Question 11 Mark
Name the logic gates marked P and Q in the given logic circuit.
Answer
View full question & answer→- P = NOT gate.
- Q = OR gate.
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38 questions · timed · auto-graded
Name the logic gates marked P and Q in the given logic circuit.
Question 21 Mark
Two wires one of copper and other of manganin have same resistance and equal length. Which wire is thicker and why?
Answer
$\text{R}_{c} = \rho_{c}\frac{l}{\text{A}_{c}} ; \text{R}_{m} = \rho_{m}\frac{l}{\text{A}_{m}}.\text{ since } \rho_{m} > \rho_{c}\therefore \text{A}_{m} > \text{A}_{c}$
View full question & answer→- Manganin.
- $\text{R} = \frac{pl}{\text{A}^{.}}$ As $\rho$ increases A also increases.
$\text{R}_{c} = \rho_{c}\frac{l}{\text{A}_{c}} ; \text{R}_{m} = \rho_{m}\frac{l}{\text{A}_{m}}.\text{ since } \rho_{m} > \rho_{c}\therefore \text{A}_{m} > \text{A}_{c}$
Question 31 Mark
Define the term relaxation time' in a conductor.
Answer
View full question & answer→Def: The average time, between successive collisions of electrons, (in a conductor) is known as relaxation time.
Question 41 Mark
The power factor of an a.c. circuit is 0.5. What is the phase difference between voltage and current in the circuit?
Answer
View full question & answer→Phase angle = $60^\circ$.
Question 51 Mark
What is the amount of work done in moving a point charge Q around a circular arc of radius ‘r' at the centre of which another point charge ‘q' is located?
Answer
View full question & answer→Zero/No work done/None.
Question 61 Mark
Define mobility of a charge carrier. What is its relation with relaxation time?
Answer
View full question & answer→Drift velocity per unit field
$(\mu_{m} = u_{d}\big/\text{E})$
$\mu_{n}\propto\tau$.
$(\mu_{m} = u_{d}\big/\text{E})$
$\mu_{n}\propto\tau$.
Question 71 Mark
What can be the cause of helical motion of a charged particle?
Answer
View full question & answer→Charged particle moves inclined to the magnetic field (angle between $\overrightarrow{\vartheta}$ and $\overrightarrow{\text{B}}$ is neither $\frac{\pi}{2}$ nor 0).
(component of $\overrightarrow{\vartheta}$, parallel to $\overrightarrow{\text{B}}$ , is not zero.)
(component of $\overrightarrow{\vartheta}$, parallel to $\overrightarrow{\text{B}}$ , is not zero.)
Question 81 Mark
Why can't we see clearly through fog? Name the phenomenon responsible for it.
Answer
View full question & answer→(Some) light gets deviated/scattered/absorbed.
Scattering of light.
Scattering of light.
Question 91 Mark
Two signals A and B are used as inputs of a NOR gate. Draw the output wave form.
Question 101 Mark
The variation of potential V with length l in case of two potentiometers wires P and Q is as shown. Which one of these will you prefer comparing emfs of two primary cells and why?
Answer
View full question & answer→Potentiometer ‘Q’ will be preferred
Reason: $\text{Sensitivity}\propto\frac{1}{\text{potential gradient (k)}}$
Since potential gradient is less, sensitivity is more.
Reason: $\text{Sensitivity}\propto\frac{1}{\text{potential gradient (k)}}$
Since potential gradient is less, sensitivity is more.
Question 111 Mark
Why is the use of a.c. voltage preferred over d.c. voltage? Give two reasons.
Answer
View full question & answer→Any two of the following reasons:
- AC can be transmitted with much lower energy losses as compared to DC.
- AC voltage can be adjusted (stepped up or stepped down) as per requirement.
- AC current in a circuit can be controlled using (almost) wattless devices like the choke coil.
- AC is easier to generate.
Question 121 Mark
In which situation is there a displacement current but no conduction current?
Answer
View full question & answer→Between plates of capacitor during charging/discharging.
Alternate Answer
In the region of time-varying electric field.
Alternate Answer
In the region of time-varying electric field.
Question 131 Mark
A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. What are the frequencies of the side bands produced?
Answer
View full question & answer→$\text{V}_{side bands} = \text{V}_{c}\pm\text{u}_{m}$
= 2005 kHz ; 1995 kHz.
= 2005 kHz ; 1995 kHz.
Question 141 Mark
Define the term conductivity of a conductor. On what factors does it depend?
Answer
View full question & answer→Conductivity of a conductor is the current flowing per unit area per unit electric field applied.
Alternate Answer
conductivity $\sigma = \frac{j}{\text{E}}$
Depends upon number density i.e. nature of material, and relaxation time i.e. temperature.
Alternate Answer
conductivity $\sigma = \frac{j}{\text{E}}$
Depends upon number density i.e. nature of material, and relaxation time i.e. temperature.
Question 151 Mark
The variation of potential V with length l in case of two potentiometers wires P and Q is as shown. Which one of these will you prefer comparing emfs of two primary cells and why?
Answer
View full question & answer→Potentiometer ‘Q’ will be preferred
Reason: $\text{Sensitivity}\propto\frac{1}{\text{potential gradient (k)}}$
Since potential gradient is less, sensitivity is more.
Reason: $\text{Sensitivity}\propto\frac{1}{\text{potential gradient (k)}}$
Since potential gradient is less, sensitivity is more.
Question 161 Mark
Explain why current flows through an ideal capacitor when it is connected to an a.c. Source but not when it is connected to a do. Source in a steady state.
Answer
View full question & answer→For a.c. source, circuit is complete due to the presence of displacement current in the capacitor. For steady dc, there is no displacement current, therefore, circuit is not complete.
Alternate Answer
[Capacitive reactance $\text{X}_{c} =\frac{1}{2\pi\text{fC}} = \frac{1}{\omega\text{t}}$
So, capacitor allows easy path for a.c. Source. For d.c, f= 0, so Xc = infinity, So capacitor blocks d.c].
Alternate Answer
[Capacitive reactance $\text{X}_{c} =\frac{1}{2\pi\text{fC}} = \frac{1}{\omega\text{t}}$
So, capacitor allows easy path for a.c. Source. For d.c, f= 0, so Xc = infinity, So capacitor blocks d.c].
Question 171 Mark
An a.c. source of voltage $\text{V} = \text{V}_{o} \sin \omega \text{t}$ is connected to an ideal inductor. Draw graphs of voltage V and current i versus $\omega\text{t}.$
Answer
Graph of V.
Graph of I.
View full question & answer→Graph of V.
Graph of I.
Question 181 Mark
The instantaneous current and voltage of an a.c. circuit are given by
i = 10 sin 300t A and v = 200 sin 300t V
What is the power dissipation in the circuit?
i = 10 sin 300t A and v = 200 sin 300t V
What is the power dissipation in the circuit?
Answer
View full question & answer→$\text{P} = \frac{1}{2}\text{E}_{0}\text{I}_{0}$
Power dissipated = 1000 W or 1 kW.
Power dissipated = 1000 W or 1 kW.
Question 191 Mark
In a series LCR circuit, the voltages across an inductor, a capacitor and a resistor are 30 V, 30 V and 60 V respectively. What is the phase difference between the applied voltage and the current in the circuit?
Answer
View full question & answer→Applied Voltage and current are in the same phase.Alternate Answer
$\theta = 0 $ or simply zero.Alternate Answer
tan $\theta = \frac{\text{V}_{L} -\text{V}_{c}}{\text{V}_{R}} = 0 $.Alternate Answer
$\tan \theta = 0 $.
$\theta = 0 $ or simply zero.Alternate Answer
tan $\theta = \frac{\text{V}_{L} -\text{V}_{c}}{\text{V}_{R}} = 0 $.Alternate Answer
$\tan \theta = 0 $.
Question 201 Mark
Define capacitor reactance. Write its S.I. units.
Answer
View full question & answer→It is defined as the opposition to the flow of current in AC circuits offered by a capacitor.
Alternate Answer
$\text{X}_{c} = \frac{1}{\omega\text{c}}$
S.l unit: ohm.
Alternate Answer
$\text{X}_{c} = \frac{1}{\omega\text{c}}$
S.l unit: ohm.
Question 211 Mark
Define ‘quality factor’ of resonance in series LCR circuit. What is its SI unit?
Answer
View full question & answer→Quality factor $\text{Q} = \frac{\omega_o}{2\Delta\omega} , $
Alternate Answer
Quality factor $\text{Q} = \frac{\omega_o\text{L}}{\text{R}} , $
Alternate Answer
It gives the sharpness of the resonance circuit.]
It has no unit.
Alternate Answer
Quality factor $\text{Q} = \frac{\omega_o\text{L}}{\text{R}} , $
Alternate Answer
It gives the sharpness of the resonance circuit.]
It has no unit.
Question 221 Mark
Define the term 'wattless current'.
Answer
View full question & answer→Current flowing in a circuit without any net dissipation of power, is called wattless current.
Question 231 Mark
When an AC source is connected to a capacitor there is a steady-state current in the circuit. Does it mean thatthe charges jump from one plate to the other to complete the circuit?
Answer
View full question & answer→No.
Question 241 Mark
An AC source is connected to a capacitor. Will the rms current increase, decrease or remain constant if a dielectric slab is inserted into the capacitor?
Answer
View full question & answer→$\text{X}_\text{c}=\frac{1}{\omega\text{C}}$ as slab is introduced $C$ increases and $X_C$ decreases so current increases.
Question 251 Mark
Can a hot-wire ammeter be used to measure a direct current having a constant value? Do we have to change the graduations?
Answer
View full question & answer→Yes, in this case $\mathrm{I}_{\mathrm{rms}}$ value will be same as the DC current.
Question 261 Mark
What is the reactance of a capacitor connected to a constant DC source?
Answer
View full question & answer→$\text{X}_\text{c}=\frac{1}{\omega\text{C}}$
As,
$\omega=0$
For,
$\text{DC},\text{X}_\text{c}=\infty.$
As,
$\omega=0$
For,
$\text{DC},\text{X}_\text{c}=\infty.$
Question 271 Mark
In a circuit containing a capacitor and an AC source the current is zero at the. stant the source voltage is maximum. Is it consistent with Ohm's law?
Answer
View full question & answer→Ohm's law is valid for resistance.
Question 281 Mark
Can the peak voltage across the inductor be greater than the peak voltage of the source in an LCR circuit?
Answer
View full question & answer→Yes,
Consider example below:
Consider example below:
Question 291 Mark
A current $\text{i}_1=\text{i}_0\sin\omega\text{t}$ passes through a resistor of resistance R. How much thermal energy is produced in one time period? A current $\text{i}_2=-\text{i}_0\sin\omega\text{t}$ passes through the resistor. How much thermal energy is produced in one time period? If $i_1$, and $i_2$ both pass through the resistor simultaneously, how much thermal energy is produced? Is the principle of superposition obeyed in this case?
Answer
View full question & answer→$\text{I}_\text{rms}^{2}\times\text{R}\times\frac{2\pi}{\omega}$ from definition of rms current.
$i_1$, and $i_2$ both pass through the resistor simultaneously, and same thermal energy is produced.
Similary, the principle of superposition obeyed in this case zero.
$i_1$, and $i_2$ both pass through the resistor simultaneously, and same thermal energy is produced.
Similary, the principle of superposition obeyed in this case zero.
Question 301 Mark
What is the phase difference between voltage and current in a LCR series circuit at resonance?
Answer
View full question & answer→At resonance voltage and current are in the same phase, i.e., phase difference between voltage and current at resonance is zero.
Question 311 Mark
Is energy produced when a transformer steps up the voltage?
Answer
View full question & answer→No, as voltage increases current decreases. Hence, if efficiency is 100% power will be same.
Question 321 Mark
When the frequency of the AC source in an LCR circuit equals the resonant frequency, the reactance of the circuit is zero. Does it mean that there is no current through the inductor or the capacitor?
Answer
View full question & answer→There is current but the potential difference across inductor and capacitor cancel each other.
Question 331 Mark
Can you, have an AG series circuit in which there is. a phase difference of 180° between the emf and the current? 120°?
Answer
View full question & answer→No.
Question 341 Mark
State which of the two, the capacitor or an inductor, tends to become a SHORT when the frequency of the applied alternating voltage has a very high value.
Answer
View full question & answer→The capacitor $\text{X}_{\text{C}}=\frac{1}{\omega{\text{C}}}=\frac{1}{2\pi\text{vC}}$
When $\text{v}\rightarrow\infty(\text{very high})$
$\text{X}_{\text{C}}=0$
When $\text{v}\rightarrow\infty(\text{very high})$
$\text{X}_{\text{C}}=0$
Question 351 Mark
Two alternating currents are given by, $\text{i}_\text{i}=\text{i}_0\sin\omega\text{t}$ and $\text{i}_\text{i}=\text{i}_0\sin\Big(\omega\text{t}+\frac{\pi}{3}\Big)$ Will the rms values of the currents be equal or different?
Answer
View full question & answer→$\mathrm{I}_{\mathrm{rms}}$ will be equal because in a complete cycle heat dissipated will be equal for both.
Question 361 Mark
In India, Domestic power supply is at 220V, 50Hz; while in USA it is 110V, 50Hz. Give one advantage and one disadvantage of 220V supply over 110V supply.
Answer
View full question & answer→Advantage: Line loss is low.
Disadvantage: High voltage is dangerous.
Disadvantage: High voltage is dangerous.
Question 371 Mark
A pure inductor of $25.0 mH$ is connected to a source of $220 V$. Find the inductive reactance and rms current in the circuit if the frequency of the source is $50 Hz$.
Answer
View full question & answer→The inductive reactance,
$
\begin{aligned}
X_L & =2 \pi v L=2 \times 3.14 \times 50 \times 25 \times 10^{-3} \Omega \\
& =7.85 \Omega
\end{aligned}
$
The rms current in the circuit is
$
I=\frac{V}{X_L}=\frac{220 V }{7.85 \Omega}=28 A
$
$
\begin{aligned}
X_L & =2 \pi v L=2 \times 3.14 \times 50 \times 25 \times 10^{-3} \Omega \\
& =7.85 \Omega
\end{aligned}
$
The rms current in the circuit is
$
I=\frac{V}{X_L}=\frac{220 V }{7.85 \Omega}=28 A
$
Question 381 Mark
At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?
Answer
View full question & answer→The metal detector works on the principle of resonance in ac circuits. When you walk through a metal detector, you are, in fact, walking through a coil of many turns. The coil is connected to a capacitor tuned so that the circuit is in resonance. When you walk through with metal in your pocket, the impedance of the circuit changes - resulting in significant change in current in the circuit. This change in current is detected and the electronic circuitry causes a sound to be emitted as an alarm.