Exams › JEE Advanced › Physics
A parallel-plate capacitor of capacitance C is connected to a battery and charged to a potential difference V. With the battery still connected, the separation between the plates is slowly reduced to half its original value. What is the work done by the external agent during this process?
- 1/2 * C * V²
- C * V²
- -1/2 * C * V²
- -C * V²
Correct answer: -1/2 * C * V²
Solution
With V fixed, new capacitance is 2C. Energy stored increases from (1/2)CV² to CV². Battery does work CV² (supplies extra charge CV at potential V). By energy conservation, W_external = delta_U - W_battery = (1/2)CV² - CV² = -1/2*CV².
Related JEE Advanced Physics questions
- A particle with charge -q and mass m revolves in a circular path of radius r around an infinitely long charged wire with linear charge density +λ. What is the time period of its motion?
- What is the value of the electrostatic potential at point H?
- The electric potential V varies with distance x from a fixed point as follows: V = 5 V for 0 <= x < 10 m, then V decreases linearly from 5 V at x = 10 m to -10 V at x = 20 m. The electric field at x = 13 m is:
- Two capacitors are connected in a circuit with two batteries and a switch S. The system is in steady state with S open. When S is closed, which of the following statements correctly describes the energy exchange?
- In a capacitor bridge circuit, four capacitors C1, C2, C3, and C4 are connected in a bridge configuration with an EMF source E. Capacitor C1 is in the top-left arm, C2 in the top-right arm, C3 in the bottom-left arm, and C4 in the bottom-right arm. Points P and Q are the mid-points (junctions). Find the potential difference V_P - V_Q.
- An isolated charged spherical soap bubble of radius r has the pressure inside equal to atmospheric pressure outside. The surface tension of the soap solution is T. If the total charge on the bubble can be written as N*pi*r*sqrt(2*T/epsilon0), find the integer value of N.
⚔️ Practice JEE Advanced Physics free + battle 1v1 →