# AP Physics 2: 1.4 Changes and Conservation Laws

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AP Physics 2: 1.4 Changes and Conservation Laws. Find the capacitance of the capacitor.

AP | AP Physics 2 |

AP Physics 2 | Changes and Conservation Laws |

Language | English Language |

Test Prep | AP Physics 2 |

### Transcript

battery on his camera phone is dead he rushes up to the attic finds an old

flashbulb camera and makes it back down just in time to snap a photo of the [Chris using flashbulb camera]

Admiral the energy used to produce the flash is stored in a capacitor the flash

pulse has the power of 100 thousand watts and a duration of .001

seconds and the potential difference be across the capacitor plates is held

constant at 200 volts, energy is stored in a capacitor with a capacitance of C at a [physics formula]

potential difference V determine the capacitance of the capacitor assume all

the energy stored in the capacitor is converted into energy for the flash and

here are the potential answers..different kind of flash... All right, [potential answers and the Flash appears]

look not to sound jaded but we've seen all the pictures of cats playing the

piano the internet is built on piano playing cat pics is any image search [internet page of cats playing piano]

will prove sorry Chris but without video evidence of the Admiral playing

Beethoven's ninth were not impressed but a flashbulb camera that we are impressed [Chris takes picture of girl with flashbulb camera]

with it's like a historical artifact from a simpler time okay, enough about

cats and cameras.. in order to solve this problem we first need to find out how [two hands with sparks in between]

much power we're dealing with. Since all the energy in the capacitor is used by

the flash if we can figure out how much energy is needed to blind poor Admiral [Admiral being photographed by Chris]

Snugglesworth then we can figure out the total energy we're dealing with well

energy equals power times time in this case we have a hundred thousand watts of [Energy formula shown on blackboard]

power used in one, one thousandth of a second and that means the total energy

is a hundred joules we were already given the equation to calculate the

stored energy we just need to arrange that equation to find the capacitance [equation for stored energy rearranged]

starting with the equation U sub E equals one half CV squared we find that

C equals 2U sub E over V squared plugging in the numbers we find that the

capacitance equals five microfarads which means the correct answer is D

if we ever have a pet talented enough to actually play an instrument we're going [Admiral playing the piano and jumps on Chris]

to be very careful taking pictures the last thing we want from her is to get

camera shy because we finally get the paparazzi's attention we've always [paparazzi taking snaps of Admiral and Chris]

wanted.