Comprehensive Physics: Waves, Sound, Electrostatics, Magnetism & Induction

Doppler Effect

Change in observed frequency due to motion of source or observer.

Pitch change when sound source moves toward you

Pitch (frequency) increases → sounds higher.

Pitch change when sound source moves away from you

Pitch (frequency) decreases → sounds lower.

Wave fronts in front of a moving sound source

They get compressed (shorter wavelength).

Common experiences of Doppler Effect

Ambulances, radar guns, astronomy.

What do waves transport?

Energy, not matter.

Transverse wave

Vibration is perpendicular to direction of travel (e.g. light, water wave).

Longitudinal wave

Vibration is parallel to direction of travel (e.g. sound in air).

Amplitude

Energy of the wave; higher amplitude = more energy.

Period

Time for one complete vibration or wave cycle.

Frequency

Number of vibrations per second (Hz).

Constructive interference

Waves combine to create a larger amplitude.

Destructive interference

Waves cancel out and reduce amplitude.

Technology using destructive interference

Noise-canceling headphones.

Standing waves

Waves trapped in a medium, forming nodes & antinodes (e.g. guitar strings).

Type of wave sound is

Mechanical, longitudinal pressure wave.

Can sound travel in a vacuum?

No — sound needs a medium.

State of matter sound travels fastest through

Solids, then liquids, then gases.

Effect of temperature on speed of sound in air

Warmer air → faster speed.

Ultrasonic

Frequencies above human hearing (> 20,000 Hz).

Infrasonic

Frequencies below human hearing (< 20 Hz).

Resonance

Matching natural frequency to increase vibration.

Particles that move to create electric charge

Electrons.

Opposite charges vs. like charges

Opposites attract, likes repel.

Charging by friction

Electrons transfer when two surfaces rub.

Charging by contact

Touch transfers charge.

Induction

Charging without touching, using repulsion/attraction of electrons.

Conductor

Material where electrons move freely (e.g. metals).

Insulator

Electrons do not move easily (e.g. rubber).

Charge polarization

The separation of charges within an object.

Electric current

Flow of electric charge (electrons).

Voltage

Electric potential energy per charge (push of electrons).

Resistance

Opposes flow of current.

Battery storage

No — voltage is stored; electrons already in circuit move.

Series circuit bulb failure

Entire circuit stops working.

Brightness in series circuit

More bulbs = more resistance = dimmer bulbs.

Parallel circuit voltage

Same voltage across each branch.

Independent operation of devices

Parallel circuits (like in a home).

Magnetic fields creation

Moving electric charges & electron spin.

Magnet poles

North & South — always paired, no monopoles.

Strength of magnetic fields

Where field lines are closest together (at poles).

Current direction and magnetic field

Thumb = current, fingers = direction of magnetic field loops.

Electromagnet strength factors

More current & more coil loops.

Magnetic alignment in iron

Magnetic domains.

Electromagnetic induction

Creating voltage by changing a magnetic field around a conductor.

Induced voltage with faster magnet movement

More induced voltage.

Loops in a coil and induced voltage

More loops in a coil means more induced voltage.

Generator purpose

Convert mechanical energy → electrical energy.

Transformers function

Change AC voltage levels.

High voltage power transmission

Reduces current → less heat loss in power lines.

Step-Up vs. Step-Down transformer

Step-Up: ↑ voltage, ↓ current; Step-Down: ↓ voltage, ↑ current.

Human hearing frequency range

20 Hz - 20,000 Hz.

Perception of higher frequency sounds

Higher pitch.

Compass near current-carrying wire

It deflects → showing magnetic fields around current.

Force attracting neutral soda can

Charge polarization.

Current creation in Faraday Lab

When magnetic field changes (moving magnet/coil).