Magnetism
Primary 6 · Science and Elementary Technology
Magnetism
Lesson 4 of 6
15 min
Let's begin
Ishimwe's teacher lays a sheet of white paper over a bar magnet and gently sprinkles grey iron filings on top. She taps the paper softly.
Like magic, the filings slide into curved lines that loop from one end of the magnet to the other. "You are looking at something invisible," the teacher says. "This is the magnet's field."
The magnetic field is the space around a magnet where its force can be felt. Inside this space, the magnet can attract magnetic materials and push or pull other magnets. The field is invisible, but we can show its shape.
The filings crowd thickly around the two poles and form curved lines that run from one pole to the other.
Scientists draw the field with magnetic field lines:
A compass needle is a tiny magnet, so it turns to line up with the field. Put a small compass at different places around a bar magnet and draw an arrow in the direction the needle points. Join the arrows, and you get the field lines.
With unlike poles facing each other, the lines run straight across the gap from one magnet to the other: the magnets attract. With like poles facing, the lines bend away from each other and leave an empty spot in the middle: the magnets repel. You saw both patterns in the last lesson.
The Earth has a magnetic field too, as if a huge bar magnet were buried inside it. That is why a compass needle, anywhere in the world, turns to point north.
Open the Magnet and Compass simulation. Drag the bar magnet around and watch the compass needle turn to follow the field. Try the options to show the field all around the magnet, to look inside the magnet, and to flip its poles. What happens to the compass when you flip the poles?
Tip
Field lines leave from North and come home to South
Where the lines crowd together, the field is strong; where they spread out, it is weak.
Try each one on your own first, then tap Show answer to check.
What is a magnetic field?
Answer: The space around a magnet where its magnetic force can be felt.
Where are the field lines closest together around a bar magnet?
Answer: At the poles, where the field is strongest.
In which direction do field lines point outside a magnet?
Answer: From the north pole to the south pole.
Describe the pattern of iron filings between two like poles.
Answer: The filings bend away from each other and leave an empty gap in the middle, showing that the magnets repel.
Why does a compass needle move when you bring it near a magnet?
Answer: The needle is a small magnet, so it turns to line up with the magnet's field.
What you learned today
Sources and credits
Quick check
Put the steps for showing a magnet's field with iron filings in order.
Tap the cards in the right order.
