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Magnets and electromagnets
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Magnets can push and pull without touching. An electric current can also make a magnet that you can switch on and off.
Magnets and fields
A magnet has a north pole and a south pole. Like poles repel; unlike poles attract.
Only a few materials are magnetic: iron, nickel, cobalt, and steel (which contains iron).
A magnet has a magnetic field around it. We draw field lines going from north to south. Lines close together show a stronger field. A compass needle lines up with the field, so you can use it to plot field lines.
Only a few materials are magnetic: iron, nickel, cobalt, and steel (which contains iron).
A magnet has a magnetic field around it. We draw field lines going from north to south. Lines close together show a stronger field. A compass needle lines up with the field, so you can use it to plot field lines.
The Earth's magnetic field
The Earth behaves as if it has a giant bar magnet inside it.
A compass needle's north pole points towards the Earth's geographic North, which helps people navigate.
(This means the magnetic pole near the geographic North Pole is really a magnetic south pole: unlike poles attract.)
A compass needle's north pole points towards the Earth's geographic North, which helps people navigate.
(This means the magnetic pole near the geographic North Pole is really a magnetic south pole: unlike poles attract.)
Electromagnets and motors
A current in a wire makes a magnetic field around it.
An electromagnet is a coil of wire with a current. Its field is like a bar magnet's, and it can be switched off.
To make it stronger: add more turns of wire, use a bigger current, or put an iron core inside the coil.
Uses: lifting scrap iron, electric door locks, electric bells.
In a DC motor, a coil carrying a current sits in a magnetic field. The forces on the coil make it spin.
An electromagnet is a coil of wire with a current. Its field is like a bar magnet's, and it can be switched off.
To make it stronger: add more turns of wire, use a bigger current, or put an iron core inside the coil.
Uses: lifting scrap iron, electric door locks, electric bells.
In a DC motor, a coil carrying a current sits in a magnetic field. The forces on the coil make it spin.
Give three ways to make an electromagnet pick up more paper clips.
- Wind more turns of wire on the coil.
- Increase the current.
- Put an iron core in the coil.
Answer: More turns, a bigger current, and an iron core.
Like poles repel; unlike poles attract. Iron, nickel and cobalt are magnetic. Field lines run north to south. A current makes a magnetic field; an electromagnet is stronger with more turns, more current and an iron core. A motor uses this to spin.
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