Alternating Current - Quiz 2

ALTERNATING CURRENT QUIZ-1

Dear Readers,

JEE Advanced Physics Syllabus can be referred by the IIT aspirants to get a detailed list of all topics that are important in cracking the entrance examination. JEE Advanced syllabus for Physics has been designed in such a way that it offers very practical and application-based learning to further make it easier for students to understand every concept or topic by correlating it with day-to-day experiences. In comparison to the other two subjects, the syllabus of JEE Advanced for physics is developed in such a way so as to test the deep understanding and application of concepts.

Q1. In the circuit shown in Fig, R is a pure resistor, L is an inductor of negligible resistance (as compared to R), S is a 100 V, 50 Hz ac source of negligible resistance. With either key K₁ alone or K₂ alone closed, the current isI₀. If the source is changed to 100 V, 100 Hz the current with K₁ alone closed and with K₂ alone closed will be respectively

•  I₀,I₂/2
•  I₀,2I₀
•  2I₀,I₀;
•  2I₀,I₀/2

Solution

(a) Current remains unchanged in R. However, it becomes half in L, because reactance is doubled on doubling the frequency.

Q2. The circuit given in Fig has a resistance less choke coil L and a resistance R. The voltage across R and L are given in Fig. The virtual of the applied voltage is?

•  100 V
•  200 V
•  300 V
•  400 V

Solution

(b) E_v=√(120²+160² )=200 V

Q3. If i₁=3 sin⁡ωt and i₂=4 cos⁡ωt, then i₃ is

•  5 sin⁡(ωt+53^°)
•  5 sin⁡(ωt+37^°)
•  5 sin⁡(ωt+45^°)
•  5 sin⁡(ωt+53^°)

Solution

Q4. A coil has an inductance of 0.7 H and is joined is series with a resistance of 220 Ω. When an alternating emf of 220 V at 50 cps is applied to it, then the wattles component of the current in the circuit is (take 0.7π=2.2)

•  5 A
•  0.5 A
•  0.7 A
•  7 A

Solution

Q5. In the above question, the average value of voltage (V) in one time period will be

•  V₀/√3
•  V₀/2
•  V₀/√2
•  0

Solution

Q6. A series R-C circuit is connected to AC Voltage source. Consider two cases: A when C is without a dielectric medium and B when C is filled with dielectric of constant 4. The current I_R through the resistor and voltage V_c across the capacitor are compared in the two cases. Which of the following is/are true?

•  I_R^A>I_R^B
•  I_R^A < I_R^B
•  V_C^A>V_C^B
•  V_C^A < V_c^B

Solution

Q7. A transmitter transmits at a wavelength of 300 m. A condenser of capacitance 2.4 μ F is being used. The value of the inductance for the resonant circuit is approximately

•  10^-4 H
•  10^-6 H
•  10^-8 H
•  10^-10 H

Solution

Q8. If the total charge stored in the LC circuit is Q₀, then for t≥0

•  The charge on the capacitor is Q=Q₀ cos⁡(π/2+t/√LC)
•  The charge on the capacitor is Q=Q₀ cos⁡(π/2-t/√LC)
•  The charge on the capacitor is Q=-LC (d² Q)/(dt²)
•  The charge on the capacitor is Q=1/√LC (d² Q)/(dt²)

Solution

(c)

Q9. A 4μF capacitor, a resistance of 2.5 mΩ is in series with 12 V battery. Find the the time after which the potential difference across the capacitor is 3 times the potential difference across the resistor. [Given ln (2)=0.693]

•  13.86s
•  6.93s
•  7s
•  14s

Solution

Q10. In an R-C circuit while charging, the graph of lnI versus time is as shown by the dotted line in the adjoining diagram where I is the current. When the value of the resistance is doubled, which of the solid curves best represents the variation of ln I versus time?

•  P
•  Q
•  R
•  S

Solution