AQA Physics 8463 Section 4.7 Magnetism and Electromagnetism

A complete set of 71 vocabulary flashcards covering AQA Physics Section 4.7: Magnetism and Electromagnetism.

Magnet

An object that produces a magnetic field and has north and south poles.

Magnetic Poles

The two ends of a magnet, designated as north and south.

Like Magnetic Poles Interaction

Like magnetic poles repel each other.

Unlike Magnetic Poles Interaction

Unlike magnetic poles attract each other.

Permanent Magnet

A magnet that produces its own magnetic field.

Induced Magnet

A material that becomes magnetic when placed in a magnetic field.

Induced Magnetism Behavior

It is usually lost quickly when the inducing magnet is removed.

Permanent and Induced Magnet Force

The force between a permanent magnet and an induced magnet is always attraction.

Magnetic Field

The region around a magnet where a magnetic material or another magnet experiences a force.

Magnetic Field Line Direction

Points from the north pole to the south pole outside a magnet.

Strongest Field Region of a Bar Magnet

Located at its poles, where the magnetic field lines are closest together.

Plotting Compass

An instrument used experimentally to show the direction of a magnetic field.

Compass Needle Alignment

Its north-seeking pole points in the direction of the magnetic field.

Earth's Magnetic Field

The natural magnetic field of the Earth that causes compasses to align in a north-south direction.

Current-Carrying Wire Effect

A magnetic field is produced around any wire carrying an electric current.

Field Shape Around Straight Wire

Concentric circles around the current-carrying wire.

Field Strength vs Current

Increasing the electric current through a wire makes the magnetic field stronger.

Field Strength vs Distance

Magnetic field strength decreases as distance from a current-carrying wire increases.

Right-Hand Grip Rule

A rule used to find the direction of the magnetic field around a current-carrying wire.

Solenoid

A coil of wire carrying electric current.

Solenoid Magnetic Field

Similar to the field of a bar magnet, featuring a strong, nearly uniform field inside.

Strengthening a Solenoid Field

Can be done by increasing the current, increasing the number of turns per unit length, or adding an iron core.

Electromagnet

A solenoid with a magnetic core, usually iron, whose magnetic field is produced by an electric current.

Electromagnet Advantage

Can be switched on and off, and its field strength can be changed.

Motor Effect

A force acting on a current-carrying conductor placed in a magnetic field.

Maximum Motor Effect Force

Occurs when the current-carrying conductor is perpendicular to the magnetic field.

Zero Motor Effect Force

Occurs when the current-carrying conductor is parallel to the magnetic field.

Motor Effect Force Equation

$$F = B I l$$

Symbol $B$ in Motor Effect

Magnetic flux density, measured in tesla, $T$.

Symbol $I$ in Motor Effect

Current, measured in amperes, $A$.

Symbol $l$ in Motor Effect

Length of conductor in the magnetic field, measured in metres.

Tesla ($T$)

The unit of measurement for magnetic flux density.

Fleming's Left-Hand Rule

Determines the direction of force on a current-carrying conductor in a magnetic field.

First Finger (Fleming's Left-Hand Rule)

Represents the magnetic field direction, pointing from north to south.

Second Finger (Fleming's Left-Hand Rule)

Represents conventional current direction.

Thumb (Fleming's Left-Hand Rule)

Represents the direction of force or motion.

Electric Motor Mechanism

Forces on current-carrying conductors in a magnetic field produce a turning effect on a coil.

Current Reversal in Motor Effect

Reverses the direction of the acting force.

Magnetic Field Reversal in Motor Effect

Reverses the direction of the acting force.

Increasing Motor Effect Force

Can be achieved by increasing magnetic flux density, current, or length of conductor in the field.

Electromagnetic Induction

Producing a potential difference across a conductor when it cuts magnetic field lines or the magnetic field through it changes.

Generator Effect

The induction of a potential difference when a conductor moves relative to a magnetic field.

Induced Current Condition

Flows when the conductor is part of a complete circuit and an induced potential difference is produced.

Increasing Induced Potential Difference

Achieved by moving the conductor or magnet faster, using a stronger magnetic field, or increasing turns in a coil.

Motion Reversal in Induction

Reverses the direction of the induced potential difference.

Field Reversal in Induction

Reverses the direction of the induced potential difference.

Lenz's Law

States that the induced current produces a magnetic field that opposes the change that caused it.

Energy Conservation in Induction

Work must be done against the opposing effect of the induced current; energy transferred electrically comes from that work.

Alternator

A device that produces alternating potential difference and alternating current.

Dynamo

A device that produces direct potential difference and direct current.

Slip Rings vs Split-Ring Commutator

Slip rings maintain alternating output, whereas a split-ring commutator reverses connections to produce a direct output.

Microphone

A device that converts pressure variations in sound waves into variations in electric current.

Moving-Coil Microphone Mechanism

Sound waves move a diaphragm and coil in a magnetic field, inducing a changing potential difference.

Loudspeaker

A device that converts variations in electric current into sound waves.

Loudspeaker Mechanism

A changing current in a coil in a magnetic field produces changing forces, vibrating a cone to create sound waves.

Transformer

A device that changes the potential difference of an alternating supply using electromagnetic induction.

Main Parts of a Transformer

A primary coil, secondary coil, and an iron core.

AC Requirement for Transformers

A changing current produces a changing magnetic field, which induces a potential difference in the secondary coil.

Step-Up Transformer

A transformer that increases potential difference.

Step-Down Transformer

A transformer that decreases potential difference.

Transformer Equation

$$\frac{V_p}{V_s} = \frac{N_p}{N_s}$$

Symbols $N_p$ and $N_s$

Represent the number of turns on the primary ($N_p$) and secondary ($N_s$) coils of a transformer.

Step-Up Transformer Turns Ratio

The secondary coil has more turns than the primary coil.

Step-Down Transformer Turns Ratio

The secondary coil has fewer turns than the primary coil.

100% Efficient Transformer Power Relation

$$V_p I_p = V_s I_s$$

Current Reduction in Step-Up Transformers

Input and output power are equal, so stepping up potential difference requires a lower current.

High Potential Difference in National Grid

Allows the same power to be transferred with lower current, reducing heating losses in transmission cables.

Permanent Magnet vs Electromagnet

A permanent magnet produces a field without current; an electromagnet field is produced by current and can be controlled.

Motor Effect vs Generator Effect

Motor effect uses current and a magnetic field to produce force; generator effect uses movement or changing fields to produce potential difference.

Fleming's Left-Hand Rule Initial Step

Identify the magnetic field direction and conventional current direction first.

Prerequisite Check for $F = B I l$

Ensure the length of conductor used is within the magnetic field and perpendicular to the field.