Omar investigated how the number coils around an iron core affects the strength of an electromagnet. He measured the strength by measuring how many paper clips it picked up. He obtained the results in given table.

Number of coils	Number of paper clips picked up
$0$	$0$
$10$	$3$
$20$	$12$
$30$	$19$
$40$	$25$
$50$	$30$
$60$	$34$

 

Here are magnetic fields around two pairs of magnets.

Which two magnets are attracted?

Here are magnetic fields around two pairs of magnets.

Which two magnets are repelling?

Draw the field around two magnets south poles facing each other.

Sarah did an investigation into how the type of core in an electromagnet affects its strength. She measured how many paper clips each picked up. She obtained the results shown in table.

What was the independent variable in this investigation?

Sarah did an investigation into how the type of core in an electromagnet affects its strength. She measured how many paper clips each picked up. She obtained the results shown in table.

What was the dependent variable in this investigation?

Sarah did an investigation into how the type of core in an electromagnet affects its strength. She measured how many paper clips each picked up. She obtained the results shown in table.

Name one control variable in this investigation?

Sarah did an investigation into how the type of core in an electromagnet affects its strength. She measured how many paper clips each picked up. She obtained the results shown in table.

Steel is a mixture of iron and carbon. Predict how many paper clips a steel core could pick up. Explain your answer.

Use the diagram to explain how an electric bell works.