attracted (1 mark).She changed the batteries (1, 2, 3) and counted the clips to measure the strength.
10. Dan says, "More strokes make a weaker magnet." Look at Table 4. Is Dan's test a fair test? Explain.2 marks
Table 4: Dan's results
| Test | Number of strokes | How the nail was stroked | Clips attracted |
|---|
| 1 | 10 | same pole, same direction every time | 3 |
| 2 | 30 | back and forth, using both ends of the magnet | 1 |
Answer: No (1 mark). He changed two things, the number of strokes and the way of stroking, so we cannot tell which one caused the result (1 mark).A fair test changes only one variable. Dan changed the strokes and the direction at the same time.
11. Mei tried 20 turns of wire three times, as in Table 6. Why did she repeat the test? What do her results tell her?2 marks
Table 6: Iron nail, 20 turns of wire, 1 battery
Answer: To get more reliable results (1 mark). The results are close (6, 7 and 6), so she can trust them (1 mark).Repeating a test checks that the result was not a mistake or luck.
12. Use Table 2 to predict the number of clips for 50 turns of wire. Give a reason for your prediction.2 marks
Table 2: Iron nail, 1 battery, different turns of wire
| Turns of wire | Steel clips attracted |
|---|
| 10 | 3 |
| 20 | 6 |
| 30 | 9 |
| 40 | 12 |
Answer: Accept 14 to 16 (1 mark). The clips go up by about 3 for every 10 more turns, or more turns give more clips (1 mark).The clips went 3, 6, 9, 12, so the next would be 15.
13. Ali made the electromagnet shown. It attracts only 1 clip. Suggest two ways to make it stronger.2 marks
Answer: Wind more turns of wire around the nail (1 mark). Use more batteries (1 mark).More turns of wire and more batteries both make an electromagnet stronger.
14. Look at the bar chart. Which two set-ups show the effect of the number of batteries? What does the chart show about batteries?2 marks
Answer: Y and Z (1 mark). More batteries make the electromagnet stronger, so it attracts more clips (1 mark).Y and Z both have 30 turns. Only the batteries are different, and Z with 2 batteries attracted more clips.
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