Alternating Current Test

Result

Alternating Current Test - 81

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Question 1
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A $$50Hz$$ alternating current of peak value $$1$$ ampere flows through the primary coil of a transformer. If the mutual inductance between the primary and secondary be $$1.5$$ henry, then the mean value of the induced voltage is:

A
$$75$$ volt

B
$$150$$ volt

C
$$225$$ volt

D
$$300$$ volt

Solution
Question 2
1 / -0

In the circuit shown in figure. the a.c. source gives a voltage V = 20 $$\cos ( 200 \pi + 1 )$$ The reading of vulimeter and amineter will be

A
$$0 \mathrm { V } , 0.47 \mathrm { A }$$

B
$$5.6 \mathrm { V } , 1.4 \mathrm { A }$$

C
$$0 \mathrm { V } , 1.4 \mathrm { A }$$

D
$$\frac { 2 \mathrm { R } } { ( 2 \mu - 1 ) }$$

Solution

$$\begin{array}{l} Z=\sqrt { { { \left( R \right) }^{ 2 } }+{ { \left( { { X_{ L } }-{ X_{ C } } } \right) }^{ 2 } } } \\ R=10\Omega ,\, \, { X_{ L } }=wL=2000\times 5\times { 10^{ -3 } }=10\Omega \\ { X_{ C } }=\dfrac { 1 }{ { wC } } =\dfrac { 1 }{ { 2000\times 50\times { { 10 }^{ -6 } } } } =10\Omega \\ i.e,\, \, Z=10\Omega \\ \max imum\, \, current\, \, { i_{ 0 } }=\dfrac { { { V_{ 0 } } } }{ Z } =\dfrac { { 20 } }{ { 10 } } =2A \\ Hence\, \, { i_{ rms } }=\dfrac { 2 }{ { \sqrt { 2 } } } =1.4\, A \\ and\, \, { V_{ rms } }=4\times 1.41=5.64\, V \end{array}$$
Hence,
option $$(B)$$ is correct answer.
Question 3
1 / -0

A direct current of 10 A is superimposed on an alternating current $$l=40\cos\omega t\left( A \right) $$ flowing through a wire. The effective value of the resulting current will be

A
$$10\sqrt { 2 } A$$

B
$$20\sqrt { 2 } A$$

C
$$20\sqrt { 3 } A$$

D
30 A

Solution
Question 4
1 / -0

A student connects a long air cored coil of manganin wire to a $$100VD.C.$$ supply and records a current of $$25amp$$. When the same coil is connected across $$100V.50z a.c.$$ the current reduces to $$20A$$, the reactance of the coil is:-

A
$$4\Omega$$

B
$$3\Omega$$

C
$$5\Omega$$

D
$$None$$

Solution
Question 5
1 / -0

If resonant frequency of a R-L-C circuit is $$\Delta \omega $$, then which of the following quantity is regarded as a measure of the sharpness of resonance?

A
$$\frac { \omega _0 }{ \Delta\omega } $$

B
$$\frac { \omega _0 }{ 2\Delta\omega } $$

C
$$\frac { 2\omega _0 }{ \Delta\omega } $$

D
$$\frac { \omega _0 }{ 2\omega } $$

Solution
Question 6
1 / -0

An alternating current is given by
$$i={i}_{1}\cos{\omega t}+{i}_{2}\sin{\omega t}$$. The rms current is given by:

A
$$\cfrac{{i}_{1}+{i}_{2}}{\sqrt{2}}$$

B
$$\cfrac { \left| { i }_{ 1 }+{ i }_{ 2 } \right| }{ \sqrt { 2 } } $$

C
$$\sqrt { \cfrac { { i }_{ 1 }^{ 2 }+{ i }_{ 2 }^{ 2 } }{ 2 } } $$

D
$$\sqrt { \cfrac { { i }_{ 1 }^{ }+{ i }_{ 2 }^{ } }{ 2 } } $$

Solution
Question 7
1 / -0

The most appropriate I-H curve for a paramagnetic substance is:

A
$$OA$$

B
$$OB$$

C
$$OC$$

D
$$OD$$

Solution
Question 8
1 / -0

The tuned collector oscillator circuit used in the local oscillator of a radius receiver makes use of a tuned circuit with $$L=60\mu H$$ and $$C=400pF$$.
Calculate the frequency of oscillations

A
$$1.03KHz$$

B
$$1.03Hz$$

C
$$1.03GHz$$

D
$$1.03MHz$$

Solution
Question 9
1 / -0

In the given circuit $$R$$ is a resistor. $$L$$ is an inductor and $$B _ { 1 }$$ and $$B _ { 2 }$$ are two bulbs and initially the switch $$S$$ was closed. If the switch $$S$$ is turned off. Then

A
Both $$B _ { 1 }$$ and $$B _ { 2 }$$ die out promptly

B
Both $$B _ { 1 }$$ and $$B _ { 2 }$$ die out with some delay

C
$$B _ { 1 }$$ die out promptly but $$B _ { 2 }$$ with some delay

D
$$B _ { 2 }$$ die out promptly but $$B _ { 1 }$$ with some delay

Solution
Question 10
1 / -0

Alternating current is given by i = (3 sin $$\omega$$ t + 4 cos $$\omega$$ t)A the rms current will be

A
$$\frac{7}{\sqrt 2}$$ A

B
$$\frac{1}{\sqrt 2}$$ A

C
$$\frac{5}{\sqrt 2}$$ A

D
$$\frac{3}{\sqrt 2}$$ A

Solution