Quiz-18 ALTERNATING CURRENT

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ALTERNATING CURRENT Quiz-18

Dear Readers,

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background. Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced. .

Q1. An alternating voltage (in volt) given by V=200√2 sin⁡ (100t) is connected to 1μF capacitor through an AC ammeter. The reading of the ammeter will be

•  10 mA
•  20 m A
•  40 mA
•  80 mA

Solution
It is a fact.

Q2. In an AC circuit, V and I are given by V=150 sin⁡ (150t) volt and I=150 sin⁡ (150t+π/3)  amp. The power dissipated in the circuit is

•  Zero
•  5625 W
•  150 W
•  106 W

Solution
Power P=1/2 V₀ I₀ cos⁡ϕ 

=0.5×150×150× cos⁡ 60°

=22500/4 =5625 W

Q3. The resonance frequency of the tank circuit of an oscillator when L=10/π² mH and C=0.04 μF are connected in parallel is

•  250 kHz
•  25 kHz
•  2.5 kHz
•  25 MHz

Solution
In parallel resonant circuit, resonance frequency 

Q4. The process by which ac is converted into dc is known as

•  Purification
•  Amplification
•  Rectification
•  Current amplification

Solution
It is a fact.

Q5. In the adjoining figure the impedance of the circuit will be 

•  120 ohm
•  50 ohm
•  60 ohm
•  90 ohm

Solution
i_L = 90/30 = 3A 

i_C = 90/20 = 4.5 

A Net current through circuit i = i_C-i_L=1.5 A 

∴ Z = V/i = 90/1.5 = 60Ω

Q6. An emf is 15 V is applied in a circuit coil containing 5 H inductance and 10 Ω resistance. The ratio of currents at time t=∞ and t=1 s is

•  e^1/2/(e^1/2- 1)
•  e²/(e²-1)
• 1-e^-1
•  e^-1

Solution
Here, i=i₀ at t=∞.Let i be the current at t = 1 s 

From i=i₀ (1-e^{-R/L t}) = i₀ (1-e^-10/5×1)

=i₀ (1-1/e²) 

∴ i₀/i= e²/(e²-1)

Q7. A transformer is used to light 140 W, 24 V lamp from 240 V AC mains. The current in the mains is 0.7 A. The efficiency of transformer is nearest to

•  90%
•  80%
•  70%
•  60%

Solution
P_i=240 × 0.7=168 W, P₀=140 W 

η = P₀/P_i ×100=140/168×100 ≈80%

Q8. Eddy current are produced when

•  A metal is kept in varying magnetic field
•  A metal is kept in steady magnetic field
•  A circular coil is placed in a magnetic field
•  Through a circular coil, current is passed

Solution
Eddy currents are produced when a metal is kept in a varying magnetic field.

Q9. An inductive circuit contains a resistance of 10 ohm and an inductance of 2.0 henry. If an ac voltage of 120 volt and frequency of 60 Hz is applied to this circuit, the current in the circuit would be nearly

•  0.32 amp
•  0.16 amp
•  0.48 amp
•  0.80 amp

Solution

Q10. The instantaneous values of current and voltage in an ac circuit are i=100 sin ⁡314 t amp and e=200 in (314 t+π/3)V respectively. If the resistance is 1Ω, then the reactance of the circuit will be

•  -200√3 Ω
•  √3 Ω
•  -200√3 Ω
•  100√3 Ω

Solution
V₀=i₀ Z⇒200=100 Z ⇒Z=2Ω 

Also Z²=R²+X_L²⇒(2)²=(1)²+X_L²⇒X_L=√3 Ω