Home
Class 12
PHYSICS
A capacitor of capacitance C charged by...

A capacitor of capacitance C charged by battery at V volt and then disconnected. At t = 0, it is connected to an uncharged capacitor of capacitance 2C through a resistance R. The charge on the second capacitor as a function of time is given by `q=(alpha CV)/(3) (1-e^(-(3t)/(beta RC)))` then fing the value of `(alpha )/(beta)`.

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the situation involving the two capacitors and the resistor. Let's break it down step by step. ### Step 1: Understand the Initial Conditions We have a capacitor of capacitance \( C \) charged to a voltage \( V \). The charge on this capacitor when fully charged is given by: \[ Q_0 = C \cdot V \] At \( t = 0 \), this charged capacitor is disconnected from the battery and connected to an uncharged capacitor of capacitance \( 2C \) through a resistor \( R \). **Hint:** Remember that the initial charge on the first capacitor is \( Q_0 = C \cdot V \). ### Step 2: Set Up the Charge Conservation Equation When the charged capacitor \( C \) is connected to the uncharged capacitor \( 2C \), charge will redistribute between them. Let \( q \) be the charge on the \( 2C \) capacitor at time \( t \). The charge on the \( C \) capacitor will then be \( Q_0 - q \). Using Kirchhoff's law, we can write the equation for the charge: \[ \frac{Q_0 - q}{C} + \frac{q}{2C} = 0 \] This simplifies to: \[ \frac{Q_0 - q}{C} = -\frac{q}{2C} \] **Hint:** Use Kirchhoff's voltage law to set up the equation based on charge conservation. ### Step 3: Rearranging the Equation From the equation above, we can rearrange it to find a relationship between \( q \) and \( Q_0 \): \[ Q_0 - q = -\frac{q}{2} \] Multiplying through by \( 2C \) gives: \[ 2C(Q_0 - q) = -q \] Expanding this, we have: \[ 2CQ_0 - 2Cq = -q \] Rearranging leads to: \[ 2CQ_0 = 2Cq - q \implies 2CQ_0 = q(2C + 1) \] Thus, \[ q = \frac{2CQ_0}{2C + 1} \] **Hint:** Rearranging the charge conservation equation helps in isolating \( q \). ### Step 4: Deriving the Differential Equation The current \( I \) flowing through the resistor can be expressed as: \[ I = -\frac{dq}{dt} \] Using Ohm's law, we have: \[ I = \frac{Q_0 - q}{R} \] Setting these equal gives: \[ -\frac{dq}{dt} = \frac{Q_0 - q}{R} \] **Hint:** Relate the current to the change in charge over time. ### Step 5: Solve the Differential Equation Rearranging gives: \[ \frac{dq}{Q_0 - q} = -\frac{dt}{R} \] Integrating both sides: \[ -\ln|Q_0 - q| = \frac{t}{R} + C \] Exponentiating leads to: \[ Q_0 - q = K e^{-\frac{t}{R}} \] where \( K \) is a constant determined by initial conditions. **Hint:** Use integration to solve the differential equation. ### Step 6: Apply Initial Conditions At \( t = 0 \), \( q = 0 \): \[ Q_0 - 0 = K e^{0} \implies K = Q_0 \] Thus, we have: \[ Q_0 - q = Q_0 e^{-\frac{t}{R}} \implies q = Q_0(1 - e^{-\frac{t}{R}}) \] **Hint:** Use the initial condition to find the constant \( K \). ### Step 7: Relate to Given Function The problem states that: \[ q = \frac{\alpha CV}{3} (1 - e^{-\frac{3t}{\beta RC}}) \] Comparing this with our derived equation: \[ q = Q_0(1 - e^{-\frac{t}{R}}) \] We see that: \[ Q_0 = CV \implies \frac{\alpha CV}{3} = CV \implies \alpha = 3 \] And from the exponent: \[ -\frac{t}{R} = -\frac{3t}{\beta RC} \implies \beta = 3 \] ### Step 8: Find \( \frac{\alpha}{\beta} \) Now we can find: \[ \frac{\alpha}{\beta} = \frac{3}{3} = 1 \] ### Final Answer Thus, the value of \( \frac{\alpha}{\beta} \) is: \[ \boxed{1} \]
Promotional Banner

Topper's Solved these Questions

  • CAPACITANCE

    RESONANCE|Exercise Exercise - 3|26 Videos
  • CAPACITANCE

    RESONANCE|Exercise High Level Problems|16 Videos
  • CAPACITANCE

    RESONANCE|Exercise Exercise - 1|79 Videos
  • ATOMIC PHYSICS

    RESONANCE|Exercise Advanved level problems|17 Videos
  • COMMUNICATION SYSTEMS

    RESONANCE|Exercise Exercise 3|13 Videos

Similar Questions

Explore conceptually related problems

A capacitor of capacitance C is given a charge Q. At t=0 ,it is connected to an uncharged of equal capacitance through a resistance R. Find the charge on the second capacitor as a function of time.

A capacitor of capacitance C is given a charge go. At time t = 0 it is connected to an uncharged capacitor of equal capacitance through a resistance R . Find the charge on the first capacitor and the second capacitor as a function of time t . Also plot the corresponding q-t graphs.

A capacitor of capacitance C_0 is charged to potential V_0 . Now it is connected to another uncharged capacitor of capacitance C_0/2 . Calculate the heat loss in this process.

A capacitor of capacitance C_(1) is charged to a potential difference V and then connected with an uncharged capacitor of capacitance C_(2) a resistance R. The switch is closed at t = 0. Choose the correct option(s):

A capacitor of capacitance C is given a charge go. At time t = 0 , it is connected to a battery of emf E through a resistance R . Find the charge on the capacitor at time t .

A 80muF capacitor is charged by a 50V battery. The capacitor is disconnected from the battery and then connected across another uncharged 320muF capacitor. Calculate the charge on the second capacitor.

A capacitor of capacitance as C is given a charge Q. At t=0 ,it is connected to an ideal battery of emf (epsilon) through a resistance R. Find the charge on the capacitor at time t.

A capacitor or capacitance C_(1) is charge to a potential V and then connected in parallel to an uncharged capacitor of capacitance C_(2) . The fianl potential difference across each capacitor will be

A capacitor of capacity 20microF is charged upto 50V and and disconnected from cell. Now this charged capacitor is connected to another capacitor of capacitance C If final common potential is 20V then find the capacitance C .

RESONANCE-CAPACITANCE-Exercise - 2
  1. The equivalent capacitance of the combination shown in the figure be...

    Text Solution

    |

  2. The electric field between the plates of a parallel-plate capacitor of...

    Text Solution

    |

  3. A capacitor of capacitance C charged by battery at V volt and then di...

    Text Solution

    |

  4. Hard rubber has a dielectric constant of 2.8 and a dielectric strengh...

    Text Solution

    |

  5. Two square metal plates of side 1 m are kept 0.01 m apart like a paral...

    Text Solution

    |

  6. Three conducting plates of area 500 cm^(2) area kept fixed as shown....

    Text Solution

    |

  7. Consider the arrangement of parallel plates of the previous problem. ...

    Text Solution

    |

  8. For a charged parallel plate capacitor shown in the figure, the force ...

    Text Solution

    |

  9. On a parallel plate capacitor following operations can be performed ...

    Text Solution

    |

  10. In an isolated parallel plate capacitor of capacitance C the four su...

    Text Solution

    |

  11. In the figure shown the plates of a parallel plate capacitor have uneq...

    Text Solution

    |

  12. Rows of capacitors 1,2,4,8 …..infty capacitors, each of capacitance 2 ...

    Text Solution

    |

  13. Shows a diagonal symmetric arrangement of capacitors and a battery. ...

    Text Solution

    |

  14. Two capacitors of 2muF and 3muF are charged to 150 V and 120 V, respec...

    Text Solution

    |

  15. In the adjoining diagram all the capacitors are initially uncharged, ...

    Text Solution

    |

  16. In the circuit shown in figure the switch S is closed at t = 0. A lo...

    Text Solution

    |

  17. When a charged capacitor is connected with an uncharged capacitor , t...

    Text Solution

    |

  18. In the circuit shown each capacitor has a capcitance C. The emf of the...

    Text Solution

    |

  19. Two similar condensers are connected in parallel and are charged to...

    Text Solution

    |

  20. We have a combination as shown in following figure. Choose the corre...

    Text Solution

    |