Magnetism + the Motor Effect (Topic 12)

Everything on the checklist for Magnetism + the Motor Effect (Topic 12)

What are the Two Types of Magnets?

• PERMANENT MAGNETS → ALWAYS produce a MAGNETIC FIELD

• INDUCED MAGNETS → ONLY produce a MAGNETIC FIELD when NEAR ANOTHER MAGNET (when in another Magnet’s Magnetic Field)

What are the Three Magnetic Materials?

• IRON

• NICKEL

• COBALT

What affects how Quickly a Magnet Loses its Magnetism?

SOFTNESS:

• e.g Steel is magnetically ‘HARD’ → Used in PERMANENT MAGNETS

• e.g Iron is magnetically ‘SOFT’ → Used in TEMPORARY MAGNETS

What are the Rules for Attraction + Repulsion?

• LIKE Poles REPEL

• OPPOSITE Poles ATTRACT

What is a Magnetic Field?

A REGION around a Magnet where OTHER MAGNETS experience a NON-CONTACT FORCE acting on them

How to Draw a Magnetic Field?

• Field Lines point TOWARDS SOUTH POLE

• MORE LINES = MORE STRENGTH

• Field lines get FURTHER APART when moving AWAY from Magnet

What does the Magnetic Field around a Bar Magnet look like?

• CLOSE FIELD LINES at POLES

What does the Magnetic Field around Two Opposite Poles look like?

UNIFORM FIELD:

• EVENLY SPACED

• PARALLEL

• STRAIGHT LINES

Why do Magnets Attract/Repel according to Magnetic Fields?

• Field Lines of OPPOSITE Poles POINT IN SAME DIRECTION → JOIN UP → ATTRACT

• Field Lines of LIKE POLES point in OPPOSITE DIRECTIONS → REPEL

How to Use a Plotting Compass to show the Field Lines of an Object?

1. Put PLOTTING COMPASS near Magnet

2. MARK DIRECTION of NEEDLE with a DOT

3. Move COMPASS to DOT you drew

4. Repeat STEPS 2 + 3 until back at Magnet → ONE FIELD LINE DRAWN

5. Repeat STEPS 1-4 until MULTIPLE Field Lines drawn

What does a Compass show about the Earth?

Compass ALWAYS points NORTH → Earth has a MAGNETIC FIELD → INNER CORE must be MAGNETIC

What is Electromagnetism?

MAGNETIC FIELD created by a CURRENT

What does the Magnetic Field around a Current-carrying Wire look like?

• CIRCLES

How to Work Out the Direction of the Magnetic Field in a Current-carrying Wire?

RIGHT HAND THUMB RULE:

Point THUMB in DIRECTION of CURRENT + CURL FINGERS → Direction of FINGERS is DIRECTION OF FIELD

What are the Two Factors that affect how Strong the Magnetic Field of a Current-Carrying Wire is?

• SIZE OF CURRENT

• DISTANCE FROM WIRE

How to Draw a Wire where the Current is Away/Towards you?

• Away - CROSS

• Towards - POINT

→ Like a DART (looks like X when Moving Away from you)

What is a Solenoid + What does its Magnetic Field look like?

• Solenoid → COIL of Wire

• Magnetic Field → Field Lines JOIN to form a STRONGER, ALMOST UNIFORM Field ALONG THE CENTRE

What are the Four Factors that affect how Strong the Magnetic Field of a Solenoid is?

• SIZE OF CURRENT

• DISTANCE FROM WIRE

• NUMBER OF TURNS

• IRON CORE in CENTRE of Solenoid → Becomes INDUCED MAGNET

What are (two) Uses of Permanent Magnets?

• COMPASS

• FRIDGE MAGNETS

What is a Use of Electromagnets?

• CRANES

What is the Motor Effect?

If you put a CURRENT-CARRYING WIRE through a MAGNETIC FIELD → the TWO MAGNETIC FIELDS INTERACT → FORCE on WIRE

What are the Three Factors that affect how Strong the Motor Effect is?

• Wire at RIGHT ANGLE to Magnetic Field → Strongest

• SIZE OF CURRENT

• STRENGTH OF MAGNETIC FIELD

What is the Formula for Size of the Force in the Motor Effect?

F = BIL

FORCE = MAGNETIC FLUX DENSITY (Strength of Magnetic Field) x CURRENT x LENGTH (of Wire in Magnetic Field)

How to Work Out the Direction of the Force of the Motor Effect?

FLEMING’S LEFT HAND RULE:

• THUMB is Direction of FORCE/MOTION

• FIRST FINGER is Direction of FIELD

• SECOND FINGER is Direction of CURRENT

How does a D.C Motor Work?

1. COIL of Wire (free to rotate) is placed in a MAGNETIC FIELD

2. DC Current flows through Wire → FORCE on EACH SIDE OF WIRE acts in DIFFERENT DIRECTION (due to Current being in Opposite Direction)

3. → COIL SPINS

4. EVERY HALF TURN (e.g when Vertical), the SPLIT RING COMMUTATOR SWITCHES the CONTACTS of the Loop → REVERSES CURRENT DIRECTION

5. → COIL SPINS in SAME DIRECTION

How to Switch the Direction of a Motor?

• SWAP CURRENT DIRECTION (e.g by swapping polarity)

• SWAP POLES OF MAGNET

How does a Loudspeaker Work?

1. COIL of Wire (free to rotate) is placed in a MAGNETIC FIELD

2. AC Current flows through Wire → FORCE produced which KEEPS SWITCHING DIRECTION

3. The Wire is connected to a PAPER CONE which also MOVES + KEEPS SWITCHING DIRECTION → SOUND WAVE

How is the Frequency of the Sound Wave produced by the Loudspeaker Controlled?

Same as the FREQUENCY of the AC Current