Questions 28-31: Two charged plates are connected to a power...

Questions 28-31: Two charged plates are connected to a power supply and have an intial charge of 2Q and energy density of 4µ: 28) If the area of the plates are doubled, the magnitude of charge on the plates become a) Q b) 2Q c) 4Q d) 0.5Q e) 8Q 29) If the distance between the plates are doubled, the magnitude of charge on the plates become a) Q b) 2Q c) 4Q d) 0.5Q e) 8Q 30) If a dielectric of constant K = 4 is added between the plates of the capacitor, the magnitude of charge on the plates become a) Q b) 2Q c) 4Q d) 0.5Q e) 8Q 31) If the voltage of the power supply is doubled, then the energy density of the capacitor becomes: a) ? b) 2? c) 4? d) 8? e) 16 ? 32) In which type of ideal material do electrons travel through freely without any loss of energy? a) insulators b) dielectrics c) conductors d) both a and b e) both band c

Transcript

00:01 In this question, we are looking at a parallel plate capacitor and i want to do some calculations on it.

00:09 So in part a, you want to draw an arrow indicating the direction of electric field between the plates.

00:15 So the electric field points from the positive to the negative.

00:20 So the e is pointing to the right.

00:24 And then in question 2a, you want to calculate the capacitance.

00:30 The plate dimension is 15 cm by 15 cm.

00:34 The gap is 1 .5 mm, and kappa is 1.

00:37 So we'll be using this formula.

00:41 So c equals to kappa, epsilon 0, a over d.

00:49 Kappa is 1, so i'm not writing it.

00:52 Epsilon is, epsilon 0 is 8 .85 times 10 to the negative 12.

00:57 And then the area is 15 cm square.

01:01 So convert to meter to be 0 .15 square.

01:05 Okay, the gap is 1 .5 m m.

01:09 And then you calculate this to be 1 .33 times 10 to the negative 10 ferret using our calculator.

01:21 And then in part 2b, we want to convert the answers into a to micro ferret and picofarret.

01:33 So c equals to 1 .5.

01:34 0 .33 times 10 to the negative 10 ferret it will be 10 to the 1 .33 times 10 to the negative 4 micro ferret is so equal to 1 3 times 10 1 3 pico ferret yeah so just the other micro is sent to the negative 6 so just imagine you can break like the 10 to the negative 10 to somewhere just pull 10 to the negative 6 out and what's remaining we tend to the negative fall and then you can change it to micro ferret okay yeah same same thing for picofarret okay so when d decreases okay number three when d decreases the c would increase okay so yeah because c is inversely proportional to d key number four um if you charge the capacitor with a 24 battery was the electrical potential energy so we'll be using this formula you equals to half cb square okay so half times 1 .33 times 10 to the negative 10 times 24 square okay you get 3 .82 times 10 to the negative 8 juice.

03:16 Okay, so this is the answer for question 4 then 4b.

03:22 If we disconnect the battery and move the plates to a separation of 0 .1 m m.

03:29 Okay meaning the d becomes smaller.

03:32 That's the charge change and says no because the battery is disconnected.

03:37 Okay, yeah no charge can flow to the plates.

03:42 So the charge on the capacitor will not change.

03:46 And then for c we need to calculate a new voltage and the energy start in the capacitor.

03:52 So we will calculate the c new first...

Question

Please give Ace some feedback