The size of the coil plays a crucial role in determining the amount of magnetic flux it encloses and thus affects the induced emf. A larger coil can encompass more magnetic flux, leading to a higher potential induced emf when the magnetic field changes. However, it’s also essential to consider the coil's resistance, which increases with its size. A balance must be struck to optimise the coil's size for efficient energy conversion while minimising resistive losses to ensure that a significant portion of the induced emf translates into usable electric current.

Theoretically, there is no upper limit to the emf that can be induced according to Faraday's law. The induced emf is directly proportional to the rate of change of the magnetic flux. Therefore, by increasing the rate of change of magnetic flux (either by increasing the magnetic field strength, changing the magnetic field more rapidly, or both), the induced emf can be increased. However, practical limits arise due to the physical properties of materials, thermal effects, and other real-world constraints, which can affect the actual emf induced in a given situation.

Yes, an induced emf can certainly occur if the magnetic field source is moved while the coil remains stationary. Faraday’s law is concerned with the relative motion between the coil and the magnetic field. It's the change in magnetic flux through the coil that matters, not specifically the motion of the coil or the magnet. In applications like electric generators, the coil is often rotated to change the magnetic flux through it. However, a similar effect, and thus induced emf, can be achieved by moving the magnetic field source instead while keeping the coil stationary.

The material of the coil can significantly influence the induced emf. Different materials have varying levels of electrical conductivity, and a coil made of a highly conductive material will have a lower resistance, allowing a higher induced current to flow. While Faraday's law itself doesn't directly consider the material of the coil, the induced emf’s effectiveness in generating an electric current is certainly influenced by the coil’s material. For instance, coils made of copper, a highly conductive material, are often used to ensure efficient induction and minimal energy loss.

Faraday's Law of Induction is not restricted by the shape or geometry of the coil. The law is based on the change in magnetic flux through any closed loop or circuit. The shape of the coil can certainly influence the total magnetic flux through it due to variations in the area encompassed by different portions of the coil. However, Faraday’s law, ε = -NΔΦ/Δt, remains applicable. The efficiency and effectiveness of the induction process may vary with coil shape, but the foundational principle of a changing magnetic field inducing an emf remains constant across different geometries.