physics exam 2 notes

gravitational force

masses attracting other masses

strong force

binds nucleons

weak force

governs beta decay

electromagnetism

• physics of electrical charge

• includes physics of electricity and magnetism

electrons

• fundamental particles

• are leptons

• -1.6 × 10^-19 C

protons

• not fundamental particles

• are hadrons

• 1.6 x 10^-19 C

charge

1C= 1A x 1S

amp

1A= 1C / 1S

conductor

transfers electricity efficiently

insulator

transfers electricity inefficiently

semi-conductor

sometimes a conductor and sometimes an insulator, depending on the electrical input

superconductor

has little to no resistance to electricity

induction

transfer of charge

transistor

an electrical component, has 3 legs, made of semi-conductor material, controls input and output of electrical signals

capacitator

holds charge between two insulators, stores electric potential energy

circuit

a complete closed path that allows electric charge to flow (electric current)

potential difference

potential difference between two points on a circuit is the work done to move a charge from one point to another

units for potential

Nm/C = J/C = energy/charge = Kq/r

potential

energy per charge

Ohm’s law

V= IR

series circuit

a single path for the electrical current

parallel circuit

• many separate pathways exist for the electrical current

• voltage is the same across each branch

• current is calculated for each branch based on its resistance and the sum of each branch gives the output current which is always the same as the input current

direct current

the flow of electric current in one direction

alternating current

the flow of electric current in both directions

diodee

an electric component that only allows the flow of electric current in one direction

resistor

an electric component that resists electrical current. measured in Ω

how to measure resistance in a series circuit

add them. answer will always be a positive number

how to measure resistance in a parallel circuit

I/?Ω= (1/B1 + 1/B2 + 1/B3…)

watts

unit for power. power= current x potential (W=IV)

electric field

N/C= force per charge. V/M= potential per distance. has electric field lines, which are the path the electric field takes. field lines show direction btwn positive and negative charges, going from positive to negative. field lines follow the path of the circuit

orbital electron angular momentum

• the angular momentum associated with an electrons motion in its atomic orbital

• creates an orbital magnetic moment (a tiny current loop)

• distinct from intrinsic angular momentum

intrinsic electron spin

• a fundamental form of angular momentum

• electron possesses it

• bc the electron is charged, spin gives a magnetic moment, making spin behave like tiny bar magnets

• two orientations: spin up and spin down

Stern-Gerlach experiment

demonstrated that electrons have spin

magnetism

microscopic magnetic moments from electrons: such as spin and sometimes orbital motion

magnetic domain

• a region inside a magnetic material where a vast number of atomic magnetic moments are aligned in

• neighboring domains can point different ways and overall magnetization is the vector sum

• applying a magnetic field grows domains aligned w/ the field and shrinks or flips others

magnetic field

• a field produced by moving charges (current)

• unit for magnetic field is T (tesla)

• field lines form closed loops

• magnetic fields exert forces on magnetic moments and on moving charges

magnetic force

• its direction is dictated by the right hand rule

• zero if motion is parallel to the magnetic field, maximal if perpendicular

• follows an inverse square law

electromagnet

• a magnet made by running a current through a coil

• strength of the electromagnet depends on 3 main things: number of turns in the coil, the current through the coil, and the coil’s material

• advantages: switchable and controllable

Faraday’s law

a changing magnetic field through a loop induces voltage in that loop

Maxwell’s counterpart to Faraday’s law

the inverse holds true. magnetic fields curl around currents and around changing electric fields

electric motor

• device that converts electrical energy into mechanical energy

• a current is applied to a coil which moves a magnet

electric generator

• device that converts mechanical energy intro electrical energy

• rotating a coil in a magnetic field changes the magnetic field through the coil, inducing voltage into the coil

transformer

• an electrical component that uses mutual induction to step voltage up or down btwn two coils

• operates with an alternating current

• power in= power out

• Vp/Vs= Np/Ns