electromagnetism and EM waves

• What are the two poles of a magnet?

North pole and south pole.

• What happens when like magnetic poles are brought together?

They repel each other.

• What happens when opposite magnetic poles are brought together?

They attract each other.

• What happens when a magnet is broken in half?

Each half becomes a smaller magnet with its own north and south poles.

• What are ferromagnetic materials?

Materials that are strongly attracted to magnets, such as iron.

• What happens when iron is placed near a magnet?

It becomes temporarily magnetized and is attracted to the magnet.

• How can a material become a permanent magnet?

Its internal magnetic regions become aligned and stay aligned.

• What is a magnetic field?

The area around a magnet where magnetic forces can act.

• What do magnetic field lines show?

The direction and shape of a magnetic field.

• How does a compass work?

Its magnetic needle aligns with Earth's magnetic field.

• Why does Earth act like a giant magnet?

Earth produces its own magnetic field.

• What is magnetic declination?

The angle between geographic north and magnetic north.

• Why does a compass not always point toward true north?

Earth's magnetic north and geographic north are in different locations.

• What are superconductors?

Materials that have zero electrical resistance when in their superconducting state.

• What is the Meissner effect?

When a superconductor expels magnetic fields from its interior.

• Why can a magnet levitate above a superconductor?

Magnetic interactions caused by the Meissner effect can support the magnet.

• What is the main difference between electric charges and magnetic poles?

Electric charges can exist separately, but magnetic poles always come in north-south pairs.

8.2 Interactions Between Electricity and Magnetism

• What happens when an electric charge moves?

It creates a magnetic field.

• Does a stationary electric charge create a magnetic field?

No, a stationary charge does not create a magnetic field.

• What is electric current?

The movement of electric charges.

• What shape is the magnetic field around a straight current-carrying wire?

Circular loops around the wire.

• What happens to the magnetic field when electric current increases?

The magnetic field becomes stronger.

• What happens to the magnetic field as you move farther from a current-carrying wire?

The magnetic field becomes weaker.

• What happens when the direction of current is reversed?

The magnetic field reverses direction.

• What is an electromagnet?

A magnet created by electric current flowing through a coil of wire.

• What is the purpose of an iron core in an electromagnet?

It makes the magnetic field stronger.

• How can an electromagnet be made stronger?

Increase current, add more wire turns, or use an iron core.

• What is the advantage of an electromagnet over a permanent magnet?

It can be turned on and off by controlling the current.

• What is a solenoid?

A long coil of wire that creates a magnetic field when current flows through it.

• What happens when an iron rod is placed inside a solenoid?

It becomes magnetized and is pulled into the coil.

• What happens when the current in an electromagnet is reversed?

Its north and south poles switch.

• What happens to an electromagnet connected to AC?

Its magnetic field repeatedly changes direction.

• When can a magnetic field exert a force on an electric charge?

When the charge is moving.

• Does a magnetic field exert a magnetic force on a stationary electric charge?

No, the charge must be moving.

• In what direction does magnetic force act on a moving charge?

Perpendicular to both the charge's motion and the magnetic field.

• When does a moving charge experience no magnetic force?

When it moves parallel or opposite to the magnetic field.

• What happens to magnetic force when the current direction is reversed?

The direction of the force reverses.

• What is an electric motor?

A device that converts electrical energy into mechanical energy.

• How does an electric motor produce movement?

Magnetic forces act on a current-carrying coil and cause it to rotate.

• Why must the current reverse in an electric motor?

To keep the coil rotating in the same overall direction.

• What is electromagnetic induction?

Producing an electric voltage or current through a changing magnetic field.

• How can a magnet produce electricity in a coil?

Moving the magnet relative to the coil changes the magnetic field and induces voltage.

• Does the magnet or the coil have to move for induction to happen?

Either one can move; what matters is relative motion.

• What happens when a magnet moves back and forth through a coil?

The induced current repeatedly changes direction.

• What is an electric generator?

A device that converts mechanical energy into electrical energy.

• How does a generator produce electricity?

A rotating coil or magnet changes the magnetic field through a coil, inducing voltage.

• What is the difference between a motor and a generator?

A motor converts electricity into movement; a generator converts movement into electricity.

• What is regenerative braking?

A process that uses a vehicle's motor as a generator to recover energy during braking.

• Why is regenerative braking useful?

It converts some movement energy into electricity that can recharge the battery.

8.3 Principles of Electromagnetism

• How are electricity and magnetism connected?

Electric currents create magnetic fields, and changing magnetic fields can induce voltage.

• What is the main purpose of a transformer?

To increase or decrease AC voltage.

• What are the two coils in a transformer?

The primary coil (input) and secondary coil (output).

• How does a transformer work?

AC creates a changing magnetic field that induces voltage in the secondary coil.

• What determines the output voltage of a transformer?

The ratio of turns in the primary and secondary coils.

• What happens when the secondary coil has more turns than the primary coil?

Output voltage increases (step-up transformer).

• What happens when the secondary coil has fewer turns than the primary coil?

Output voltage decreases (step-down transformer).

• What happens when both transformer coils have equal turns?

Input and output voltages are equal.

• Why do transformers require AC?

AC creates a changing magnetic field that induces voltage in the secondary coil.

• Why doesn't steady DC work in a transformer?

DC produces a steady magnetic field that does not continuously induce voltage.

• What is a metal detector's basic principle?

Changing magnetic fields induce electric currents in nearby metal.

• How does a metal detector recognize metal?

The induced currents in the metal create magnetic fields that affect the detector.

8.4 Applications to Sound Reproduction

• What is a transducer?

A device that converts one form of energy into another.

• What does a microphone convert?

Sound energy into electrical energy.

• How does a microphone work?

Sound vibrates a diaphragm and coil, producing an electrical signal through induction.

• What happens when you speak into a microphone?

Sound waves vibrate the diaphragm, moving the coil and producing electricity.

• What does a speaker convert?

Electrical energy into sound energy.

• How does a speaker produce sound?

Electric current moves a coil, which vibrates the speaker cone and creates sound waves.

• What is the main difference between a microphone and a speaker?

A microphone converts sound into electricity; a speaker converts electricity into sound.

• What is magnetic tape made with?

A material containing tiny ferromagnetic particles.

• How is sound recorded onto magnetic tape?

An electromagnet changes the magnetization of particles on the tape.

• How does magnetic tape play back recorded sound?

Moving magnetic particles induce an electrical signal in a coil.

• What is the purpose of an amplifier?

To increase the power of a weak electrical signal.

• What is analog-to-digital conversion?

Changing an electrical sound signal into numerical information.

• How does digital recording store sound?

It measures sound waves and stores the measurements as binary numbers (0s and 1s).

• What is digital-to-analog conversion?

Changing digital numbers back into an electrical signal.

• Why is digital recording useful?

It allows sound to be stored and reproduced with less noise and imperfections.

8.5 Electromagnetic Waves

• What are electromagnetic waves?

Waves made of changing electric and magnetic fields.

• How are electromagnetic waves created?

Oscillating electric charges produce changing electric and magnetic fields.

• What is a transverse wave?

A wave in which the disturbance is perpendicular to the direction of travel.

• Do electromagnetic waves need a medium to travel?

No, they can travel through empty space.

• What is the speed of electromagnetic waves in a vacuum?

Approximately 300 million meters per second.

• What is the electromagnetic spectrum?

The complete range of electromagnetic waves organized by frequency and wavelength.

• What is the order of the electromagnetic spectrum from lowest to highest frequency?

Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray.

• What happens to wavelength when frequency increases?

Wavelength decreases.

• What happens to wavelength when frequency decreases?

Wavelength increases.

• What type of electromagnetic wave has the longest wavelength?

Radio waves.

• What type of electromagnetic wave has the shortest wavelength?

Gamma rays.

• What type of electromagnetic wave has the lowest frequency?

Radio waves.

• What type of electromagnetic wave has the highest frequency?

Gamma rays.

• What are radio waves commonly used for?

Radio, television, and wireless communication.

• How do radio antennas produce electromagnetic waves?

Alternating electric current causes charges to oscillate and produce electromagnetic waves.

• What are microwaves used for?

Cooking, Wi-Fi, Bluetooth, radar, and communication.

• How does a radar system detect objects?

It sends out microwaves and measures the waves that bounce back.

• How do microwave ovens heat food?

Changing electric fields interact with water molecules, increasing their motion and temperature.

• What are infrared waves commonly associated with?

Heat radiation.

• Why do warm objects emit infrared radiation?

Their atoms and molecules are moving and releasing electromagnetic radiation.