7. Alternating Current
рдЗрд╕ рдкреЗрдЬ рдкрд░ рдЖрдкрдХреЛ 7. Alternating Current рдХреЗ рд╕рднреА рдорд╣рддреНрд╡рдкреВрд░реНрдг рдмрд╣реБрд╡рд┐рдХрд▓реНрдкреАрдп рдкреНрд░рд╢реНрди (MCQ), рдкрд░реАрдХреНрд╖рд╛ рдЙрдкрдпреЛрдЧреА рдиреЛрдЯреНрд╕ рдФрд░ рдСрдирд▓рд╛рдЗрди рдХреНрд╡рд┐рдЬрд╝ рдорд┐рд▓реЗрдВрдЧреЗред рдЕрдкрдиреЗ рдЬреНрдЮрд╛рди рдХрд╛ рдкрд░реАрдХреНрд╖рдг рдХрд░рдиреЗ рдФрд░ рдмреЛрд░реНрдб/рдкреНрд░рддрд┐рдпреЛрдЧреА рдкрд░реАрдХреНрд╖рд╛ рдореЗрдВ рд╢рдд-рдкреНрд░рддрд┐рд╢рдд рдЕрдВрдХ рдкреНрд░рд╛рдкреНрдд рдХрд░рдиреЗ рдХреЗ рд▓рд┐рдП рдиреАрдЪреЗ рджрд┐рдП рдЧрдП рдореЙрдХ рдЯреЗрд╕реНрдЯ рдореЗрдВ рдЕрд╡рд╢реНрдп рднрд╛рдЧ рд▓реЗрдВред
ЁЯСЙ рдЕрдзреНрдпрд╛рдп рдХрд╛ рд╕рд╛рд░рд╛рдВрд╢ (Summary)
Dear students, in this chapter, we will deeply study 1 extremely practical, powerful, and highly essential branch of physics that literally lights up our entire modern world: 'Alternating Current'. In the previous chapter, we studied electromagnetic induction and understood how 1 changing magnetic field generates 1 electric current. But the massive electricity that reaches our homes from giant power plants is not 1 simple steady direct current like the 1 we get from 1 small torch battery. It is an 'Alternating Current' or AC, whose exact magnitude changes continuously with time and whose strict direction reverses periodically. This highly efficient method of transmitting electrical energy over huge distances is the single biggest reason why we have affordable electricity in every single corner of the globe today.
Instead of just cramming complex mathematical formulas in closed books, if we logically connect physics with our daily life, it feels extremely magical. Have you ever thought deeply about how the high voltage electricity produced at massive dams exactly reaches our small house without losing all its energy in the extremely long transmission wires? Or why the charger of your mobile phone never explodes when you plug it directly into the 220 Volts wall socket? This is no magic trick, but it is 100 percent the scientific marvel of Alternating Current and Transformers. A transformer is 1 highly brilliant electrical device that actively works strictly on the principle of mutual induction to efficiently step up or step down the AC voltage. The massive power stations step up the voltage to 1000s of volts to successfully reduce energy loss during long-distance transmission, and the small transformer inside your phone charger effectively steps it down to just 5 Volts.
From the strict perspective of the upcoming NCERT and RBSE board exams, this specific chapter of physics is highly scoring and extremely important for your 100 percent success. In the board exams, not only direct theoretical questions are asked from this chapter, but excellent analytical, numerical, and derivation-based questions on the LCR series circuit, resonance condition, and the working principle of transformers definitely appear in the final exam paper every single year without fail. In this highly exciting journey, we will 1st study the exact mathematical representation of AC voltage and current. We will deeply understand the highly important concepts of peak value, mean value, and Root Mean Square (RMS) value of alternating current. The 220 Volts safely mentioned on our home appliances is actually the strict RMS value.
Moving 1 little further in the chapter, we will logically analyze the exact phase behavior of different electrical components like resistors, inductors, and capacitors when connected individually to 1 AC source. We will logically see how current exactly leads or lags the voltage by 1 phase angle of exactly 90 degrees in pure capacitors and pure inductors. After this, we will deeply study the most important topic of this entire chapter: the Series LCR Circuit. We will meticulously learn how to mathematically calculate its total impedance using phasor diagrams. Understanding the sharp 'Resonance' condition in 1 LCR circuit is 100 percent necessary, as this exact scientific principle is perfectly used to tune your radio or television to 1 specific broadcasting channel frequency.
Finally, we will deeply understand the crucial concepts of Power in AC circuits and the highly interesting phenomenon of 'Wattless Current'. To perfectly ensure your excellent and 100 percent strong preparation, we have meticulously selected and prepared completely accurate, high-level, and highly exam-useful objective questions (MCQs) from all these complex topics. By continuously practicing again and again, you will surely learn critical time management and massively increase your speed of solving complex numerical questions without making even 1 single mistake.
Feature: This is 1 3-Level based unique quiz. To unlock the next level (Level 2 and 3), students must score at least 70% in the current level, making their board exam preparation 100% strong.
рдорд╣рддреНрд╡рдкреВрд░реНрдг рдкреНрд░рд╢реНрди (Important Questions)
PDF рдбрд╛рдЙрдирд▓реЛрдб рдХрд░реЗрдВрдЕрдзреНрдпрд╛рдп рдХреЗ рд╕рднреА рдкреНрд░рд╢реНрди (Revision Notes)
*рдиреЛрдЯ: рдпрд╣ рд╕реЗрдХреНрд╢рди рд░рд┐рд╡реАрдЬрди рдХреЗ рд▓рд┐рдП рд╣реИред рдЕрдкрдирд╛ рдЬреНрдЮрд╛рди рдкрд░рдЦрдиреЗ рдХреЗ рд▓рд┐рдП рдКрдкрд░ рджрд┐рдП рдЧрдП рдХреНрд╡рд┐рдЬрд╝ рдореЗрдВ рднрд╛рдЧ рд▓реЗрдВред
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Relation between peak value (IтВА) and RMS value of AC?
A) Irms = IтВА/тИЪ2 | B) Irms = IтВА/2 | C) Irms = тИЪ2IтВА | D) Irms = 2IтВА -
Frequency of AC used in Indian households?
A) 100 Hz | B) 60 Hz | C) 50 Hz | D) 0 Hz -
Transformer works on which current?
A) Only DC | B) Only AC | C) Both | D) None -
Power Factor in a pure resistive AC circuit is?
A) 0 | B) 1 | C) 0.5 | D) Infinity -
Frequency of Direct Current (DC) is?
A) 50 Hz | B) 60 Hz | C) Zero | D) Infinity -
Formula for Inductive Reactance (X_L)?
A) ╧ЙL | B) 1/╧ЙL | C) L/╧Й | D) ╧Й┬▓L -
Unit of Capacitive Reactance (X_C)?
A) Henry | B) Farad | C) Ohm | D) Volt -
In LCR circuit, Impedance is denoted by?
A) R | B) X | C) Z | D) Y -
In resonance, relation between X_L and X_C is?
A) X_L > X_C | B) X_L < X_C | C) X_L = X_C | D) X_L = 0 -
Step-up Transformer increases?
A) Current | B) Voltage | C) Power | D) Frequency -
In Step-down Transformer, number of secondary turns (Ns):
A) Ns > Np | B) Ns < Np | C) Ns = Np | D) Zero -
Which value of AC does an ammeter measure?
A) Peak | B) Average | C) RMS | D) Zero -
Maximum value of Power Factor can be?
A) 0 | B) 1 | C) 100 | D) 0.5 -
Transformer core is made of:
A) Steel | B) Soft Iron | C) Copper | D) Aluminum -
Use of Rectifier is:
A) Convert AC to DC | B) Convert DC to AC | C) Increase voltage | D) None -
Average value of AC for one full cycle is:
A) IтВА/тИЪ2 | B) 2IтВА/╧А | C) Zero | D) Peak -
In pure inductive circuit, current ________ voltage:
A) Leads by 90┬░ | B) Lags by 90┬░ | C) In phase | D) Lags by 180┬░ -
In pure capacitive circuit, current ________ voltage:
A) Leads by 90┬░ | B) Lags by 90┬░ | C) In phase | D) Leads by 45┬░ -
Wattless current is found in?
A) Pure resistor | B) Pure inductor or capacitor | C) LCR circuit | D) DC circuit -
Impedance (Z) at resonance is:
A) Maximum | B) Minimum (Z=R) | C) Infinite | D) Zero -
Choke coil reduces current:
A) Without power loss | B) With high power loss | C) Only in DC | D) None -
Cause of energy loss in transformer:
A) Eddy currents | B) Copper loss | C) Hysteresis loss | D) All of the above -
Quality Factor (Q-factor) measures sharpness of?
A) Current | B) Resonance | C) Voltage | D) Power -
X_C varies with frequency (f) as?
A) X_C тИЭ f | B) X_C тИЭ 1/f | C) X_C тИЭ f┬▓ | D) Independent -
X_L varies with frequency (f) as?
A) X_L тИЭ f | B) X_L тИЭ 1/f | C) Constant | D) Zero -
Formula for Power Factor (cos╧Ж) is:
A) R/Z | B) Z/R | C) X/R | D) R/X -
Reactance (X_C) of capacitor for DC circuit is:
A) Zero | B) Infinite | C) Constant | D) 1 Ohm -
Energy transfer in LC oscillations is between:
A) Electric and Magnetic fields | B) Only electric field | C) Only heat | D) None -
Efficiency of a transformer is usually:
A) 10% | B) 50% | C) 90-99% | D) 100% -
Phase between voltage and current in LCR depends on:
A) Only R | B) Only L | C) Values of R, L and C | D) Not on frequency -
If peak AC voltage is 311V, RMS value is?
A) 311V | B) 220V | C) 110V | D) 440V -
Z of series 10╬й resistor and 10╬й inductor is?
A) 20╬й | B) 14.14╬й | C) 10╬й | D) Zero -
Formula for Resonant Frequency (fr) is?
A) 1 / (2╧АтИЪLC) | B) 2╧АтИЪLC | C) тИЪLC / 2╧А | D) 1 / (LC) -
Time for 60Hz AC to reach peak from zero?
A) 1/60 s | B) 1/120 s | C) 1/240 s | D) 1/480 s -
Reactance X_L of 0.1H coil at 50Hz?
A) 31.4╬й | B) 314╬й | C) 10╬й | D) 50╬й -
Np=100, Ns=200. If Vp=10V, then Vs is?
A) 5V | B) 20V | C) 10V | D) 40V -
Irms=5A, Vrms=200V, cos╧Ж=0.8. Average power is?
A) 1000W | B) 800W | C) 400W | D) 1250W -
X_C of 100┬╡F capacitor at 50Hz?
A) 31.8╬й | B) 318╬й | C) 10╬й | D) 63.6╬й -
I = 10 sin(100╧Аt). Frequency is?
A) 100 Hz | B) 50 Hz | C) 25 Hz | D) 10 Hz -
Average power loss in pure inductor circuit is:
A) VI | B) V┬▓I | C) Zero | D) 1/2 VI -
Current at 'resonance' in series LCR is:
A) Minimum | B) Maximum | C) Zero | D) Constant -
Turns ratio k=2. If Ip=4A, then Is is?
A) 8A | B) 2A | C) 4A | D) 1A -
Hot-wire ammeter is based on?
A) Magnetic effect | B) Heating effect | C) Chemical effect | D) None -
Circuit with zero power factor is:
A) Pure resistive | B) Wattless | C) High power | D) DC -
╧Йr for L=2H, C=32┬╡F is:
A) 125 rad/s | B) 250 rad/s | C) 100 rad/s | D) 500 rad/s
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