Category: Physics Notes PPT

The direct current meaning is when the electrical current flows consistently in a single direction. Direct current is produced by rectifiers, batteries, generators with commutators, and fuel cells. For example, the current flowing in appliances running on batteries or in a flashlight is a direct current. The most common use and essentiality of direct current is electroplating. Direct current was supplanted by AC currents (alternating current) for typical commercial power.

AC DC current is one of the most important topics covered in Physics. Alternating Current or AC currents is defined as a type of electrical current in which the electron flow direction alternates back and forth at regular cycles or time intervals. The typical example of current AC is the current flowing household electricity and power lines from a wall outlet. You can use any electrical appliance in India if it meets the standard voltage of 230 Volts and the frequency of 50 Hertz. 

Difference Between Direct Current and Alternating Current

The primary difference between AC and DC currents are-

The current which changes its direction at regular cycle or time intervals are defined as current AC or Alternating current. Direct current meaning states unidirectional or that current DC flows in only one direction. 

A significant difference between AC current and DC current is that the alternating current frequency is between 50 to 60 Hertz. In contrast, Direct current’s frequency remains zero as per the country’s standard guidelines. 

An alternator generates the Alternating current while the Direct current is generated by cells, generator, and battery. 

A few substations require AC for the generation and transmission of electricity, while extra substations require electricity transmission through Direct currents.  

The DC and AC current is often inter-converted based on the need. The alternating current is converted into a Direct current using a rectifier, whereas the Direct current is transformed into an Alternating current using an inverter.

AC-DC current holds large applications. AC currents are used in factories, household purposes, and industries, while DC mainly uses flash lighting, electrolysis, electronic equipment, hybrid vehicles, etc.

Similarities Between DC And AC Current

Both AC current DC current results from the induced charge that moves through wires to transmit electrical energy and then use it to power various other devices. 

In AC-DC current, negative electron flow produces the electrical current, and both the currents are harnessed energy that can be tapped. The current flow through a conductor, such as power lines between the device and the power source, uses the power. The negative electrons flow through the line as they are attracted towards the positive charge. 

In both AC current and DC current, a voltage source initiates the current flow in the circuits, converting from one type of current to the other and is considered more accessible.

Application of Direct Current and Alternating Current

The Application of DC is in-.

Batteries: Both non-rechargeable and rechargeable batteries can only supply current DC. However, the rechargeable batteries need regular recharging when using the DC.

Electronic Equipment: All major equipment like cellphones, computers, radios, and all electronic equipment use DC to power the electronic circuits.

Specific Electrical Equipment: Although most electrical equipment uses AC, a few of them use direct current.

Solar Panels: Solar panels mainly produce direct current. However, when used with an AC main to supply local AC power, an inverter is required to enable the direct current, DC from the solar panels and convert it into AC.

The Application of AC is-

The alternating current is used primarily for power distribution and holds a significant advantage in that it can easily be converted to other voltages using a simple transformer. Transformers do not work with DC power.

Alternating current is mainly used in the industry of the production and transportation of electricity. Almost every household across the globe is powered by AC as DC is generally not used and preferred for these purposes as it is more power lost to heat than AC. This might also lead to higher risks of producing fire, issues, and even higher costs while converting high voltage and low current to low voltage and high current using a transformer.

AC is also the current used to electric power motors, which converts electrical energy into mechanical energy. Most of the household appliances that we use that rely on AC aren’t limited to garbage disposals, refrigerators, toasters, and dishwashers.

AC is highly popular for power generation because machines generate that power much less expensively, it involves decreasing of voltage, and is easier to produce.

• The attractive forces which are between molecules of the same type are known as the cohesive forces.

• The forces which are attractive between molecules of different types are known as adhesive forces.

• The forces which are Cohesive between molecules that cause the surface of a liquid to contract that too to the smallest possible surface area. This general effect is known as the surface tension.

• The action which is of the capillary action is the tendency of a fluid which is to be raised or suppressed in a narrow tube or the capillary tube which is due to the relative strength of adhesive and cohesive forces.

The adhesive as well as the Cohesive forces are associated with bulk or macroscopic properties and hence we can say that the terms are not applicable to the discussion of molecules and atomic properties. When a liquid that comes into contact with a surface such as which is the walls of a cylinder graduated or a tabletop both cohesive forces and adhesive will act on it. These forces which we are talking about govern the shape which the liquid takes on. 

Due to the effects which are forces which are adhesive the liquid which is on a surface that can spread out to form a thin that relatively uniform film over the surface. In short we can say that a process which is known as wetting. Alternatively we can observe here that in the presence of strong cohesive forces the liquid can divide into a number of small. And even at times roughly spherical beads that stand on the surface which are  maintaining minimal contact with the surface.

Capillary Rise

The action which is of the Capillary sometimes capillarity, capillary motion or wicking is the ability of a liquid to flow that too in a space which is narrow without the assistance of or even we can say in opposition to forces which are  external like gravity. At times in a biological cell. We can more easily define the capillary and the action which is as a phenomenon where ascension of liquids through a tube or we can say the cylinder that takes place. This we can say primarily occurs due to cohesive and adhesive forces.

The liquid which is drawn that too in the upward direction which is due to this interaction between the phenomena. 

The narrower the tube, the higher will the rise in liquid. If any of the two phenomena  that we have discussed about the surface tension and a ratio which is between cohesion to adhesion increase the rise will also increase. Although we can also say that if the density of the liquid increases which is liquid the rise of the liquid in the capillary will lessen.

The amount of water we take  is held in the capillary that also determines the force with which it will rise. The material that really surrounds the files of pores also forms a film over them. The materials which are solid that are nearest to the molecules of water have the greatest property of adhesion. The thickness of the film increases as water is added to the pore and the capillary of magnitude force gets reduced. 

Capillary Rise Equation

A density of liquid denoted by ρ and surface tension denoted by σ rises in a capillary of inner radius denoted by letter r to a height:

That is h= 2σ cosθ/ρ g r

where θ, which we have seen is the contact angle that is made by the liquid meniscus with the capillary’s surface.

The rise in the liquid which is due to the forces of adhesion, cohesion and surface tension as well. If forces which are adhesive the liquid-capillary that is more than the force which is cohesive liquid-liquid then the liquid rises as in case of water rise in a glass capillary. In this case the contact angle is less than 90 degrees and the meniscus is concave. If the force which is adhesive is less than the force which is a cohesive force then liquid depresses as in case of mercury in a glass capillary. In this case which we have discussed, the contact angle is greater than 90 degrees and the meniscus is convex.

The formula for rise in the capillary can be derived by forces which are balancing forces on the liquid column. The weight that is of the liquid πr2hρg is balanced by the force which is upward due to surface tension that is 2πrσcosθ. This formula that we have seen can also be derived using balance pressure.

The capillary which is rised experiment is used to measure the surface tension of a liquid.

Pressure inside a Bubble

We all know the thing already that plants absorb water which is from the soil to make food photosynthesis. But have we ever wondered how this all happens? For instance if we take water to rise up it has to work against gravity and yet it does happen. This is another phenomenon which often occurs which is because of the surface tension of liquids.

If water that we took in our experiments is placed in a beaker or a narrow measuring cylinder we can easily see that the surface of the water is meniscus isn’t straight. It forms a slight amount of depression. Actually, we can observe here that due to adhesive forces which are between surface and water the outer edge is pulled upwards in case of water. An image illustrating all this effect is given below:

The  process of emission and propagation or transmission of energy in the form of waves, particles or rays through a material medium or any space is called Radiation . Radiation can

be of number of types such as heat waves or particle radiation , radio waves , gamma radiation,

microwaves, infrared, visible light, ultraviolet, x-rays ,etc depending upon their nature and characteristics .

Types of Radiation 

Types Of Radiation: Radiation is energy that is emitted by a source, then travels through a medium, such as air, until it is absorbed by matter. Based on the energy of the radiated particles, they are classified as follows:

1 Ionizing radiation

2. Non-ionizing radiation

Ionizing Radiation : Radiation that produces ions with sufficient energy in the matter at the molecular level upon the interaction is called Ionizing Radiation. In other words,  it can remove tightly bound electrons from its  orbit, thus causing the atom to become further charged or ionized , thus when  interacting matter is a human body, resulting in significant damage including damage to DNA and denaturation of proteins.

Since ionizing radiation is caused due to unstable atoms that either have excess energy or mass or both. Therefore to get back to a stable state, they have to release the extra mass or energy in the form of radiation to acquire their initial state .

The different types of Ionizing Radiations are:  

1. Alpha particles

2. Beta particles

3. Gamma rays

4. X-rays

Effects of Radiation on Human Body

Exposure to very high levels of radiation may affect living things by damaging their cells that make up the living organism which  can further cause acute health effects such as skin burns and acute radiation syndrome (“radiation sickness”) .The effects of radiation on a cell are random i.e the same type and amount of radiation could strike the same cell many times and have  different effect, including no effect.  The most common early side effects such fatigue (feeling tired) and skin changes , hair loss, etc.It can also cause mouth problems when radiation treatment is given to this area .

 Whether the source of radiation is natural or man-made, there will be some biological effects that overall may result into Symptoms of radiation sickness may include Weakness, fatigue, fainting, confusion , Bleeding from the nose, mouth, gums, and rectum, bruising, skin burns, open sores on the skin, sloughing of skin, etc whether it is a  small dose of radiation or a large dose.

Following are Biological Effects of Radiation 

(1) Hair : Radiation causes quick losing of hair in clumps generally when 200 rems or higher exposure is there.

(2) Brain: Like the heart, radiation kills nerve cells and small blood vessels, and can cause seizures and immediate death and also  Since brain cells do not reproduce and they won’t be damaged directly until and unless  the exposure is 5,000 rems or greater.

(3) Blood System: the blood’s lymphocyte cell count will be reduced, when a person is exposed to around 100 rems leaving the victim more susceptible to infection and which  is often referred to as mild radiation sickness. symptoms of radiation are  sickness mimic and  of flu and may go unnoticed unless a blood count is done . Data from Hiroshima and Nagaski, suggests that symptoms may persist for up to 10 years and may also have an increased long-term risk for leukemia and lymphoma.

(4) Genetic Effects due to Mutation of the reproductive cells passed onto the offspring of the exposed individual ,also many chemical agents as well as biological agents (such as viruses) that cause mutations.

(5) Heart : Immediate damage to small blood vessels and probably cause heart failure and death directly when there is intense exposure to radioactive material at 1,000 to 5,000 rems

(6) Gastrointestinal Tract : When the victim’s exposure is 200 rems or more,the Radiation damage to the intestinal tract lining will cause nausea, bloody vomiting and diarrhoea . Thus will begin to destroy the cells in the body that divide rapidly. These include blood, reproductive and hair cells, which  harms their DNA and RNA of surviving cells.

(7) Reproductive Tract : Reproductive tract cells divide rapidly thus these  areas of the body can be damaged at rem levels as low as 200. Long-term, some radiation sickness victims will become sterile.

Classification of Radiation Effects

Biological effects of radiation are typically divided into two categories ,the   first category includes exposure to high doses of radiation over short periods of time producing acute or short term effects while the second category represents exposure to low doses of radiation over an extended period of time producing chronic or long term effects. The high doses of radiation tend to kill cells , while low doses tend to change them or damage them . High doses can kill so many cells that tissues and organs are damaged  in turn may cause a rapid whole body response often called the Acute Radiation Syndrome (ARS).  The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years as the low doses often  spread out over long periods of time thus cannot  cause an immediate problem to any body organ.

An electric current is a rate of flowing electric charge past a point or region. An electric current exists when there is a net flow of electric charge through a region. The moving particles are called charge carriers, and there may be different types of particles in different conductors. In electric circuits, the charge carriers are electrons moving through a wire. In an electrolyte, the charge carriers are ions, and in an ionized gas, they are ions and electrons. Electric current is measured through a device called an ammeter. Electric current causes Joule heating, which creates light in incandescent light bulbs. 

Types of Electric Current

1.  Alternating current (AC) — In its systems, the movement of electric charge reverses direction periodically. AC is the form of electric power that is most commonly delivered to businesses and residences. Audio and radio signals that are carried on electrical wires are some examples of AC. 

2. Direct current (DC) — It is the unidirectional flow of electric charge and a system in which electric charge moves in one direction only. Sources of direct current are batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. DC flows in a conductor like wire, but can also flow through semiconductors, insulators, or a vacuum as in electron or ion beams. 

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Ohm’s Law

A law regarding the flow of currents was discovered by G.S. Ohm in 1828 before the physical mechanism responsible for the flow of currents was discovered. Let’s imagine a conductor through which a current I is flowing and let V be the potential difference between the ends of the conductor. Then Ohm’s law states that

V ∝ I

or, V = RI

Here, the constant of proportionality R is called the resistance of the conductor. SI unit of resistance is the ohm, denoted by the symbol Ω. Resistance R depends on both the material and the dimensions of the conductor. 

Conventions

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In a conductive object, the moving charged particles that constitute the electric current are known as charge carriers. In metals, the positively charged atomic nuclei of the atoms are held in a fixed position whereas the negatively charged electrons that are charge carriers that are free to move in the metal. In semiconductors, the charge carriers can be positive or negative, depending on the dopant used. A flow of positive charge gives the electric current and has an effect in a circuit the same as an equal flow of negative charges in the opposite direction. 

Measurement of Current 

Current can be measured using an ammeter. It’s also measured by detecting the magnetic field associated with the current. 

Different Techniques to Measure Current are:

Resistive Heating

Joule heating or resistive heating is a process of power dissipation through which the passage of an electric current through a conductor increases the internal energy of the conductor, converting thermodynamic work into heat. James Prescott Joule, the inventor of this phenomenon, immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current through the wire for 30 minutes. By varying the current and length of the wire, he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the wire.

P ∝ I²R

This relationship is known as Joule’s Law. The SI unit of energy was named joule and given the symbol J. The SI unit of power, watt (W), is equivalent to one joule per second.

Fun Facts

• Up to 3,000 volts can be measured by a spark of static electricity.

• Lightning bolts travel up to 130,000 miles/hour and its temperature can reach around 54,000° F. Lightning is also a discharge of electricity in the atmosphere.

• Electric eels can produce strong electric shocks of around 500 volts for self-defense and hunting.

• Birds sitting on a power line don’t get electrocuted because when a bird sits just on one power line then it is safe but if the bird touches another line with a wing or by its feet, then this creates a circuit which causes the electricity to flow through the bird’s body which results in electrocution.

• Positive charges repel each other and negative charges also do the same. On the contrary, the two opposite charges (positive and negative) attract each other.

• When coal is burned in furnaces that boil water the steam coming from the boiling water helps generate electricity by spinning the turbines that are attached to generators, coal is also the world’s largest source of energy for the production of electricity.

Each material which we have seen till date is different and has its properties and characteristics. Some of the materials which have electrically charged particles generally known as electrons. These electrons that are electric charge that is applied to the material at point which is specific point. The electrons which really start to move and allow electricity to pass through it. 

The materials which have good mobility that are of electrons are called conductors and materials that are with less mobility of electrons that are referred to as insulators. In this article let us know the best electrical conductors and its properties as well.

Classification of Electrical Conductivity

The ability of the material to pass electricity through it is called conductivity. Depending on the conductivity of the materials are classified as conductors or the insulators and superconductors.

If we have to define the meaning that is of electrical conductors that too in the simplest way that is they are materials that allow electricity that too to flow through them easily. If we compare the other two types of material and the first one that allows the better flow of electricity through it then that material is already said to be a very good conductor of electricity.

Examples of Electrical Conductors

Some of the examples that are of conductors of electricity are:

• The Copper

• The Aluminium

• The Silver

• The Gold

• The Graphite

• The Platinum

• The Water

• The People

A conductor which is said to be the electrical conductor allows the electric charges to easily flow through them. The property which is of conductors basically to “conduct” the electricity is known as the conductivity. Such materials offer less opposition or we can say resistance to the flow of charges. The Conducting materials that generally allow easy charge transfer because of the free movement of electrons through them.

Good Electric Conductor

The substance that is of the atom is an electrical conductor that must have no energy gap that is between its band of valence and band of conduction. The electron which is said to be the outer electrons in the valence band are loosely attached to the atom. When an electron gets excited due to force which is the electromotive force or thermal effect, it moves from its valence band to conduction band.

The band which is of Conduction is the band where this electron gets its freedom to move anywhere in the conductor. The conductor is formed by two atoms. Thus, as a whole we can consider that the band which is the conduction is in abundance of electrons. In other words we can say that the bonds which are metallic are present in the conductors. These metallic bonds which are basically based on the structure that is of positive metal ions. These structures are surrounded by clouds of electrons.

Properties of Electrical Conductor Metal

The main properties that we should be with a conductor are listed as follows:

1. A conductor that always allows the movement of free ions and electrons.

2. The field which is said to be the electric field that is inside a conductor must be zero to permit the ions or the electrons to move through the conductor.

3. The Charge density which is inside a conductor that is zero and that is the negative and positive charges that cancel inside a conductor.

4. As we already know that there is no charge inside the conductor that only free charges can exist that too only on the surface of a conductor.

5. The field which is said to be the electric field is perpendicular to the surface of that conductor.

The Solid Conductor

1. The Metallic Conductor: the Silver, and the Copper, and the Aluminum, Gold etc.

2. The Non Metallic Conductor: the Graphite

3. The Alloy Conductor: the Brass, Bronze etc.

The Liquid Conductor

1. The Metallic Conductor: the Mercury

2. The Non Metallic Conductor: the Saline Water and the Acid Solution etc.

A current which is carried as the conductor at any instance is with zero charge. It is so because at any instance the number of electrons  or we can say that at drift velocity it is equal to the number of protons that are in this conductor. So the net charge which is zero.

We can  Suppose that a conductor is connected with or across a battery, that is the positive end and the negative end are connected with a conductor. Now we will notice that the flow of the electrons that are through the conductor are from negative end to positive end of the battery. This flow which we have discussed is electrons is possible until this battery has EMF that has the producing capability through chemical reaction inside.

EM is a short-form that stands for the electromagnetic spectrum. The possibility of the appearance of electromagnetic waves is when both an electric field and a magnetic field come close. 

Some physicists explain that electromagnetic waves are the collection of oscillating magnetic and electric fields. You can find solutions to electromagnetic waves if you analyze Maxwell’s equations. They are called the fundamental equations of electrodynamics. 

You will know in brief the electromagnetic spectrum in this article.

Note: The formation of electromagnetic waves is quite interesting. When a charged particle is in motion, it produces a magnetic field around its perimeter. The magnetic field direction varies with the types of charges. The direction of the magnetic field produced by the positive charge is opposite to the direction of the magnetic field produced by the negative charge.

Types of Electromagnetic Waves

You must have heard of different names of electromagnetic waves. Well, the uses of these waves are very common and significant in many divisions.

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These types of waves are used to broadcast signals for radio and television. This wave has the longest wavelength.

These electromagnetic waves are in the use of cooking, radar, telephone, and other signals.

This wave is beneficial for transmitting heat from the sun, radiators, and fire.

We can see with the help of visible light. 

Ultraviolet radiation is coming from the sun or many nuclear plants. This wave is not good for the skin sometimes. Scientists use this radiation in fluorescent tubes.

This ray helps to get the visuals of organs and other parts. This technology is widely applicable in medical sciences.

• Gamma Rays

• Gamma rays are useful for killing cancer cells. 

• The ray is propagated to infected regions. 

• This wave has the shortest wavelength.

Concepts of Electromagnetic Spectrum Wavelengths

In 1888, Heinrich Hertz had verified a wave that had a speed of visible light. They are called radio waves in the present. The electromagnetic spectrum is responsible for measuring reflection, diffraction, refraction, and polarization.

All of the above properties of visible light can be studied through Maxwell’s waves. Visible light is the best example of the learning of electromagnetic waves. Scientists do not find any theoretical explanation for Electromagnetic Spectrum Wavelengths. 

However, they have parted the spectrum into different regions based on historical developments.

The following figure is the narrow range of visible light in the form of the electromagnetic spectrum.

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Spectrum of Wavelengths

Physicists has categorized electromagnetic waves into certain groups based on their frequencies f. 

 

The wavelength of the electromagnetic wave is equal to λ = c/f. ~400 nm to ~700 nm is the wavelength of visible light whereas ~400 nm is the wavelength of violet light. Its frequency is ~7.5*1014 Hz.

 

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In the full electromagnetic spectrum, visible light has a small part. The following table shows the frequency range and wavelength range of certain electromagnetic waves.

 

Properties of electromagnetic waves

• They are transverse.

• They have the oscillating electric and also magnetic vectors always at right angles which are in the direction of the propagation of the waves.

• They can travel well in a vacuum because they do not require a medium to travel.

• They travel at the speed of light.

• They are produced by the oscillating of the electric charges and also by the transition of electrons between the energy levels from the atom.

 

Applications of the Electromagnetic spectrum 

• Radio waves are transmitted through the air which does not cause damage even if it is absorbed by the human body.

• Microwaves are used in cooking. What happens is when the high-frequency microwaves get absorbed by the food molecules the heating is caused by the increase of the internal energy of the molecules.

• Fiber optic communication uses visible light.

• The sterilization of water using ultraviolet rays.

The Electromagnetic Spectrum

The electromagnetic spectrum definition is very simple. This is the range of all varieties of electromagnetic radiation. Radiation is a type of energy that passes and spreads out to certain areas until the energy level falls to zero. For example, visible light. 

 

Let’s consider the light coming out of a candle has a certain amount of electromagnetic radiation. Also, radio waves that travel to the sky have some amount of electromagnetic radiation.

 

Conclusion

This is all about the electromagnetic spectrum and its different forms. Determine the differences between these electromagnetic waves and learn their uses.