Download App

Alternating Current — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current3 Marks
Question
  1. When an AC source is connected to an ideal capacitor, show that the average power supplied by the source over a complete cycle is zero.
  2. A bulb is connected in series with a variable capacitor and an A.C. source as shown. What happens to the brightness of the bulb when the key is the capacitor is gradually reduced?

✓

Answer

  1. Let the applied voltage be

$\text{V}= \text{V}_{o}\sin\omega\text{t}$

The current through an ideal capacitor, would then be

$\text{I} = \text{I}_{o}\sin(\omega\text{t} + \frac{\pi}{2}) = \text{I}_{0}\cos\omega\text{t}$

$\therefore\text{P}_{inst} = \text{VI}$

$\therefore\text{P}_{AV} = \frac{1}{\text{T}}\int^{T}_{0}\text{VIdt}$

$\therefore\text{P}_{AV} = \frac{\text{V}_{0}\text{I}_{0}}{2}\langle\sin2\omega\text{t}\rangle$

$=0.$

  1. $\text{X}_{c} = \frac{1}{\omega\text{C}}$

$\therefore\text{X}_{c}$ increases as C decreases. Hence, with decreasing C, the brightness of the bulb would decrease.

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

More "3 Marks Question" from Alternating Current→Alternating Current — all question types→Physics STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

On the basis of Bohr's postulate obtain the formula for radius and total energy of electron in the $n^{\text {th }}$ stable orbit for hydrogen atom.
→
A transverse wave of amplitude 0.50mm and frequency 100Hz is produced on a wire stretched to a tension of 100N. If the wave speed is 100m/s, what average power is the source transmitting to the wire?
→
A capacitor is connected to an alternating-current source. Is there a magnetic field between the plates?
→
Obtain the equation of electric current for an AC circuit having only inductor.
→
A square plate of mass 120g and edge 5.0cm rotates about one of the edges. If it has a uniform angular acceleration of 0.2rad/s2, what torque acts on the plate?
→
A man has to go 50m due north, 40m due east and 20m due south to reach a field.
  1. What distance he has to walk to reach the field?
  2. What is his displacement from his house to the field?
→
Draw a schematic diagram of the experimental arrangement used by Davisson and Germer to establish the wave nature of electrons. Explain briefly how the de-Broglie relation was experimentally verified in case  of electrons.
→
The intensity of sound from a point source is 1.0 × 10-6W/m2 at a distance of 5.0m from the source. What will be the intensity at a distance of 25m from the source?
→
A neutron is absorbed by a $^{6}_{3}\text{Li}$ nucleus with the subsequent emission of an alpha particle.
  1. Calculate the energy released, in MeV, in this reaction.
  2. Write the corresponding nuclear reaction.
Given: mass $^{6}_{3}\text{Li} =6015126 $ u; mass (neutron) =1.0086654 u; mass (alpha particle) = 4.0026044 u and mass (triton) = 3.0100000 u. Take 1 u = 931 MeV/C2. 
→
The sunlight reaching Earth has maximum electric field of 810Vm-1. What is the maximum magnetic field in this light?
→