Matter:

Matter is anything that has mass and occupies space. It makes up everything in the universe, from the air we breathe to the solid objects we can touch. Matter exists in three primary states: solid, liquid, and gas.

Molecule:

A molecule is a group of two or more atoms bonded together. Molecules can be made up of the same type of atom, like oxygen (O₂), or different types of atoms, like water (H₂O). The atoms within a molecule are held together by chemical bonds.

Atom:

An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus (made up of protons and neutrons) surrounded by electrons in orbitals. Atoms combine to form molecules, and each element is made up of one type of atom. For example, a water molecule (H₂O) is made up of two hydrogen atoms and one oxygen atom.

structure of atom

The structure of an atom consists of three main subatomic particles: protons, neutrons, and electrons.

Nucleus:

• At the center of the atom, there is a dense core called the nucleus. The nucleus contains two types of subatomic particles:

Protons:

• These have a positive charge (+) and are located in the nucleus. The number of protons in the nucleus determines the atomic number and the identity of the element.

Neutrons:

• These are neutral particles (no charge) that are also found in the nucleus. Neutrons and protons have approximately the same mass.

Electrons:

• These are negatively charged particles (-) and orbit the nucleus in energy levels or electron shells. Electrons have much less mass compared to protons and neutrons.

Kirchhoff’s Current Law (KCL)

• Krichhoffs Current Law states that the total current entering a junction or node in an electrical circuit is equal to the total current leaving the node. This law is based on the principle of conservation of electric charge.
• In other words, Kirchhoof’s  current law states that the algebraic sum of alls currents at any node or junction is zero
• Mathematically, KCL can be expressed as:

​Where:

• ∑I_in​ is the sum of all currents flowing into the node.
• ∑I_out​ is the sum of all currents flowing out of the node.

Problem 1: In a certain circuit, three currents meet at a node. The first current, I₁=10A, is entering into the node. The second current, I₂=4 A is also entering into the node. The third current, I₃=2A, is leaving the node. Calculate the value of the fourth current, I₄, leaving the node.

• According to KCL, the algebraic sum of currents at a node must be zero. The sum of currents flowing into the node should be equal to the sum of currents flowing out.

Problem 2: At a junction in an electrical circuit, the following currents are present:

• I₁​=8A entering the node,
• I₂=3   (leaving the node,)
• I₃=5 A (leaving the node).

Calculate the current I₄​ entering the node.

Problem 3: At a junction, there are three currents:

• I₁=7 A entering the junction,
• I₂=5A entering the junction,
• I₃= 10A leaving the junction.

Calculate the value of the fourth current, I₄ leaving the junction.

Kirchhoff’s Voltage Law:

Kirchhoff’s Voltage Law states that the sum of all voltages around a closed loop in a circuit is always equal to zero.

• This law is based on energy conservation, meaning that the components in the loop completely use the total energy supplied by the sources.

• Assumption entering current is taken as positive and leaving current as negative.

Semiconductor Materials:

• semiconductor materials are materials that can conduct electricity, but not as well as metals. They are used in many electronic devices, such as computers and phones. Their ability to conduct electricity can be changed by adding small amounts of other materials

Types of Semiconductors

• Semiconductors can be broadly classified into two main types: Intrinsic Semiconductors and Extrinsic Semiconductors. 

1. Intrinsic Semiconductors

• Intrinsic semiconductors are made from pure elements like silicon (Si) or germanium (Ge), which are naturally semiconducting. These materials have an equal number of free electrons and holes at absolute zero temperature. The electrical conductivity of intrinsic semiconductors depends on factors like temperature, with conductivity increasing as the temperature rises.

• Examples of Intrinsic Semiconductors are Silicon and germanium are the most common examples of intrinsic semiconductors. Silicon, in particular, is widely used in the electronics industry due to its abundance and stable properties.

2.Extrinsic Semiconductors

• Extrinsic semiconductors are semiconductors that have been specially treated by adding impurities to improve their ability to conduct electricity. By adding certain elements, like donor or acceptor atoms, the semiconductor’s properties can be adjusted for different uses.

Doping 

• Doping is the process of adding impurities to a semiconductor material to change its electrical properties. The two main types of extrinsic semiconductors are:
• Based on the type of impurities added, extrinsic semiconductors are classified into two types. They are N-type and p-type semiconductors.

N-type semiconductor:

• An N-type semiconductor is created by adding pentavalent impurities, like Phosphorus (P), Arsenic (As), and Antimony (Sb), to a semiconductor. The pentavalent atoms have five electrons, one more than the semiconductor, providing extra free electrons. These extra electrons help the material conduct electricity better, and an n-type semiconductor is formed.

P-type semiconductor: 

• A P-type semiconductor is created by adding trivalent impurities, like Boron (B), Aluminium (Al), and Gallium (Ga), to a semiconductor. The trivalent atoms have only three electrons, one less than the semiconductor, creating a ‘hole’ or a missing electron. These holes act like positive charge carriers, allowing the material to conduct electricity. As a result, a p-type semiconductor is formed.

Comparison Between N-type and P-type Semiconductors

Majority Charge Carriers

The majority of charge carriers are the charge carriers that are present in the highest concentration in a given semiconductor material. Their presence is primarily responsible for the conduction of electric current.

• In N-type Semiconductors: Electrons are the majority of charge carriers. This is because N-type semiconductors are doped with donor atoms that add extra electrons to the material, increasing the number of free electrons available to carry current.

• In P-type Semiconductors: Holes are the majority charge carriers. In P-type semiconductors, the material is doped with acceptor atoms that create “holes” in the valence band. These holes act as positive charge carriers and are the primary carriers for current flow in P-type semiconductors.

Minority Charge Carriers

The minority charge carriers are the charge carriers that are present in smaller numbers compared to the majority carriers. While their concentration is lower, they still play a significant role in semiconductor behavior, especially in processes like recombination.

• In N-type Semiconductors: Holes are the minority charge carriers. Although holes do exist in N-type semiconductors, their concentration is much lower than the concentration of free electrons.

• In P-type Semiconductors: Electrons are the minority charge carriers. The concentration of free electrons in P-type semiconductors is lower compared to the holes, which are the majority carriers.

PN Junction

• When a single crystal of semiconductor is treated with both pentavalent (like Boron) and trivalent (like Aluminium) impurities, it creates a special barrier where the two regions (N-Type and P-Type) meet. This barrier stops the flow of charge carriers and is known as the PN Junction.

• The most basic semiconductor component, called a Diode, is a real-life example of how the PN Junction works.

How pn junction is formed?

A PN junction is made by using a single silicon crystal and adding two different types of impurities to it. One side is mixed with a pentavalent impurity (which has 5 valence electrons) to create an N-type region, and the other side is mixed with a trivalent impurity (which has 3 valence electrons) to make a P-type region. In the N-type region, there are more free electrons, and in the P-type region, there are more holes (empty spaces for electrons).

When these two regions are joined together, a boundary is formed between them. At this boundary, electrons from the N-type region start moving into the P-type region, and holes from the P-type side move into the N-type region. This movement of electrons and holes is called diffusion. As they move, electrons and holes combine with each other and cancel out.

After some time, this movement creates a small electric field or potential difference at the junction. This electric field pushes back and stops more electrons and holes from crossing the boundary. As a result, a special area forms near the junction where no free electrons or holes are left. This area is called the depletion region.

The depletion region acts like a barrier that stops the flow of more charge carriers. The thickness of this region depends on how much impurity was added during doping. The place where the P-type and N-type regions meet, including this barrier, is called the PN junction.

What is Biasing?

Biasing means joining an external battery to a PN junction diode to control the flow of current through it.

There are two main types of biasing:

🔹 1. Forward Biasing

• In forward bias, the positive terminal of the battery is connected to the P-type region, and the negative terminal is connected to the N-type region.

• This reduces the depletion region and allows current to flow easily through the diode.
• The diode acts like a closed switch in this case.

Easy to remember:
P to Positive and N to Negative → Forward Bias → Current flows

 2. Reverse Biasing

• In reverse bias, the positive terminal of the battery is connected to the N-type region, and the negative terminal is connected to the P-type region.

• This increases the depletion region, making it harder for current to flow.
• The diode acts like an open switch in this case.
• Only a very small leakage current flows (almost zero).

Easy to remember:
P to Negative and N to Positive → Reverse Bias → No current flow

Frenquetly Asked Questions

1. What is matter?
   Answer: Matter is anything that has mass and occupies space.

2. What are the three common states of matter?
   Answer: The three common states of matter are solid, liquid, and gas.

3. Can matter exist in states other than solid, liquid, and gas?
   Answer: Yes, matter can exist in states like plasma and Bose-Einstein condensate under specific conditions.

4. What is a molecule?
   Answer: A molecule is a group of two or more atoms chemically bonded together.

5. What is an atom?
   Answer: An atom is the smallest unit of matter that retains the properties of an element.

6. What is the difference between an atom and a molecule?
   Answer: An atom is a single unit, while a molecule consists of two or more atoms bonded together.

7. What is an element?
   Answer: An element is a pure substance made of only one type of atom.

8. What is a compound?
   Answer: A compound is a substance formed by the chemical combination of two or more different types of atoms.

9. Can you give an example of an element?
   Answer: Oxygen (O₂) is an example of an element.

10. Can you give an example of a compound?
    Answer: Water (H₂O) is an example of a compound.

11. What is atomicity?
    Answer: Atomicity is the number of atoms present in a molecule of a substance.

12. What is the atomicity of oxygen (O₂)?
    Answer: The atomicity of oxygen (O₂) is 2.

13. What is a monatomic molecule?
    Answer: A monatomic molecule consists of only one atom, e.g., helium (He).

14. What is a diatomic molecule?
    Answer: A diatomic molecule consists of two atoms, e.g., oxygen (O₂).

15. What is a polyatomic molecule?
    Answer: A polyatomic molecule consists of more than two atoms, e.g., ozone (O₃).

16. What are the subatomic particles in an atom?
    Answer: The subatomic particles are protons, neutrons, and electrons.

17. What is the charge of a proton?
    Answer: A proton has a positive charge.

18. What is the charge of an electron?
    Answer: An electron has a negative charge.

19. What is the charge of a neutron?
    Answer: A neutron has no electric charge.

20. Where are protons and neutrons located in an atom?
    Answer: Protons and neutrons are located in the nucleus of an atom.

21. Where are electrons found in an atom?
    Answer: Electrons orbit the nucleus in specific energy levels or shells.

22. What is the atomic number of an element?
    Answer: The atomic number is the number of protons in the nucleus of an atom.

23. What determines the identity of an element?
    Answer: The number of protons (atomic number) determines the identity of an element.

24. What is the mass number of an atom?
    Answer: The mass number is the total number of protons and neutrons in an atom’s nucleus.

25. What is an ion?
    Answer: An ion is an atom or molecule that has gained or lost electrons, resulting in a net electric charge.

26. What is a cation?
    Answer: A cation is a positively charged ion formed by losing electrons, e.g., Na⁺.

27. What is an anion?
    Answer: An anion is a negatively charged ion formed by gaining electrons, e.g., Cl⁻.

28. What is Dalton’s atomic theory?
    Answer: Dalton’s atomic theory states that matter is made of indivisible atoms, and atoms of the same element are identical.

29. According to Dalton’s theory, what happens in a chemical reaction?
    Answer: In a chemical reaction, atoms are rearranged, not created or destroyed.

30. Are atoms visible to the naked eye?
    Answer: No, atoms are too small to be visible to the naked eye.

31. What instrument is used to observe atoms?
    Answer: A scanning tunneling microscope (STM) or atomic force microscope (AFM) is used to observe atoms.

32. Can atoms be divided into smaller parts?
    Answer: Yes, atoms can be divided into subatomic particles like protons, neutrons, and electrons.

33. What is the nucleus of an atom?
    Answer: The nucleus is the central part of an atom containing protons and neutrons.

34. What holds the nucleus together?
    Answer: The strong nuclear force holds the nucleus together.

35. Why don’t electrons fall into the nucleus?
    Answer: Electrons are held in their orbits by the electrostatic force and their wave-like properties.

36. What is a chemical bond?
    Answer: A chemical bond is a force that holds atoms together in a molecule or compound.

37. What is a molecule of an element?
    Answer: A molecule of an element consists of atoms of the same element, e.g., O₂.

38. What is a molecule of a compound?
    Answer: A molecule of a compound consists of atoms of different elements, e.g., H₂O.

39. Can a molecule be made of a single atom?
    Answer: Yes, noble gases like helium (He) exist as monatomic molecules.

40. What is the significance of the atomic number?
    Answer: The atomic number determines the element’s position in the periodic table and its chemical properties.

41. What is an isotope?
    Answer: Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

42. Can you give an example of isotopes?
    Answer: Carbon-12 and Carbon-14 are isotopes of carbon.

43. What is the role of electrons in chemical reactions?
    Answer: Electrons are involved in forming chemical bonds during chemical reactions.

44. What is the valency of an atom?
    Answer: Valency is the combining capacity of an atom, determined by the number of electrons it can gain, lose, or share.

45. Why are noble gases chemically inert?
    Answer: Noble gases are chemically inert because they have a complete outer electron shell.

46. What is a molecule’s molecular formula?
    Answer: A molecular formula shows the types and numbers of atoms in a molecule, e.g., H₂O.

47. What is the difference between a molecule and a compound?
    Answer: A molecule is any group of bonded atoms, while a compound is a molecule made of different types of atoms.

48. What is the smallest particle of a compound?
    Answer: The smallest particle of a compound is a molecule or formula unit.

49. How are atoms arranged in a solid?
    Answer: In a solid, atoms are closely packed and arranged in a fixed, orderly pattern.

50. How are atoms arranged in a gas?
    Answer: In a gas, atoms or molecules are far apart and move freely in a random manner.