# Chapter 7 Alternating Current Class 12 Notes – Physics

## Chapter 7 Alternating Current Class 12 Notes

Alternating Current (AC): A constant shift in the amount of alternating current occurs throughout time, and its polarity is switched on a regular basis. It is symbolised by

RMS Value of AC (Effective Value): It is described as the AC value throughout a full cycle that produces the same quantity of heat in a particular resistor as steady current in the same resistor at the very same period throughout a full cycle.

Over just a cycle that is positive half, the mean or average value of alternating current is 0.637 times the peak value or 63.7 per cent of the peak value.

Phasor Diagram: Current and voltage are in phase in the a.c. the circuit including only R. As a result, both phasors I0 and E0 are pointing in the same orientation in the picture, forming an angle (t) with OX. This holds true in all situations. It means that across R, the phase angle across alternating voltage and alternating current is 0.

Inductive Reactance (XL): Inductive reactance is the property of an inductor that opposes current flow.

Capacitive Reactance (Xc): Capacitive reactance is the property of a capacitor that opposes the transfer of alternating current.

Wattless Current: Wattless current, also known as idle current, is the current in an AC circuit whenever the average power consumption is 0.

Energy Loss in Transformers:

• Copper loss refers to heat dissipation in a transformer’s copper coils. Conducting lines are heated by Joules, which causes this. Utilizing thick cables, these are minimised.
• Heat loss in the iron transformer core is known as iron loss. Eddy currents arise in the iron core, which causes this. Using laminated cores helps to reduce this.
• Hysteresis loss is one of the factors to consider. When a.c. is supplied to the iron core, this is the energy loss caused by repetitive magnetisation and demagnetisation. By employing a magnetic material with low hysteresis loss, the loss is limited to a bare minimum.

Displacement Current’s Consequences: According to Maxwell’s theory, a changing electric field causes displacement current, which further generates a magnetic field comparable to conduction current. In reality, it is a mirrored equivalent of Faraday’s hypothesis that prompted Maxwell to infer that the displacement current is also a generator of the magnetic field. It indicates that the time-varying electric and magnetic fields cause one another to exist. Maxwell deduced the presence of electromagnetic waves in a location where electric and magnetic fields changed with time based on these notions.

Electromagnetic Spectrum: Several other electromagnetic waves were identified by other means of activation after Hertz’s practical finding of electromagnetic waves. The electromagnetic spectrum is the systematic dispersion of electromagnetic radiations as per their wavelength or frequency.

Radiowaves: These are electromagnetic waves that range in frequency from 5105Hz to 109Hz. Fluctuating electric circuits with an inductor and capacitor generate these waveforms.

• The amplitude modulated (AM) band is formed by electromagnetic waves with a frequency range of 530 kHz to 1710 kHz. It is employed in the propagation of ground waves.
• Short wave bands utilise electromagnetic waves with frequencies ranging from 1710 kHz to 54 Mhz. It is employed in the propagation of sky waves.
• Television waves utilise electromagnetic waves with a frequency range of 54 to 890 MHz.
• Electromagnetic waves in the 88 MHz to 108 MHz frequency range from the frequency modulated (FM) radio spectrum. It’s a professional FM radio station.

Microwaves: Microwaves are electromagnetic waves with a frequency range of one to three gigahertz (GHz). Special vacuum tubes are used to create them. Specifically, klystrons, magnetrons, and Gunn diodes.

Uses of Microwaves:

• A microwave-based radar can identify the speed of a frisbee, golf ball, or vehicle in motion.
• Microwave ovens are utilised in the kitchen.
• Microwaves are employed in microwave-operated control centers to observe the passage of trains on tracks.

Infrared Waves: Herschell was the first to discover infrared waves. Electromagnetic radiation with a frequency range of 3*10^11 Hz to 4*10^14 Hz is what we’re talking about. Heatwaves are another name for infrared waves. Hot bodies and substances produce infrared waves. These waves are undetectable to the naked eye, but they are detectable by snakes.

Uses of Infrared Waves:

• To cure muscular tension in physiotherapy.
• Using solar cells to provide electric power to satellites
• For the production of dried fruits
• For photographing in fog, haze, and other similar conditions.
• To preserve the vegetation warm in greenhouses
• In unveiling the old walls’ secret writings
• Solar cookers and water heaters

Visible Light: It’s a small portion of the electromagnetic spectrum that can be seen with the naked eye. It has a frequency range of 4*10^14 Hz to 8*10^14 Hz. Atomic excitation causes it to be created. The visible light generated or mirrored by the things in our environment supplies us with information about the world around us.

Ultraviolet Rays: Ritter discovered the UV rays in 1801. Ultraviolet photons have a frequency range of 8*10^14 Hz to 5*10^16 Hz. UV rays are generated by the sunlight, special lighting, and extremely heated bodies. The ozone layer in the stratosphere absorbs the majority of the sun’s UV rays. UV rays have a detrimental impact on people’s eyes when they are in excessive amounts.

Uses of Ultraviolet Rays:

• To examine mineral samples utilising the fluorescence-causing characteristic of UV light. UV absorption spectra of electrons in the exterior shell
• In order to kill microorganisms and sterilise medical instruments.
• It is used in many burglar alarms.
• Fingerprints in forensic laboratories are used to detect fraudulent information.
• To keep the food fresh.

X-Rays: W. Roentgen, a German physicist, was the first to identify X-rays. They have a frequency range of 10^16 Hz to 3*10^21 Hz. Whenever high-energy electrons are stopped abruptly on a metal with a high atomic number, they are created. X-rays have a great deal of penetration strength.

Uses of X-Rays:

• Cracks, foreign things such as bullets, sick organs, and gallstones in the human body are all detected during surgery.
• In engineering, for identifying defects, cracks, imperfections, and perforations in finished metal goods, as well as soldering, foundry, and mould testing.
• To treat undetected skin disorders and cancerous growths using radiotherapy.
• In investigative divisions for bombs, opium, gold, and silver detection in traffickers’ bodies.

γ-Rays: γ-rays are electromagnetic waves with frequencies ranging from 3*10^18 Hz to 5*10^22 Hz. The origin of γ -rays is nuclear. The nucleus of radioactive material produces these rays, which are extremely intense.

Uses of γ-Rays:

• In the prevention and treatment of cancer and malignancies.
• To keep food fresh for a long time since soft rays may readily kill bacteria.
• In order to generate nuclear reactions.
• To contribute to the understanding of the constitution of the atomic nucleus.

## Summary – Chapter 7 Alternating Current Class 12 Notes

This chapter 7 alternating current class 12 notes will assist you in fully comprehending the chapter so that you can examine the important subjects and accurately answer the chapter’s problems on the examination. You can save a huge amount of time studying the chapter for your examinations if you use these notes.

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