Electric Generator

Q.

Explain the working of a dynamo.

Q.

A transformers core is laminated to minimize weight.

1. Flux leakage

2. Output power

3. Hysteresis

4. Copper loss

5. Eddy current

Q. The number of turns in the coil of an ac­ generator is 5000 and the area of the coil is
$0.25m^2$. The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2 W/$m^2$. The peak value of the emf generated is nearly

1. 786 kV
2. 440 kV
3. 157.1 kV
4. 220 kV

Q.

Two concentric circular coils, $C_1$ and $C_2$, are placed in the XY plane. $C_1$ has $500turns$, and a radius of $1cm$. $C_2$ has $200turns$ and a radius of $20cm$. $C_2$ carries a time-dependent current $I\left(t\right)=\left(5t^2-2t+3\right)A$ where $t$ is in $s$. The emf induced in $C_1$ (in mV), at the instant $t=1s$ is $\frac{4}{x}$. The value of $x$ is ________.

Q. The potential difference V and current I flowing through an instrument in an AC circuit are given by $V=5cos\omega t$ volt and $i=2sin\omega t$ ampere respectively. Then the power dissipated in the instrument is

1. 0 W
2. 2.5 W
3. 5 W
4. 10 W.

Q.

A small-signal voltage $V\left(t\right)=V_o\sin \omega t$ is applied across an ideal capacitor C

1. Current I (t) is in phase with voltage V(t).

2. Over a full cycle the capacitor C does not consume any energy from the voltage source.

3. Current I(t), lags voltage V(t) by 90 degrees.

4. Current I(t) leads voltage V(t) by 180 degrees.

Q. An electric appliance supplies $6000\text{J/min}$ of heat to the system. If the system delivers power of $90\text{W}$, how long would it take to increase its internal energy by $2.5\times {10}^3\text{J}$?

1. $2.5\times {10}^1\text{s}$
   
2. $4.1\times {10}^1\text{s}$
   
3. $2.4\times {10}^3\text{s}$
   
4. $2.5\times {10}^2\text{s}$
   

Q. A flexible wire bent in the form of a circle is placed in a uniform magnetic field perpendicular to the plane of the coil. The radius of the coil changes as shown in the figure.

The graph of magnitude of induced emf in the coil is represented by

1. 
2. 
3. 
4. 

Q.

Lap winding is preferred for which type of machines?

1. Low current and low voltage

2. High current and high voltage

3. High current and low voltage

4. Low current and high voltage

Q. Assertion $\left(A\right)$: In series $\text{LCR}$ circuit resonance can take place.

Reason $\left(R\right)$: Resonance takes place iff inductive reactance and capacitive reactances are equal with phase difference ${180}^{\circ }.$

1. Both $\left(A\right)$ and $\left(R\right)$ are true, and $\left(R\right)$ is the correct explanation of $\left(A\right)$
2. Both $\left(A\right)$ and $\left(R\right)$ are true, but $\left(R\right)$ is not the correct explanation of $\left(A\right)$
3. $\left(A\right)$ is true but $\left(R\right)$ is false
4. $\left(A\right)$ is false but $\left(R\right)$ is true

Q. The current in a certain circuit varies with time, as shown in the figure.

1. The average current from $t=0$ to $t=2\text{s}$ is $2.5\text{A}$
   
2. The average current for a full cycle is zero.
3. The rms current from $t=0$ to $t=4\text{s}$ is $\frac{5}{\sqrt{2}}\text{A}$
   
4. The rms current from $t=0$ to $t=4\text{s}$ is $\frac{5}{\sqrt{6}}\text{A}$
   
   

Q. According to the modified Ampere's circuital law ($i_D=$ displacement current)

1. $\oint \overrightarrow{B}\cdot \overrightarrow{dl}={\mu }_0(i_C+{\epsilon }_0\frac{d{\varphi }_E}{dt})$
2. $\oint \overrightarrow{B}\cdot \overrightarrow{dl}={\mu }_0{\epsilon }_0\frac{d{\varphi }_E}{dt}$
3. $\oint \overrightarrow{B}\cdot \overrightarrow{dl}={\mu }_0{i}_C$
4. $\oint \overrightarrow{B}\cdot \overrightarrow{dl}={\mu }_0(i_C\frac{d{\varphi }_E}{dt}+i_D)$

Q. Which component does not belong to AC generator?

1. Starter
2. Rotor
3. Magnetic field
4. Slip rings

Q. The current decaying in a circuit has a function $i=I_0{e}^{-t/\tau }$ where $\tau$ is the time constant of the circuit. Find $rms$ value of the current for the period $t=0\text{to}t=\tau$.

1. $\frac{I_0}{\sqrt{2}}\sqrt{1-\frac{1}{e^2}}$
2. $\frac{I_0}{\sqrt{2}}\sqrt{1+\frac{1}{e^2}}$
3. $I_0\sqrt{1-e^2}$
4. $I_0\sqrt{1+e^2}$

Q. A single solar cell of dimension $(10\text{cm}\times 10\text{cm})$ produces a voltage of $0.5\text{V}$ and current $2.5\text{A}$. The intensity of light absorbs by cell is $800{\text{W/m}}^2$. The efficiency of cell is -

1. $15.6\%$
2. $24\%$
3. $12.3\%$
4. $10.2\%$

Q. A generator produces a voltage of v = 240 sin 120t volt, where ‘t’ is the time in seconds. The frequency and rms voltages are

1. $19Hz170V$
2. $60Hz,240V$
3. $19Hz,20V$
4. $75Hz,40V$

Q. A moving coil galvanometer shows deflection of 100 divisions when 20 mA current is passed through it. If the resistance of the galvanometer coil is 50 ohm , find the voltage sensitivity of galvanometer

Q. The number of turns in the coil of an ac­ generator is 5000 and the area of the coil is
$0.25m^2$. The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2 W/$m^2$. The peak value of the emf generated is nearly

1. 786 kV
2. 440 kV
3. 220 kV
4. 157.1 kV

Q. A circuit contains a resistance $R$ and an inductance $L$ in series. An alternating voltage $V=V_0\sin \omega t$ is applied across it. The currents in $R$ and $L$ respectively will be ($I_0$ is the peak current)

1. $I_R=I_0\cos \omega t,I_L=I_0\cos \omega t$
2. $I_R=I_0\sin \omega t,I_L=I_0\cos \omega t$
3. $I_R=I_0\sin \omega t,I_L=-I_0\cos \omega t$
4. $I_R=I_L=I_0\sin \omega t$

Q. the electric field in an electromagnetic wave was found to oscillate with an amplitude of 36v/m. the amplitude of the oscillating magnetic field is

Q. In a series $LC$ circuit, the applied voltage is $V_0$. If frequency is very low, then the voltage drop across the inductor $V_L$ and capacitor $V_C$ are

1. $V_L=\frac{V_0}{2},V_C=\frac{V_0}{2}$
2. $V_L=0,V_C=V_0$
3. $V_L=V_0,V_C=0$
4. $V_L=0,V_C=\frac{V_0}{2}$

Q.

What energy transformation takes place in an a.c. generator ?

Q. An AC generator consists of a coil of $50$ turns and an area $2.5{\text{m}}^2$ rotating at an angular speed of $60\text{rad/s}$ in a uniform magnetic field of $0.3\text{T}$ between two fixed pole pieces. What is the magnetic flux through the coil, when the current is maximum?

1. $425\text{Wb}$
2. $334\text{Wb}$
3. $501\text{Wb}$
4. Zero

Q. WHICH IS MORE ACCURATE FOR 6.28 CM 1. 5.99 CM 2. 6.00 CM 3. 6.56 CM 4. 6 CM

Q. An alternating current is given by the following equation, $I=3\sqrt{2}\sin (100\pi t+\frac{\pi }{4})$
Find the frequency and $rms$ value of the current over a full cycle.

1. $50\text{Hz},3\text{A}$
2. $50\text{Hz},3\sqrt{2}\text{A}$
3. $50\text{Hz},\frac{3}{\sqrt{2}}\text{A}$
4. $25\text{Hz},3\text{A}$

Q. Dynamo is a type of

1. Electrical generator
2. Electrical motor
3. Mechanical motor
4. Mechanical generator

Q.

The Maximum Efficiency of a Full-Wave Rectifier is

1. 100%

2. 25.20%

3. 42.2%

4. 81.2%

Q. Find the average current for the time interval $t=0$ to $t=5\text{s}$ if the current is given by, $i=(2t+1)\text{A}$.

1. $2\text{A}$
2. $4\text{A}$
3. $6\text{A}$
4. $8\text{A}$

Q.

A device which converts electrical energy into mechanical energy is called:

1. Electric generator

2. Electric motor

3. Electric conductor

4. Electric transformer

Q.

What type of current is produced by an electric generator?