Circuits, Magnetism, Waves, and Sound

Parallel Resistors

-Same voltage, each get same voltage

-What current goes in must come out, I1=I2+I3 if R2=R3 then I2=I3

Series Resistors

-Each get part of voltage, add up to voltage of battery

-Different voltage, different R

-Same current

Important equation

V=IR

Power

P=IV=I²R=V²/R

Power output by battery: electrical energy

Power dissipated across resistors: thermal energy

Least power, smallest current, then smallest R

Magnetic fields and force equation

FB=qVBSin(theta)

Right hand rule criteria

Before during RHR:

Fb cannot be equal to 0

q>0, v>0, sin theta cannot be 0 or 180 degrees

Right hand rule

Thumb=V or current

Pointer=B or magnetic field

Middle=Force

“Very Beautiful Friends”

Left hand for negative charges!

Magnetic field

All charges move in circular motion

Magnetic field does no work, work is always = 0

Movement

Straight line just electrical field (+ to -)

Cycloid-both or some weird shape

Circular-B only

Other right hand rule

Thumb current, curl hands direction of magnetic field

Out of page vs into page

Out of page vs into page

Harmonic motion

F=-kx mass on a spring

F proportional to d

PE=1/2kx² PE most at +-A max!

Wspring=-deltaPEelastic

KEi+PEi=KEf+PEf

Period and frequency

f=1/T

Transverse waves

Moving up and down

Waves on a string, electromagnetic waves

Longitudinal waves

Parallel

Sound waves

Equation

V=lambda(f)

Speed wave in medium

Depends on physical properties of wave

Speed constant in medium

Wave moving from one medium to another

f constant between mediums!!!

Numbers to know about waves

Speed of light in vacuum: 3 × 10^8 m/s

Speed of sounds in air: 350 m/s

Speed of sounds in water: 1500 m/s

Standing waves

Fn=nf

lambda=2L/n

Open-open both nodes

Closed-closed both end antinodes

All points on the string between any two adjacent nodes vibrate together—in phase—so the period of oscillation is independent of position.

Sound

I=power/area

Same as energy

I is proportional to 1/r²

I is proportional A²

Intensity/sound level

B=10log10(I/Io)

Io=10^-12

B in dB

***For every increase in I by factor of 10 add 10 to B, decrease subtract 10 from B

Example with sound intensity equation

Io=10

I=1000

1000/10=100/1 or 10²/10^0 = 2 factors of 10 gained so +20

-Decreases by 90 % so 10 % remaining 10/100 10^1/10² 1/10 so loss of 10 dB

-Increases factor of 30

10 +10 100 +20 1000 +30 so in between +10 and +20

Doppler shift

Moving source: V=lambda* f. Lambda decrease, f increases.

Moving observer: V=lambda * f. V increase, f increases.

Closer together, higher frequency

Doppler shift

fd=fs(V+-Vd/V-+Vs)

Use Top sign for Towards. Bottom sign-away.

D=detector

V+-Vd perspective of detector, detector moving away for example so -

V+-Vs perspective of source, source moving towards detector so -