Download App

Capacitors — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsCapacitors5 Marks
Question
A parallel-plate capacitor has plate area $25.0cm^2$ and a separation of 2.00mm between the plates. The capacitor is connected to a battery of 12.0V:
  1. Find the charge on the capacitor.
  2. The plate separation is decreased to 1.00mm. Find the extra charge given by the battery to the positive plate.
✓

Answer



Plate area $A = 25cm^2 = 2.5 \times 10^{-3}m$
Separation $d = 2mm = 2 \times 10^{-3}m$
Potential $v = 12v$​​​​​​​
  1. We know
$\text{C}=\frac{\in_0\text{A}}{\text{d}}$
$=\frac{8.85\times10^{-12}\times2.5\times10^{-3}}{2\times10^{-3}}$
$=11.06\times10^{-12}\text{F}$
$\text{C}=\frac{\text{q}}{\text{v}}$
$\Rightarrow11.06\times10^{-12}=\frac{\text{q}}{12}$
$\Rightarrow\text{q}_1=1.32\times10^{-10}\text{C}.$
  1. Then d = decreased to 1mm
$\therefore\ \text{d}=1\text{mm}=1\times10^{-3}\text{m}$
$\text{C}=\frac{\in_0\text{A}}{\text{d}}=\frac{\text{q}}{\text{v}}$
$=\frac{8.85\times10^{-12}\times2.5\times10^{-3}}{1\times10^{-3}}=\frac{2}{12}$
$\Rightarrow\text{q}_2=8.85\times2.5\times12\times10^{-12}$
$\Rightarrow\text{q}_2=2.65\times10^{-10}\text{C}.$
$\therefore$ The extra charge given to plate $= (2.65 - 1.32) \times 10^{-10} = 1.33 \times 10^{-10}C.$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

Physics STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

Answer the following questions:
(a) Are the equations of nuclear reactions (such as those given in Section 13.7) 'balanced' in the sense a chemical equation (e.g., $2 H _2+ O _2 \rightarrow 2 H _2 O$ ) is? If not, in what sense are they balanced on both sides?
(b) If both the number of protons and the number of neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice-versa) in a nuclear reaction?
(c) A general impression exists that mass-energy interconversion takes place only in nuclear reaction and never in chemical reaction. This is strictly speaking, incorrect. Explain.
→
A vessel of volume $125cm^3$ contains tritium $\big(\text{ }^3\text{H,t}_{\frac{1}{2}}=12.3\text{y}\big)$ at 500 kPa and 300K. Calculate the activity of the gas.
→
A particle on a stretched string supporting a travelling wave, takes 5.0ms to move from its mean position to the extreme position. The distance between two consecutive particles, which are at their mean positions, is 2.0cm. Find the frequency, the wavelength and the wave speed.
→
4.0g of helium occupies $22400cm^3$ at STP. The specific heat capacity of helium at constant pressure is $5.0cal-K^{-1}mol^{-1}.$ Calculate the speed of sound in helium at STP.
→
Explain ac voltage applied on a capacitor.Explain charging and discharging of a capacitor.
→
An X-ray tube operates at 40kV. Suppose the electron converts 70% of its energy into a photon at each collision. Find the lowest there wavelengths emitted from the tube. Neglect the energy imparted to the atom with which the electron collides.
→
Consider the D–T reaction (deuterium–tritium fusion)
$^2_1\text{H}+^3_1\text{H}\rightarrow^4_2\text{He}+\text{n} $
  1. Calculate the energy released in MeV in this reaction from the data:
$\text{m}(^2_1\text{H})=2.014102\text{ u}$
$\text{m}(^3_1\text{H})=3.016049\text{ u}$
  1. Consider the radius of both deuterium and tritium to be approximately 2.0 fm. What is the kinetic energy needed to overcome the coulomb repulsion between the two nuclei? To what temperature must the gas be heated to initiate the reaction? (Hint: Kinetic energy required for one fusion event =average thermal kinetic energy available with the interacting particles = 2(3kT/2); k = Boltzman’s constant, T = absolute temperature.)
→
A circular loop carrying a current i is made of a wire of length L. A uniform magnetic field B exists parallel to the plane of the loop.
  1. Find the torque on the loop.
  2. If the same length of the wire is used to form a square loop, what would be the torque? Which is larger?
→
Find the maximum magnitude of the linear momentum of a photoelectron emitted when light of wavelength 400 run falls on a metal having work function 2.5eV.
→
Do the same exercise as above with the replacement of the earlier transformer by a 40, 000-220V step-down transformer (Neglect, as before, leakage losses though this may not be a good assumption any longer because of the very high voltage transmission involved). Hence, explain why high voltage transmission is preferred?
→