Forces in Everyday Devices - Middle School Physical Science

What is the function of the permanent magnet in many small electric motors?

It provides a steady magnetic field for the coil to push against. Creates the external magnetic field the coil interacts with.
What is the magnetic field produced around a current-carrying wire called?

An electromagnet (a magnetic field caused by electric current). Electric current creates a magnetic field around the wire.
What happens to the magnetic field direction if the current in a coil is reversed?

The magnetic field direction reverses. Reversing current flips the poles of the electromagnet.
What is an electromagnet?

A magnet produced by electric current in a coil. Electric current creates a magnetic field in the coil.
What device converts electrical energy into mechanical motion using magnetic forces?

An electric motor. Uses Lorentz force on current-carrying conductors.
What is an electromagnet (in terms of electricity and magnetism)?

A temporary magnet made by electric current in a coil. Current through a coil creates a magnetic field that disappears when current stops.
Which device converts mechanical motion into electrical energy using magnets and coils?

Electric generator. Spinning magnets near coils induces current flow.
Which change is required to induce current in a coil: constant field or changing field?

A changing magnetic field is required. Static fields don't induce current; only changes do.
What type of current is required for a basic transformer to work properly?

Alternating current (AC). DC produces no changing flux for induction.
What law states that a changing magnetic field induces an electric current in a conductor?

Electromagnetic induction (Faraday's law). Changing magnetic flux through a loop induces voltage.
What device converts mechanical motion into electrical energy using magnetism?

An electric generator. Rotating magnets induce current in coils through changing flux.
Which change increases induced current in a coil: moving the magnet faster or slower?

Moving the magnet faster. Faster change in magnetic flux induces more current.
What is the name of the force that causes charged objects to attract or repel each other?

Electric force. This force acts between objects with electric charge.
Which part of a microphone moves in a magnetic field to generate an electrical signal?

A coil (or conductor) attached to a vibrating diaphragm. Sound waves move coil in field, inducing voltage by Faraday's law.
Which change can strengthen an electromagnet: higher current or lower current?

Higher current. More current flow creates a stronger magnetic field.
What is the main purpose of a transformer in an electrical system?

To change AC voltage using electromagnetic induction. Uses two coils to step voltage up or down via induction.
Which device converts electrical energy into mechanical motion using magnets and current?

Electric motor. Uses magnetic forces on current-carrying coils to spin.
What is the key energy conversion in a microphone that uses induction?

Sound to electrical energy (motion induces a changing current). Vibrations move coil in field, inducing voltage.
What core material inside a coil most increases an electromagnet's strength?

Soft iron (ferromagnetic) core. Iron concentrates and amplifies the magnetic field.
What is the main function of a transformer in an electric power system?

It changes AC voltage using electromagnetic induction. Mutual induction between coils transfers energy.
Which device uses an electromagnet to switch a circuit on or off without direct contact?

Relay. Small current controls electromagnet to switch larger current.
What is the name for a coil of wire that creates a magnetic field when current flows?

Electromagnet (a current-carrying coil that acts like a magnet). Current through wire creates a magnetic field around it.
What common safety device uses an electromagnet to switch a circuit on or off (often in cars)?

A relay. Electromagnet pulls contacts to control another circuit.
Which change increases the strength of an electromagnet: higher current or lower current?

Higher current increases electromagnet strength. More current means stronger magnetic field from the coil.
Identify the energy conversion in an electric generator.

Mechanical (motion) energy to electrical energy. Rotating coils in magnetic field induce current via Faraday's law.
What is the magnetic field pattern around a straight current-carrying wire?

Concentric circles around the wire (right-hand rule direction). Moving charges create circular magnetic fields perpendicular to current flow.
What is the purpose of brushes in a simple DC motor?

They transfer current between the power source and the commutator. Sliding contacts that deliver power to rotating parts.
What is the main energy conversion in an electric generator?

Mechanical energy to electrical energy. Spinning motion induces current in wire coils.
Which change increases the strength of an electromagnet: more coil turns or fewer turns?

More coil turns increases electromagnet strength. Each turn adds to the total magnetic field strength.
What is a solenoid in the context of everyday devices?

A coil that becomes a magnet and can move a metal plunger. Current creates magnetic field to pull/push iron plunger.
Which common device uses an electromagnet to attract and move a metal armature to make sound?

Electric doorbell (or buzzer). Electromagnet pulls striker to hit bell repeatedly.
Which condition is required to induce current in a loop of wire near a magnet?

A changing magnetic field through the loop. Static fields don't induce current; only changing flux does.
What core material inside a coil most increases an electromagnet's strength?

A soft iron (ferromagnetic) core. Iron concentrates and amplifies the magnetic field lines.
What is the role of the iron core in an electromagnet?

It concentrates the magnetic field and makes it stronger. Iron's high permeability channels and amplifies magnetic flux.
Which change can strengthen an electromagnet: more coil turns or fewer coil turns?

More coil turns. More loops of wire increase the magnetic field strength.
Which common device uses an electromagnet to make a bell ring by repeated contact?

Electric doorbell (or electric buzzer). Electromagnet repeatedly attracts/releases striker to hit bell.
What does a transformer do to voltage using electromagnetic induction?

It increases or decreases AC voltage. Changing flux in primary coil induces voltage in secondary coil.
Identify the correct relationship for a simple transformer: $\frac{V_s}{V_p} = \frac{N_s}{N_p}$ .

$\frac{V_s}{V_p} = \frac{N_s}{N_p}$ . Voltage ratio equals turns ratio in ideal transformers.
Which device uses an electromagnet to attract a metal armature and move a switch?

Relay. Electromagnet pulls armature to close/open electrical contacts.
What is the main energy conversion in an electric motor?

Electrical energy to mechanical (motion) energy. Electric current creates forces that produce rotation.
Which device uses electromagnetic induction to increase or decrease voltage in AC circuits?

Transformer. Changing magnetic fields transfer energy between coils.
Which statement is correct: like magnetic poles attract or like magnetic poles repel?

Like poles repel; unlike poles attract. Same poles push apart; opposite poles pull together.
What happens to an electromagnet's strength when the number of coil turns increases?

It increases; more turns produce a stronger magnetic field. Each loop adds to the total magnetic field strength.
What is the term for producing current by moving a conductor through a magnetic field?

Electromagnetic induction. Changing magnetic flux through a conductor induces current.
What happens to an electromagnet when the current is turned off?

Its magnetic field largely disappears. No current means no magnetic field in electromagnets.
What is the name of the force that pushes or pulls on a current-carrying wire in a magnetic field?

Magnetic force on a current (motor effect). Current in a magnetic field experiences a force.
Identify the device that uses electromagnetic induction to convert sound waves into an electric signal.

A dynamic microphone. Sound vibrates coil in magnetic field, inducing current.
What force causes a current-carrying wire in a magnetic field to move?

A magnetic force on the moving charges in the wire. Lorentz force acts on current perpendicular to field.
Which option best describes what a loudspeaker does using electromagnets?

Current changes create motion of a coil/cone to produce sound. Varying current creates varying magnetic force to vibrate speaker cone.
Which action will induce current in a coil: holding a magnet still or moving it into the coil?

Moving the magnet into the coil. Motion creates changing flux; stationary magnets don't induce current.
Identify the device that uses an electromagnet to move a cone and produce sound.

A loudspeaker. Current through voice coil moves cone in magnetic field.
What happens to an electromagnet when the electric current is turned off?

Its magnetism greatly decreases or disappears. No current means no magnetic field is produced.
What is the name of the device that steps voltage up or down using induction between coils?

Transformer. Uses changing magnetic field to induce different voltage in second coil.
What is electromagnetic induction?

Producing current in a conductor by changing a magnetic field. Faraday's law: changing magnetic flux induces voltage.
What is the rule for how like and unlike electric charges interact?

Like charges repel; unlike charges attract. Same charges push apart; opposite charges pull together.
Which type of current is required for a typical transformer to work: AC or DC?

AC (alternating current). Needs changing flux; DC produces constant field.
What is the function of a speaker's electromagnet and permanent magnet together?

They move a cone back and forth to make sound. Changing current creates forces that vibrate the cone.
What is the main difference between a motor and a generator?

Motor: electrical to motion; generator: motion to electrical. Motors use electricity to move; generators use motion to make electricity.
Identify the direction of the magnetic field between a magnet's poles: from which pole to which pole?

From $N$ to $S$ (outside the magnet). Field lines exit north pole and enter south pole.
What happens to an electromagnet's strength when more turns of wire are added to the coil?

It increases (more turns produce a stronger field). Each loop adds to the total magnetic field.
What device uses an electromagnet to move a metal armature and ring a bell?

Electric doorbell (or buzzer). The electromagnet attracts and releases a striker repeatedly.
Which component in a simple DC motor reverses current every half-turn to keep it spinning?

The commutator (split ring). Switches current direction to maintain rotation.
Identify the key interaction that makes a motor spin: current in a coil interacts with what?

A magnetic field. The coil's field interacts with the permanent magnet's field.
What is the function of a microphone with a coil and magnet when sound vibrates the diaphragm?

It induces an electric signal from the vibrations. Motion in the magnetic field generates electrical signals.
What device uses a solenoid (electromagnet) to create motion, such as in a door lock or valve?

A solenoid actuator. Coil pulls iron plunger to create linear motion.
What is the formula for an ideal transformer relating voltage to turns?

$\frac{V_s}{V_p}=\frac{N_s}{N_p}$ . Voltage ratio equals turns ratio in ideal transformers.
Which core material usually makes an electromagnet stronger: iron core or plastic core?

Iron core. Iron concentrates and amplifies the magnetic field.
If a transformer has more turns on the secondary coil than the primary, what happens to voltage?

Voltage increases; it is a step-up transformer. Voltage ratio equals turns ratio in ideal transformers.
What device uses an electromagnet to pull a metal plunger and ring a bell when current flows?

An electric doorbell (electromagnetic bell). Electromagnet attracts striker to hit bell repeatedly.
If $N_s>N_p$ in a transformer, what happens to the voltage: step-up or step-down?

Step-up transformer (voltage increases). More secondary turns means higher secondary voltage.
In a simple circuit with a battery and wire coil, what must be true to create an electromagnet?

The circuit must be closed so current flows. A complete path allows electrons to flow through the coil.
What is the rule for how like and unlike magnetic poles interact?

Like poles repel; unlike poles attract. Same poles push apart; opposite poles pull together.
What device converts electrical energy into mechanical motion using magnetic forces?

An electric motor. Uses magnetic forces on current-carrying coils to create rotation.
What happens in a motor when current flows through a coil in a magnetic field?

A magnetic force creates torque that makes the coil rotate. Current in field experiences force perpendicular to both.
What is electromagnetic induction?

Producing current in a conductor by changing the magnetic field. Faraday's law: changing flux induces voltage.
Which part of a simple DC motor reverses the current every half-turn to keep it spinning?

Commutator (split-ring commutator). Switches current direction to maintain continuous rotation.
What is the purpose of an iron core inside a coil in an electromagnet?

It concentrates the field and makes the electromagnet stronger. Iron's high permeability amplifies the magnetic field.
What happens to an electromagnet's magnetic field strength when the current increases?

It increases (stronger magnetic field). More current means more magnetic field strength.
What does the right-hand rule tell you for a straight wire carrying current?

Thumb = current; curled fingers = magnetic field direction. Point thumb along current; fingers curl in field direction.
What device converts mechanical motion into electrical energy using induction?

A generator. Rotating coils in magnetic fields induce current.
What process produces current in a generator when a coil or magnet moves in a magnetic field?

Electromagnetic induction. Moving magnetic fields induce current in conductors.
Identify the energy conversion in an electric motor.

Electrical energy to mechanical (motion) energy. Current in magnetic field creates force that spins the motor.
Which type of current is required for a basic transformer to work: AC or DC?

AC. Only AC creates changing flux needed for induction.
What happens to the strength of an electromagnet when the current increases?

It increases; more current makes a stronger magnetic field. Magnetic field strength is proportional to current.
What is an electromagnet?

A magnet made by electric current flowing through a coil. Current through coiled wire creates a controllable magnetic field.
Which device uses a coil as an electromagnet to lift and drop a metal striker repeatedly?

Electric buzzer. Current turns on and off, making repeated clicking sounds.
What is the name of the force that causes a magnet to attract or repel another magnet?

Magnetic force. This force acts between magnets due to their magnetic fields.
Which device uses magnetic forces to lift and drop scrap metal by switching current on and off?

A crane electromagnet (industrial lifting magnet). Current control allows instant grip and release.
Which part of a speaker converts electrical signals into vibrations using magnets?

The voice coil interacting with a permanent magnet. Current through coil creates varying force, moving cone to produce sound.
What device uses an electromagnet to pull a switch closed to control another circuit?

Relay. The electromagnet pulls contacts together to complete a circuit.
If $N_s<N_p$ in a transformer, what happens to the voltage: step-up or step-down?

Step-down transformer (voltage decreases). Fewer secondary turns means lower secondary voltage.

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