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Why does a Capacitor Block DC but Allow AC?

A capacitor stores electric charge and allows current only while its voltage is changing. ●DC: The voltage becomes constant after the capacitor is fully charged, so dV/dt = 0. Hence, current becomes zero. Therefore, a capacitor blocks DC. ●AC: The voltage continuously changes with time, so dV/dt ≠ 0. The capacitor continuously charges and discharges, allowing current to flow. Therefore, a capacitor allows AC.

Why Does Temperature Remain Constant During a Phase Change?

During a phase change, the heat supplied to a substance is used to overcome intermolecular forces and change its molecular arrangement, rather than increasing its temperature. This energy is called latent heat. For example, while ice melts at 0°C, its temperature remains 0°C until all the ice has melted.  So, even though temperature remains constant, internal energy changes.

Entropy

Entropy(S) is a thermodynamic state function that measures the degree of energy dispersal or randomness/disorder of a system. Unit:- J K-¹ For Specific entropy  Unit :- J Kg K-¹   ●                         dS=dQ/T For reversible process ds=0 For irreversible process ds>0 Examples :- ●Ice melting → entropy increases. ●Water evaporating → entropy increases. ●Gas expanding freely → entropy increases. ●Heat naturally flowing from hot to cold → total entropy increases.

Electromagnetic induction.

Electromagnetic induction is the phenomenon of production of an induced emf (electromotive force) in a closed circuit whenever the magnetic flux linked with the circuit changes. The induced emf is given by e=-dΦ/dt For a coil of N-turns e=-NdΦ/dt where magnetic flux is Φ=BAcosθ Lenz's law:- The induced current always flows in such a direction that it opposes the change in magnetic flux that produces it.

What is resonance?

Resonance is the phenomenon in which a system oscillates with maximum amplitude when the frequency of the external periodic force equals its natural frequency.

What is a wavefunction?

A wave function (ψ) is a mathematical function that describes the quantum state of a particle. Its squared magnitude gives the probability density of finding the particle at a particular position. |ψ|² = Probability density In short : The wave function tells us what we can know about a quantum particle and where it is likely to be found.

Quantum Tunneling.

Quantum tunneling is a phenomenon where a quantum particle can pass through a potential barrier even when its energy is less than the barrier height. In classical physics: ❌ Impossible In quantum physics: ✅ Possible Example : It is responsible for α-decay and is used in scanning tunneling microscopes (STM).