NCERT

Simple microscope: When the object is placed within the focal length, the simple microscope works on the principle of producing an erect, virtual and magnified image. To magnify small objects, the simple microscope uses a single convex lens.
Compound microscope: It uses two lenses including an eyepiece and objective. The objective lens creates a real, magnified, and inverted image which acts as the object for the eyepiece, which in turn magnifies it further.

In Ray Optics And Optical Instruments questions, when using lens and mirror formulas, sign convention helps in maintaining consistency. The sign convention determines whether quantities like image distance, object distance, and focal length are taken as positive or negative. The incorrect usage of these sign conventions mostly leads to wrong magnifications and image positions. For accurate results, it is essential to follow the Cartesian sign.

The EM wave speed in a vacuum is determined by the permeability and permittivity of free space. It is given by the formula:

$c=\frac{1}{\sqrt{?0_{}?0_{}}}$

The constant value is around $3*{10}^8\text{ m/s.}$

This speed forms the basis for many scientific and technological applications. It is a fundamental physical constant.

The electric field (E) and magnetic field (B) in an electromagnetic wave are always perpendicular to each other and to the direction of wave propagation. The EM waves are transverse in nature. When the EM waves are moving along the X-axis, then along the y-axis, the electric field may oscillate and the magnetic field along the z-axis.

Maxwell introduced the displacement current which ensures that when the conduction current is absent, the current continues in the circuits, such as in the capacitors. The displacement current plays a significant role in the derivation of electromagnetic waves. It shows that an electric field that is changing can produce a magnetic field. In free space, it enables wave propagation.

The capacitive reactance is equal to the inductive reactance at resonance:

$X_L=X_C??=\frac{1}{\sqrt{L?C}}$

In an AC circuit, the power factor cos? measures the efficiency of power usage. Between the current and voltage, it is the cosine of the phase angle. A power factor of 1 means all the supplied power is used effectively and a low power factor means more energy is wasted.

Average power:

$P=V_{\text{rms}}\cdot I_{\text{rms}}\cdot cos??$

The alternating current's RMS (Root Mean Square) value or voltage offers the equivalent DC value that would generate the same power in a resistive circuit. The RMS is used in most practical measurements and is calculated as:

$I_{\text{rms}}=\frac{I_0}{\sqrt{2}},V_{\text{rms}}=\frac{V_0}{\sqrt{2}}$

Where ?0 and ?0 are the peak current and voltage, respectively.

Students can expect conceptual questions on Faraday's and Lenz's Laws, derivations involving EMF, flux calculations, and application-based questions like the functioning of generators or transformers. Numerical problems involving   and time-varying magnetic fields are also frequently included.