NCERT

The entire range of electromagnetic radiation, arranged to increase and decrease the wavelength is called the electromagnetic (EM) spectrum. In the following order, it includes - radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All these regions have unique properties and applications. For example, X-rays used in medical imaging,  visible light in everyday vision, infrared in remote controls and thermal imaging and radio waves are used in communication. This is an important concept that helps in classifying and utilizing different EM waves.

The photoelectric effect when light is projected in a metal surface, it's surface ejects electron (which are in outermost shell or free electron). This happens because the light provides additional energy to the electron to detach itself from metal surface. Well to do this light must have a certain amount of energy which in other words can be said the right frequency of light is required for photoelectric effect. 

This frequency must be above a certain minimum value (called threshold frequency) fixed for every metal, regardless of its intensity. Photoelectric effect cannot be explained by the wave theory of light.

The net magnetic flux through any closed surface is zero, according to Gauss's Law for magnetism.
Mathematically,
? B · dA = 0.
It states that all magnetic field lines that enter a surface must exit from it as well. In this way, it is different from the electric charges which can exist independently as positive and negative.

The Earth's magnetic field makes a magnetic inclination or dip with the horizontal plane at a particular location. It shows how much the magnetic field is tilted from the horizontal. It gets tilted due to the Earth's magnetic nature. The formula is:
tan I = B_V / B_H,
where B_V is the vertical component and B_H is the horizontal component of the Earth's magnetic field.

The angle between the magnetic north (the direction a compass points) and the geographic north (true north) is the magnetic declination. This angle can change over time due to changes in the Earth's magnetic field and varies with location on Earth. It is important for navigation where accurate directional orientation is crucial, especially in marine and aviation transport. The declination helps in avoiding navigational errors as it ensures that compass readings are corrected.

The Earth's magnetic field makes a magnetic inclination or dip with the horizontal plane at a particular location. It shows how much the magnetic field is tilted from the horizontal. It gets tilted due to the Earth's magnetic nature. The formula is:
tan I = B_V / B_H,
where B_V is the vertical component and B_H is the horizontal component of the Earth's magnetic field.

In a magnetic dipole, two equal and opposite magnetic poles are kept at a small distance. In concept, it is equal to an electric dipole. The magnetic dipole moment (M) represents the strength and orientation of the magnetic dipole and it is a vector quantity. The formula is: M = m * 2l. Here m represents the pole strength and 21 shows the distance between the poles. The direction of M is from the south pole to the north pole of the magnet, and its SI unit is A·m².

The region around a moving electric charge or a magnetic material where the force of magnetism acts is called the magnetic field. The magnetic field lines are used to represent the strength and direction of the magnetic field and these are imaginary lines. The density of these lines shows the field strength. The magnetic field emerges from the magnet's north pole and enters the south pole. The magnetic field is stronger for the closer lines. These lines always form closed loops and never intersect each other. It differentiates it from the electric field which starts or ends on charges.