Magnets and Magnetic field and force Facts about

Magnets and Magnetic field and force

Facts about magnets Not all materials are attracted to a magnet. Only ferromagnetic materials are attracted to a magnet. Examples of ferromagnetic materials are iron, nickel, and cobalt.

Facts about magnets Different magnets have different strengths. The strength of the magnet does not necessarily depend on the size of the magnet. The strength of the magnetic depends on the alignment of the magnetic domains in the magnet.

Facts about magnets The magnetic domains act as tiny magnets within a magnet. The more the magnetic domains point in the same direction, the stronger the magnetic field of the magnet.

Facts about magnets Magnets have 2 poles (north and south) Like poles repel Unlike poles attract Magnets create a MAGNETIC FIELD around them

Facts about magnets When a bar magnet is broken into smaller pieces, each small piece will have its own north and south pole.

Magnetic field of a bar magnet

Magnetic Field A bar magnet has a magnetic field around it. This field is 3 D in nature and often represented by lines LEAVING north and ENTERING south To define a magnetic field you need to understand the MAGNITUDE and DIRECTION We sometimes call the magnetic field a B-Field as the letter “B” is the SYMBOL for a magnetic field with the TESLA (T) as the unit.

Magnetic field The magnetic field of a bar magnet is strongest at the poles.

Facts about magnets When suspended, a bar magnet will align itself with the Earth’s magnetic field. The north pole of the magnet points toward the north geographic pole of the Earth.

Magnetic field between like poles

Magnetic field between unlike poles

Draw the magnetic field lines between the two south poles N S S N

Directional compass The needle of a compass is a bar magnet. The tip of the compass needle that points to the north direction is the north pole of the compass needle.

Earth’s geographic and magnetic poles

Permanent magnets vs Electromagnets Permanent magnets retains a magnetic force Can not be turned on and off Electromagnets Use electricity to create a magnetic field They can be controlled (turned on and off) Their force or strength of field can be controlled

Strength of the magnetic field As the distance of a point from the magnet increases, the magnetic field due to the magnet at that point decreases.

Comparison between gravitational, electric and magnetic forces Field The force is applied on a: Direction of the force Gravitational field mass same direction as the field Electrical force electric charge opposite or in the same direction as the field Magnetic field electric charge perpendicular to the plane created by v and B

Direction of the magnetic force? Right Hand Rule To determine the DIRECTION of the force on a POSITIVE charge we use a special technique that helps us understand the 3 D/perpendicular nature of magnetic fields. Basically you hold your right hand flat with your thumb perpendicular to the rest of your fingers • The Fingers = Direction B-Field • The Thumb = Direction of velocity • The Palm = Direction of the Force For a NEGATIVE charge the force is in the opposite direction (where the back of your hand is facing)

Magnetic force on a moving charge: Another version of right-hand rule

Our direction guides up +z in: west south in: -x north -y out: east +y out: +x up down in: in left -z right out: out down

Magnetic force on a moving charge

Charges moving in a wire Up to this point we have focused our attention on PARTICLES or CHARGES only. The charges could be moving together in a wire. Thus, if the wire had a CURRENT (moving charges), it too will experience a force when placed in a magnetic field. You simply used the RIGHT HAND ONLY and the thumb will represent the direction of the CURRENT instead of the velocity.

Magnetic force on current-carrying wire

Example 0. 0396 N into the page A 36 -m length wire carries a current of 22 A running from right to left. Calculate the magnitude and direction of the magnetic force acting on the wire if it is placed in a magnetic field with a magnitude of 0. 50 x 10 -4 T and directed up the page.

Direction of magnetic force on current-carrying wire