Magnetism Review
Magnetic Field: The a
rea around a magnet or moving charge where magnetic forces can act.
Magnetic Domain: A tiny region in a material where electron spins line up in the same direction.
Permanent Magnet: A magnet where domains stay aligned on their own. - Example: Neodymium magnet.
Ferromagnetic Materials: Materials that easily become magnetic in an external field. - Example: Iron.
Paramagnetic Materials: Materials that are weakly affected by magnetic fields; domains do not strongly align. - Example: Aluminum.
Solenoid: A coil of wire that creates a strong magnetic field when current flows through it.
Magnetic Flux: The amount of magnetic field passing through an area.
Electromagnetic Induction: Voltage/current produced when magnetic flux changes through a wire loop.
Lenz’s Law: Induced current creates a magnetic field that opposes the change causing it. Used to find the direction of the induced current.
Photoelectric Effect: Electrons are emitted from a metal when light of high enough frequency hits it.
Photon: A particle (packet) of light energy.
Work Function: The minimum energy needed to remove electrons from a metal.
Quick Memory Tricks
Flux: Flow of magnetic field.
Induction: Creating current from changing magnetism.
Lenz’s Law: Opposes change.
Photon: Light particle.
Work Function: Energy requirement for electrons to escape.
Photoelectric Effect
Work function = minimum energy needed to remove an electron from a metal.
Photon energy depends on frequency.
E=hf
Important
Frequency below threshold → no electrons emitted
Higher frequency → electrons have more kinetic energy
Higher intensity (brightness) → more electrons emitted
Remember
Frequency affects energy
Brightness affects number of electrons
Electromagnetic Devices
Device | What Happens | Energy Conversion | Main Idea |
|---|---|---|---|
Speaker | Current causes cone to vibrate | Electrical → Sound | Moving charges create magnetic field |
Microphone | Sound vibrates coil, inducing current | Sound → Electrical | Electromagnetic induction |
Transformer | One coil induces current in another | Electrical → Electrical | Electromagnetic induction; uses AC only |
Motor | Current in magnetic field causes rotation | Electrical → Mechanical | Magnetic force on wire |
Generator | Rotating coil induces current | Mechanical → Electrical | Electromagnetic induction |
Solar Cell | Light ejects electrons | Light → Electrical | Photoelectric effect |
Quick Memory Tricks
Motor = electricity makes motion
Generator = motion makes electricity
Frequency = energy
Brightness = number of electrons
Most Likely Test Questions
What determines photon energy?
Frequency.
What is the work function?
Minimum energy needed to remove electrons.
What increases electron kinetic energy?
Increasing frequency.
What increases number of emitted electrons?
Increasing intensity/brightness.
Which use electromagnetic induction?
Microphone
Transformer
Generator
Which device only works with AC?
Transformer.