Electromagnetic Waves

Step 1: Understanding electromagnetic induction.
The phenomenon of electromagnetic induction is the principle behind the operation of devices like generators and transformers. It involves the generation of an electromotive force (emf) when the magnetic flux through a coil changes.
Step 2: Application in generators.
In a generator, mechanical energy is converted into electrical energy using electromagnetic induction. A coil is rotated within a magnetic field, which induces an emf and generates an electric current.
Step 3: Conclusion.
Thus, the laws of electromagnetic induction are used in the construction of a generator, corresponding to option (D).

Step 1: Understanding the electromagnetic spectrum.
The electromagnetic spectrum consists of waves of different wavelengths. From longest to shortest wavelength, the order is: Radio waves have the longest wavelength among the options.
Step 2: Conclusion.
Thus, radio waves have the longest wavelength, corresponding to option (D).

Step 1: Formula for induced emf.
The induced emf is given by Faraday's law of electromagnetic induction: where is the magnetic flux and is the rate of change of flux. Step 2: Substituting known values.
Given that the flux and the time interval , the rate of change of flux is: Step 3: Calculating the induced emf.
The induced emf is: The negative sign indicates the direction of the induced emf according to Lenz’s law, but the magnitude of the emf is . Step 4: Conclusion.
Thus, the induced emf in the wire is .