Pooza Creations

Enhancement type MOSFETS: These types of MOSFETS do not have channel formed during its construction. The voltage applied to the gate develops a channel of charge carriers. So, that a current flows when a voltage is applied across the drain source terminals. A channel is said to be enhanced by the application of suitable gate-source bias voltage. So, it is called enhancement MOSFET. There can be both n-channel & p-channel in E-MOSFETS.

Depletion type MOSFETS: These types of MOSFETS already have a channel present in it even when no gate voltage applied. The voltage applied to the gate determines whether the channel is increased or decreased. For an n-channel D-MOSFETS, if the channel is increased by applying positive gate voltage, then the channel is said to be enhanced or enhancement mode. If the channel is decreased by applying negative gate voltage, then the channel is said to be depleted or depletion mode. Hence, a D-MOSFET can be operated in both enhancement as well as depletion mode.

Reverse bias: A diode is said to be reversed biased if the p-region is connected to the negative terminal and n-region is connected to positive terminal of the battery. In a reversed biased diode, the depletion region of the n-type material will increase due to the large number of free electrons drawn to the positive potential of the applied voltage. Similarly, the number of uncovered negative ions in the p-type material will increase. Due to this, the depletion region widens establishing a great barrier across the junction. The majority carriers cannot overcome the potential barrier resulting in no flow of current. However, the minority carriers can flow across the junction resulting in a flow of current even in reverse-bias conditions, known as reverse saturation current.

Forward bias: A diode is said to be forward biased if the positive terminal and n-region is connected to the negative terminal of the battery. When a diode is forward biased, the electrons in the p-type material will recombine with the ions near the boundary and hence reduce the width of the region results in a heavy majority flow across the junction. An electron of the n-type material has a strong attraction for the positive potential applied to the p-type material. Similar is the case for the holes present in p-type material. As the applied bias increases in magnitude, the depletion region will continue to decrease in width until, a flow of electrons can pass through the junction resulting in an exponential rise in current.

After the experimental discovery of electromagnetic waves by hertz in 1888, many other electromagnetic waves were discovered by different ways of excitation. The orderly distribution of electromagnetic radiations according to their wavelength or frequency is called the electromagnetic spectrum. Electromagnetic spectrum has a very wide range with wavelength variation from 10⁻¹³ m to 6*10⁶m. The whole electromagnetic spectrum has been classified into different parts and sub parts, in the order of increasing wavelength and according to the type of excitation. There is over lapping in certain parts of the spectrum, showing that the particular radiation can be produced by two methods. However, the physical properties of electromagnetic waves are determined by their wavelength and not by the method of excitation. The most commonly encountered portion of the electromagnetic spectrum is shown in figure. Which gives approximate wavelength and frequency ranges for the various segments. Only a small part of the complete electromagnetic spectrum (wavelength from 400nm to 700nm) is visible to human eye, as the radiations of this part can produce some sensation on the retina of the eye. This part of the spectrum is called visible spectrum. The radiations of different wavelengths in the visible part of the spectrum produce different colors on the retina of our eye.

The usual classification of electromagnetic spectrum is explained below.

A bar magnet strongly attracts an iron piece, but other materials are weakly attracted and some are actually repelled. We may use this response of material to the field of a bar magnet to broadly classify magnetic materials. All magnetic are classified into three categories. These are: diamagnetic, paramagnetic and ferromagnetic materials. The classification depends on the magnetic dipole moment of atoms of the material and on the interactions among the atoms. When the different magnetic materials are placed in a uniform magnetic field, the field lines are changed as shown in figure.

Free oscillations: when a body capable of oscillation is displaced from its equilibrium position and then left free, it begins to oscillate with a definite amplitude and frequency. If the body is not resisted by any kind of friction, the motion continues. Such oscillation is called the free oscillation. The frequency of vibration depends on the intrinsic properties (shape, elasticity etc) of the body which is called as the natural frequency. The force acting on the on the system is the restoring force. For example, when a simple pendulum is displaced from its mean position and then left free, it executes free oscillations. The natural frequency of the simple pendulum is f= (¹/₂π) {root (l/g)}. In absence of frictional forces, the amplitude of the free oscillations would remain constant. However, in actual practice, a complete free oscillation cannot be obtained in nature.

Forced oscillations: when a body is maintained in a state of oscillation by an external periodic force of frequency other than the natural frequency of the body, the oscillation is called the forced oscillation. In such oscillation is equal to the frequency of the periodic force. The external applied force on the body is called the driver and the body set into the oscillations is called driven oscillator.

Light is a form of energy which on entering our eyes gives the sensation of sight, and enables us to see various objects. Since the early times, scientists have made discussion on the true nature of light and have postulated various theories. These are discussed below: