MCQ

MCQ 511 Mark

What type of modulation is employed in India for radio transmission

✓
Amplitude modulation
B
Frequency modulation
C
Pulse modulation
D
None of these

Answer

Correct option: A.

Amplitude modulation

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MCQ 521 Mark

The frequency of a FM transmitter without signal input is called

A
Lower side band frequency
B
Upper side band frequency
✓
Resting frequency
D
None of these

Answer

Correct option: C.

Resting frequency

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MCQ 531 Mark

An AM wave has $1800$ watt of total power content, For $100 \%$ modulation the carrier should have power content equal to

A
$1000 \mathrm{watt}$
✓
$1200 \mathrm{watt}$
C
$1500 \mathrm{watt}$
D
$1600 \mathrm{watt}$

Answer

Correct option: B.

$1200 \mathrm{watt}$

$ P_t=P_c\left(1+\frac{m_a^2}{2}\right) ; \text { Here } m=1$
$ \Rightarrow 1800=P_c\left(1+\frac{(1)^2}{2}\right) \Rightarrow P_c=1200 \mathrm{~W}$

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MCQ 541 Mark

If a number of sine waves with modulation indices $n, n, n \ldots \ldots$ modulate a carrier wave, then total modulation index $(n)$ of the wave is

A
$n+n_1 \ldots+2(n+n \ldots .$.
B
$\sqrt{n_1-n_2+n_3 \ldots \ldots \ldots}$
✓
$\sqrt{n_1^2+n_2^2+n_3^2 \cdots \cdots \cdots}$
D
None of these

Answer

Correct option: C.

$\sqrt{n_1^2+n_2^2+n_3^2 \cdots \cdots \cdots}$

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MCQ 551 Mark

Which of the following is the disadvantage of FM over AM

✓
Larger band width requirement
B
Larger noise
C
Higher modulation power
D
Low efficiency

Answer

Correct option: A.

Larger band width requirement

Frequency modulation requires much wider channel ($7$ to $15$ times) as compared to AM.

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MCQ 561 Mark

If $f$ and $f$ represent the carrier wave frequencies for amplitude and frequency modulations respectively, then

A
(a) $f_a>f_f$
✓
(b) $f_a
C
(c) $f_a \approx f_f$
D
(d) $f_a \geq f_f$

Answer

Correct option: B.

(b) $f_a

(b)

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MCQ 571 Mark

Basically, the product modulator is

A
An amplifier
✓
A mixer
C
A frequency separator
D
A phase separator

Answer

Correct option: B.

A mixer

It mix weak signals with carrier signals.

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MCQ 581 Mark

What is the modulation index of an over modulated wave

A
$ 1 $
B
Zero
C
$<1$
✓
$>1$

Answer

Correct option: D.

$>1$

When $m>1$ then carrier is said to be over modulated.

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MCQ 591 Mark

Sinusoidal carrier voltage of frequency $1.5 \mathrm{MHz}$ and amplitude $50 \mathrm{~V}$ is amplitude modulated by sinusoidal voltage of frequency $10 \mathrm{kHz}$ producing $50 \%$ modulation. The lower and upper side-band frequencies in $\mathrm{kHz}$ are

✓
$1490,1510$
B
$1510,1490$
C
$\frac{1}{1490}, \frac{1}{1510}$
D
$\frac{1}{1510}, \frac{1}{1490}$

Answer

Correct option: A.

$1490,1510$

Here, $f_c=1.5 \mathrm{MHz}=1500 \mathrm{kHz}, f_m=10 \mathrm{kHz}$
$\therefore$ Low side band frequency$=f_c-f_m=1500 \mathrm{kHz}-10 \mathrm{kHz}=1490 \mathrm{kHz}$
Upper side band frequency$=f_c+f_m=1500 \mathrm{kHz}+10 \mathrm{kHz}=1510 \mathrm{kHz}$

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MCQ 601 Mark

The maximum peak to peak voltage of an AM wire is $24 \mathrm{mV}$ and the minimum peak to peak voltage is $8 \mathrm{mV}$. The modulation factor is

A
$10 \%$
B
$20 \%$
C
$25 \%$
✓
$50 \%$

Answer

Correct option: D.

$50 \%$

Here, $V_{\max }=\frac{24}{2}=12 \mathrm{mV}$ and $V_{\min }=\frac{8}{2}=2 \mathrm{mV}$
Now, $m=\frac{V_{\max }-V_{\min }}{V_{\max }+V_{\min }}=\frac{12-4}{12+4}=\frac{8}{16}=\frac{1}{2}=0.5=50 \%$

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MCQ 611 Mark

The electromagnetic waves of frequency $2 \mathrm{MHz}$ to $30 \mathrm{MHz}$ are

A
In ground wave propagation
✓
In sky wave propagation
C
In microwave propagation
D
In satellite communication

Answer

Correct option: B.

In sky wave propagation

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MCQ 621 Mark

An antenna behaves as resonant circuit only when its length is

A
$\frac{\lambda}{2}$
B
$\frac{\lambda}{4}$
C
$\lambda$
✓
$\frac{\lambda}{2}$ or integral multiple of $\frac{\lambda}{2}$

Answer

Correct option: D.

$\frac{\lambda}{2}$ or integral multiple of $\frac{\lambda}{2}$

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MCQ 631 Mark

The radio waves of frequency $300 \mathrm{MHz}$ to $3000 \mathrm{MHz}$ belong to

A
High frequency band
B
Very high frequency band
✓
Ultra high frequency band
D
Super high frequency band

Answer

Correct option: C.

Ultra high frequency band

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MCQ 641 Mark

For television broadcasting, the frequency employed is normally

✓
$30-300 \mathrm{MHz}$
B
$30-300 \mathrm{GHz}$
C
$30-300 \mathrm{KHz}$
D
$30-300 \mathrm{~Hz}$

Answer

Correct option: A.

$30-300 \mathrm{MHz}$

VHF (Very High Frequency) band having frequency range 30 $M H z$ to $300 \mathrm{MHz}$ is typically used for TV and radar transmission.

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MCQ 651 Mark

A laser beam of pulse power $10-$ watt is focussed on an object are $10^{-}$ $\mathrm{cm}$. The energy flux in watt/ $\mathrm{cm}$ at the point of focus is

A
$10^{-1} cm^2$
B
$ 10^1 cm^2$
✓
$10^2 \ cm^2$
D
$10^3 cm^2$

Answer

Correct option: C.

$10^2 \ cm^2$

$10^2 cm^2$

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MCQ 661 Mark

$\mathrm{AM}$ is used for broadcasting because

A
It is more noise immune than other modulation systems
B
It requires less transmitting power compared with other systems
✓
Its use avoids receiver complexity
D
No other modulation system can provide the necessary bandwidth faithful transmission

Answer

Correct option: C.

Its use avoids receiver complexity

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JEE physics MCQ