Advertisements
Advertisements
प्रश्न
Why does current in a steady state not flow in a capacitor connected across a battery? However momentary current does flow during charging or discharging of the capacitor. Explain.
Advertisements
उत्तर
In steady state condition, voltage across the capacitor nearly equals to the voltage of the charging source. Hence net voltage acting in the circuit is zero. Due to this there is no flow of charge (current) through the circuit and hence the capacitor.
Now we know for an uncharged capacitor the potential difference across the capacitor is zero. So when it is connected to a battery, the battery begins to charge it by withdrawing the free electrons from one plate connected with the positive terminal of the battery of the capacitance and deposit on the other plate of the capacitor. So, due to this flow of charge, there exist a momentary current while charging of the capacitor. Now when the capacitor is fully charged i.e. voltage across the capacitor nearly equals to the voltage of the charging source, the current in the circuit vanishes.
Now in case of discharging of a charged capacitor, the battery gets replaced by a wire of say resistance R. Hence the capacitor itself acts as a battery now and flow of charge exists in the circuit from negative plate to the positive plate of the battery. This leads to momentary current in the circuit. As soon as the all the positive charges on one plate gets neutralised by the negative charges on the other plate, the flow of charge stops and hence the current.
APPEARS IN
संबंधित प्रश्न
Define 'quality factor' of resonance in a series LCR circuit. What is its SI unit?
The time constant of an LR circuit is 40 ms. The circuit is connected at t = 0 and the steady-state current is found to be 2.0 A. Find the current at (a) t = 10 ms (b) t = 20 ms, (c) t = 100 ms and (d) t = 1 s.
An inductor-coil of inductance 17 mH is constructed from a copper wire of length 100 m and cross-sectional area 1 mm2. Calculate the time constant of the circuit if this inductor is joined across an ideal battery. The resistivity of copper = 1.7 × 10−8 Ω-m.
An inductor of inductance 2.00 H is joined in series with a resistor of resistance 200 Ω and a battery of emf 2.00 V. At t = 10 ms, find (a) the current in the circuit, (b) the power delivered by the battery, (c) the power dissipated in heating the resistor and (d) the rate at which energy is being stored in magnetic field.
Obtain the resonant frequency and Q-factor of a series LCR circuit with L = 3.0 H, C = 27 µF, and R = 7.4 Ω. It is desired to improve the sharpness of the resonance of the circuit by reducing its ‘full width at half maximum’ by a factor of 2. Suggest a suitable way.
A series LCR circuit contains inductance 5 mH, capacitance 2µF and resistance ion. If a frequency A.C. source is varied, what is the frequency at which maximum power is dissipated?
A coil of 0.01 henry inductance and 1 ohm resistance is connected to 200 volt, 50 Hz ac supply. Find the impedance of the circuit and time lag between max. alternating voltage and current.
For an LCR circuit driven at frequency ω, the equation reads
`L (di)/(dt) + Ri + q/C = v_i = v_m` sin ωt
- Multiply the equation by i and simplify where possible.
- Interpret each term physically.
- Cast the equation in the form of a conservation of energy statement.
- Integrate the equation over one cycle to find that the phase difference between v and i must be acute.
Select the most appropriate option with regard to resonance in a series LCR circuit.
Three students, X, Y and Z performed an experiment for studying the variation of ac with frequency in a series LCR circuit and obtained the graphs as shown below. They all used
- an AC source of the same emf and
- inductance of the same value.
- Who used minimum resistance?
- In which case will the quality Q factor be maximum?
- What did the students conclude about the nature of impedance at resonant frequency (f0)?
- An ideal capacitor is connected across 220 V, 50 Hz, and 220 V, 100 Hz supplies. Find the ratio of current flowing through it in the two cases.
