The idea of a mechanical device, like a wind up toy, is to take take advantage of the laws of thermodynamics in order to perform some kind of work.
In the case of a wind up toy, mechanical energy (winding the handle) is stored as potential energy in an internal spring. This creates a state of 'low entropy' in the toy since work was done to concentrate energy in the spring.
The natural tendency of the spring is to unwind and distribute it's energy in a more disordered fashion, thereby increasing entropy and following the laws of thermodynamics.
The mechanism inside the toy is engineered to focus the flow of energy being delivered by the spring into a specific mechanical motion (Kinetic Energy), then sound (air pressure) and finally heat (thermal energy).
In rivers that are close to sea
The substance that loses electrons is being oxidized and is the reducing agent.
Answer:
1) Option D is correct.
The electric field inside a conductor is always zero.
2) Option A is correct.
The charge density inside the conductor is 0.
3) Charge density on the surface of the conductor at that point = η = -E ε₀
Explanation:
1) The electric field is zero inside a conductor. Any excess charge resides entirely on the surface or surfaces of a conductor.
Assuming the net electric field wasn't zero, current would flow inside the conductor and this would build up charges on the exterior of the conductor. These charges would oppose the field, ultimately (in a few nanoseconds for a metal) canceling the field to zero.
2) Since there are no charges inside a conductor (they all reside on the surface), it is logical that the charge density inside the conductor is also 0.
3) Surface Charge density = η = (q/A)
But electric field is given as
E = (-q/2πε₀r²)
q = -E (2πε₀r²)
η = (q/A) = -E (2πε₀r²)/A
For an elemental point on the surface,
A = 2πrl = 2πr²
So,
η = -E ε₀
Hope this Helps!!!