PHSC 101: Electricity, Magnetism, Waves, and Light Key Concepts

Electric Charge

Two types of charge: positive (+) and negative (-).

Coulomb's Law

Describes how the force between two charges depends on their magnitude and distance: F=k * q1q2/ d2.

Electric Field

Space around a charge where other charges feel a force.

Electric Potential

Potential energy per unit charge, measured in volts (V).

Electric Current

Flow of electric charge (electrons), measured in amperes (A).

Resistance

Opposition to current flow, measured in ohms (Ω).

Ohm's Law

V=I * R; the voltage across a resistor equals the current times the resistance.

Power in Circuits

P=I * V = I^2 R = V^2/ R; power is the rate energy is converted.

Series Circuits

Same current through all components; voltage splits.

Parallel Circuits

Same voltage across all components; current splits.

Magnetic Fields

Created by moving charges or currents; field lines go from north to south outside a magnet.

Magnetic Force

Moving charges feel a force in a magnetic field: F=qvBsin⁡θ.

Electromagnetic Induction

Changing magnetic fields can induce electric currents (Faraday's Law).

Induced Voltage

V induced = N * ΔB/Δt; faster change results in stronger induced voltage.

Lenz's Law

The direction of induced current opposes the change.

Charge Conservation

Charge is conserved; it cannot be created or destroyed, only transferred.

Electric Forces

Extremely strong compared to gravity; act through fields, not by direct contact.

Field Lines

Show direction of force on a positive test charge; never cross.

Voltage Difference

Difference in electric potential, what makes current flow.

Current Splitting in Parallel

Current splits according to 1/Req=1/R1+1/R2+… in parallel circuits.

Action at a Distance

Charges exert forces without touching because they produce an electric field around them.

Transformer

Used to change voltage up or down.

Vp/Vs=Np/Ns

Vp: primary voltage, Vs: secondary voltage; Np: primary coil turns, Ns: secondary coil turns.

Step-up transformer

Increases voltage (fewer turns → more turns).

Step-down transformer

Decreases voltage (more turns → fewer turns).

AC current

Works only with AC current (changing magnetic fields needed).

Waves

Waves transfer energy, not matter.

Transverse wave

Vibration ⟂ direction (light, EM waves).

Longitudinal wave

Vibration ∥ direction (sound).

Wave speed formula

Speed = frequency × wavelength.

Reflection

Bouncing off a surface (angle in = angle out).

Refraction

Bending as it enters a new medium due to speed change.

Doppler Effect

The apparent change in frequency when a source or observer moves.

Higher pitch/frequency

Occurs when moving toward the source.

Lower pitch/frequency

Occurs when moving away from the source.

Light as a wave

Light is an electromagnetic wave (doesn't need a medium).

Speed of light

Speed of light in vacuum: 3.0 × 10⁸ m/s.

Plane mirrors

Reflect light, image same size, reversed left-right.

Concave mirrors

Converge light (focus).

Convex mirrors

Diverge light (wider view).

Snell's Law

n1sin⁡θ1=n2sin⁡θ2.

Index of refraction (n)

How much light slows in a material.

Convex lenses

Focus light (used in magnifiers, eyes).

Concave lenses

Spread light out (used in glasses for nearsightedness).

White light

Mix of all colors (ROYGBIV).

Color dependence

Depends on wavelength and what the object reflects or absorbs.

Dispersion

Separation of light into colors due to different refraction for each wavelength (rainbows, prisms).

Polarization

Light waves vibrating in one direction only; happens only for transverse waves.