Download AP Physics things to remember

Mr Frye’s stream of consciousness AP Physics things to remember – read the following and cognitively engage
the information to see if you understand the concepts and remember the relationships
Mechanics
Centripetal acceleration is proportional to v2, inversely proportional to r (radius).
Kinetic energy of anything that has mass is proportional to v2 .
Energy of a photon is hf – nothing but a ripple in a mag/E field goes the speed of light- ie. photons whose rest mass is zero.
Work is the transfer of energy where the force is in the direction of, (parallel to) the distance it is pushed through.
Force in a spring is proportional to the distance moved.
Total energy in a system (spring mass, rollercoaster, pendulum….) absent of non-conservative forces is constant. PE goes to
KE and vice versa..
Period of a pendulum is prop to sqrt of its length, and inversely prop to the sqrt of the local acceleration of gravity.
Would the same pendulum swing faster or slower on the moon?
Period of a spring mass system is prop to sqrt of mass, and inversely prop to the sqrt of the k .
Would the same spring mass system oscillate faster or slower on the moon?
Force of Gravity is prop to the masses inversely prop to the SQUARE of the distances.
In describing motion always comment on the object’s acceleration and velocity.
FBDs - only draw the individual forces NOT their components.
E&M
Capacitance is dependent on the physical geometry of the capacitor – changing the voltage changes the charge on it not the
capacitance…..
Capacitance is prop to Area of plates and inversely prop to separation distance.
Increasing the voltage on a Capacitor is like increasing the pressure on a balloon – you squeeze more charge into it Q=CV.
Resistance is dependent (for most resistors that are ohmic) on the actual physical object. Typically the resistance does not
change if a different voltage is placed across it. Resistance is prop to length and inversely to cross sectional area.
V=kq/r is potential at a distance from a POINT charge! NOT for UNIFORM Fields. Voltage is NOT A Vector it is energy/q.
E = kq/r2 is for a POINT charge! Not for a uniform electric field. E field is a VECTOR.
A uniform Electric Field is where the field lines are parallel and the voltage (Potential energy per charge) changes with
distance ΔV= -EΔx
Induced EMF(electromotive force/ voltage) is proportional to the rate of change in mag flux (BAcosθ)
EMF = Δ BAcosθ/Δt
Force due to an Efield is F= Eq and it is a VECTOR, E is a vector toooooo. The force points along the direction of the field.
NOT SO with Mag Field – USE I – flow of positive charge , B- mag field direction(points from north to south) , F- force
direction (thumb, pointer, middle) to find direction of force on a moving charge, which is perpendicular to its motion causing
circular paths and centripetal accelereation.
For Capacitors in series the charge is the same on each and the capacitor equivalent is the 1/C thingy, in parallel the voltage is
the same and the equivalent capacitance just adds up, like just making a larger plate…..
Resistors in series the current is the same and the equivalent resistance just adds up ( more obstacles for the e to travel
through), in parallel the voltage is the same and the equivalent resistance is the 1/R thingy.
Kirchoff loop – the voltages around a loop add up to zero – this is CONSERVATION of _________
Kirchoff junct – the currents in and out of a junct add up to zero – this is CONSERVATION of ___________
Brightness (or intensity which is P/A like watts per square meter) of a bulb is determined by its power output
Thermo and Fluids
Bernoulli is a CONSERVATION of ________________ equation.
Actual/Absolute pressure is gage plus atmospheric – The gage pressure in the room is 0psi, the absolute pressure is about
14.7psi
Continuity is Conservation of Mass and volume for an incompressible fluid A1v1= A2v2
Heat flow through a material is prop to Cross sectional area, & ΔTemp and inversely prop to length.
Kinetic energy and therefore the internal energy(because in an ideal gas there is no potential energy interaction between the
particles) of an ideal gas is proportional to the Temperature of the gas. So for an ideal gas the internal energy of the gas is a
STATE FUNCTION (independent of path) and solely dependant on its TEMPERATURE: U = 3/2nRT, K ave of a molecule in gas
=3/2kbT
The vrms is then proportional to the sqrt of temperature, just like the v is prop to sqrt of kinetic energy….
2moles of Helium and 2moles of oxygen are at the same temp. Which one has the higher U?
Which one has the higer vrms ??????
The work done on a gas and the heat added to a gas are PATH functions. Work is area under PV curve – going from left to
right is work done by gas which in AP is negative W. The Q can be figured from the ΔU(ΔT) and W(PΔV)
Thermo and Fluids continued
What is going on in a gas where at constant pressure the volume is increasing?hmmm?
Efficiency is what we get out over what we put in so e = Workoutput/Q h = (Th – Tc)/Th
As a piece of material heats up, the change in linear dimensions increase prop to original length and ΔT.
As you heat up a piece of material with a hole in it, the hole gets (smaller, bigger)
Waves and Optics
FREQENCY stays the SAME! (unless of course we are talking about a Doppler shift……)
Index of refraction is the factor by which the velocity and wavelength of light is REDUCED n=c/v = λ0/λ when it enters that
medium.
For the following think of the mirror and lens equation 1/d i + 1/do = 1/f
The focal length for converging optics is positive (concave mirror, convex lens)
The focal length for diverging optics is negative(convex mirror, concave lens)
The focal length for the spherical mirrors we study is half the radius of curvature of the mirror.
Remember how to trace the 7 cases.
Positive image distance means it is a real image
Negative image distance means it is virtual
For the real objects we study(meaning do positive) – vitual images(di neg) will be upright (magnification positive)
For the real objects we study(meaning do positive) - real images(di positive) will be inverted (magnification negative)
For diffraction patterns the angle to the max and mins gets smaller as the grating spacing gets bigger(d bigger=less lines per
length) and the angle gets smaller the smaller the wavelength.
The visible spectrum is from ____________nm (violet) to __________nm (red)
The d sin(theta)= m(lambda) equation can be used for sound interference problems where the distance to the listener is a few
times further in distance than the distance between the two sources.
Atom and Photons and Energy
Energy of photon is hf, but you knew that. Photon model of EMR explains ______ ________ radiation
The momentum of a photon is hf/c not mv cause it gots no mass!
Energy is conserved
Increasing the intensity of a beam of light can be done in two ways ____________ and __________
Compton Shift both momentum and K are conserved in a collision of a photon and electron.
If EMR is shining on a surface but there is not enough energy to knock electrons out because the work function has not been
met then can we just increase the intensity of the beam???
Energy jumps by electrons around an atom’s energy levels are all about energy. If an electron jumps from a level at -3eV to a
level that is -8eV, a ___________ will be released with an energy of _____________, and of frequency______________.
To get the deBroglie wavelength of a particle you must know its____________
Three types of ionizing radiation:
1.
2.
3.
An atom has a neutron release a __________ particle and the atomic number went up. What happened to the atom?
Thompson Plumb Pudding – discovered e-, Miliken oil drop measured the charge on it
Geiger and Marsden Tested Thompsons atom by shooting beta source at Gold foil – but beta particles went straight
through?!?!?!?!?!
Rutherford said look for steeper angles of deflection – some beta particles came right back?!?explanation ___________.
Bohr orbits
deBroglie waves fit at certain intervals around the atom and fit the Bohr orbits for quantized energy levels – he also said maybe
particles are waves…Davison and Germer proved it with diffraction of electrons.