COMMUNICATION SYSTEMS MCQs for NEET UG PHYSICS — Easy

1 Easy

Understanding +4 | -1

In the communication systems, AM is used for broadcasting because

View answer and explanation

Correct option: A

Its use avoids receiver complexity

Option A (Its use avoids receiver complexity) is the reason AM is used for broadcasting, as it simplifies the design and cost of receivers.

Solution approach

Correct Answer + Core Reason: AM is used for broadcasting because its use avoids receiver complexity.

Step-by-Step Solution:

Step 1: Consider the requirements for broadcasting: simple and inexpensive receivers.

Step 2: AM receivers are simpler and cheaper to manufacture than FM or other modulation schemes.

Step 3: Simplicity in receiver design is crucial for widespread adoption in broadcasting.

Why other options are wrong:
- Option B: AM is actually more susceptible to noise than FM.
- Option C: AM requires more transmitting power than some other modulation techniques.
- Option D: Other modulation systems can provide the necessary bandwidth, but at the cost of increased receiver complexity.

Key Concepts:
- Amplitude Modulation (AM)
- Receiver Complexity
- Broadcasting Requirements

Memory Aids:
- AM = Affordable Modulation (simple receivers)

Quick Tips:
- Remember that AM's main advantage is the simplicity of its receivers.

2 Easy

2 of 17Question permalink

Application +4 | -1

The maximum and minimum voltage of an amplitude modulated signal are

60 \mathrm{~V}

and

20 \mathrm{~V}

respectively. The percentage modulation index will be:

View answer and explanation

Correct option: B

50 \%

Option B (50%) is correct because the percentage modulation index is calculated as ((Vmax - Vmin) / (Vmax + Vmin)) * 100.

Solution approach

Correct Answer + Core Reason: 50 %. The percentage modulation index is calculated using the formula based on maximum and minimum voltages.

Step-by-Step Solution:

Step 1: Identify the given information: Maximum voltage ( $V_{max}$ ) = 60 V, Minimum voltage ( $V_{min}$ ) = 20 V.

Step 2: Recall the formula for modulation index ( $m$ ) in AM modulation: $m = \frac{{V_{max} - V_{min}}}{{V_{max} + V_{min}}}$

Step 3: Calculate the modulation index: $m = \frac{{60 - 20}}{{60 + 20}} = \frac{40}{80} = 0.5$

Step 4: Calculate the percentage modulation index: Percentage modulation = $m \times 100 = 0.5 \times 100 = 50 \%$

Step 5: Final Answer: The percentage modulation index is 50%.

Why other options are wrong:
- Option A (0.5 %): This is incorrect because it represents the modulation index without converting it to a percentage.
- Option C (2 %): This is incorrect as it doesn't result from the correct application of the percentage modulation index formula.
- Option D (30 %): This is incorrect as it doesn't result from the correct application of the percentage modulation index formula.

Key Concepts:
- Amplitude Modulation (AM)
- Modulation Index
- Percentage Modulation

Memory Aids:
- Remember to multiply the modulation index by 100 to get the percentage.

Quick Tips:
- Always remember to convert the modulation index to percentage when asked for percentage modulation.

3 Easy

3 of 17Question permalink

Remembering +4 | -1

Depth of modulation

\left( {{m_a}} \right)

in terms of

{{\text{E}}_{{\text{max}}}}\,{\text{and}}\,{{\text{E}}_{{\text{min}}}}

is

View answer and explanation

Correct option: C

{{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}

Option C,

{{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}

, is the correct formula for calculating the depth of modulation (

m_a

) in terms of the maximum and minimum amplitudes of the modulated wave.

Solution approach

Correct Answer + Core Reason: ${{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}$ . This is the standard formula for depth of modulation.

Step-by-Step Solution:

Step 1: Define depth of modulation ( $m_a$ ). Depth of modulation is a measure of the extent to which the amplitude of the carrier wave is varied by the message signal.

Step 2: Recall the formula for depth of modulation in terms of $E_{max}$ and $E_{min}$ :
$m_a = \frac{{E_{max} - E_{min}}}{{E_{max} + E_{min}}}$

Step 3: Compare the given options with the correct formula.

Why other options are wrong:
- Option A: ${{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ + }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{min}}}}$ is incorrect. The numerator should be the difference, not the sum.
- Option B: ${{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}}$ is incorrect. The denominator should be the sum, not just the maximum.
- Option D: ${{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ + }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}$ is incorrect. The numerator should be the difference, not the sum.

Key Concepts:
- Amplitude Modulation (AM)
- Depth of Modulation

Memory Aids:
- Remember the formula: $m_a = \frac{{E_{max} - E_{min}}}{{E_{max} + E_{min}}}$

Quick Tips:
- Understand the relationship between $E_{max}$ , $E_{min}$ , and the amplitude of the message signal and carrier wave.

4 Easy

4 of 17Question permalink

Remembering +4 | -1

The process of superimposing signal frequency (i.e., audio wave) on the carrier wave is known as

View answer and explanation

Correct option: C

Modulation

Option C (Modulation) is correct because modulation is the process of superimposing a signal onto a carrier wave.

Solution approach

Correct Answer + Core Reason: Modulation is the process of superimposing a signal onto a carrier wave.

Step-by-Step Solution:

Step 1: Define the terms.

Step 2: Modulation is the process of varying one or more properties of a carrier wave with a modulating signal.

Step 3: Transmission is the process of sending a signal over a medium.

Step 4: Reception is the process of receiving a signal.

Step 5: Detection is the process of extracting the original signal from the modulated wave.

Step 6: Therefore, the correct answer is modulation.

Why other options are wrong:
- Option A: Transmission is the process of sending the modulated wave, not the superimposition itself.
- Option B: Reception is the process of receiving the modulated wave, not the superimposition itself.
- Option D: Detection is the process of extracting the original signal, not the superimposition itself.

Key Concepts:
- Modulation
- Transmission
- Reception
- Detection

Memory Aids:
- Modulation: Think of \"modifying\" the carrier wave.

Quick Tips:
- Understand the definitions of each term in communication systems.

5 Easy

5 of 17Question permalink

Application +4 | -1

An audio signal of amplitude one half the carrier amplitude is used in amplitude modulation. Calculate the modulation index?

View answer and explanation

Correct option: A

0.5

Option A (0.5) is correct because the modulation index is the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

Solution approach

Correct Answer + Core Reason: 0.5. The modulation index is the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

Step-by-Step Solution:

Step 1: Define the variables: Let $A_m$ be the amplitude of the modulating signal and $A_c$ be the amplitude of the carrier signal.

Step 2: Given that the amplitude of the audio signal is one half the carrier amplitude, we have $A_m = \frac{1}{2} A_c$ .

Step 3: The modulation index ( $m$ ) is defined as: $m = \frac{{A_m}}{{A_c}}$

Step 4: Substitute the given relationship: $m = \frac{{\frac{1}{2} A_c}}{{A_c}}$

Step 5: Simplify: $m = \frac{1}{2} = 0.5$

Step 6: Final Answer: The modulation index is 0.5.

Why other options are wrong:
- Option B (0): This is incorrect because the modulating signal has a non-zero amplitude.
- Option C (0): This is incorrect because the modulating signal has a non-zero amplitude.
- Option D (0): This is incorrect because the modulating signal has a non-zero amplitude.

Key Concepts:
- Amplitude Modulation (AM)
- Modulation Index

Memory Aids:
- Remember the formula for modulation index: $m = \frac{{A_m}}{{A_c}}$

Quick Tips:
- Always identify the amplitudes of the modulating and carrier signals correctly.

6 Easy

6 of 17Question permalink

Understanding +4 | -1

When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity

ie

, dielectric constant dielectric constant of the ionised layer

View answer and explanation

Correct option: C

Appears to decrease

The correct answer is C (Appears to decrease) because the refractive index of the ionosphere is related to the electron density, and as electromagnetic waves enter, the effective dielectric constant decreases.

Solution approach

Correct Answer + Core Reason: Appears to decrease. The relative permittivity of the ionized layer decreases when electromagnetic waves enter.

Step-by-Step Solution:

Step 1: Recall the relationship between relative permittivity and refractive index in the ionosphere.

Step 2: The relative permittivity (dielectric constant) of the ionosphere is related to the electron density. As the electromagnetic waves interact with the ionized layer, the effective dielectric constant decreases.

Step 3: Therefore, the relative permittivity appears to decrease.

Why other options are wrong:
- Option A: Does not change - The permittivity changes due to the interaction of the electromagnetic waves with the ionized particles.
- Option B: Appears to increase - The permittivity decreases, not increases.
- Option D: Sometimes appears to increase and sometimes to decrease - The permittivity consistently decreases as the waves enter the ionized layer.

Key Concepts:
- Ionosphere
- Relative Permittivity (Dielectric Constant)
- Electromagnetic Waves

Memory Aids:
- Remember that the ionosphere is ionized, and the interaction with EM waves reduces the effective permittivity.

Quick Tips:
- Understand the basic properties of the ionosphere and its interaction with electromagnetic waves.

7 Easy

7 of 17Question permalink

Understanding +4 | -1

In frequency modulated wave

View answer and explanation

Correct option: A

Frequency varies with time

The correct answer is A (Frequency varies with time) because, by definition, in frequency modulation, the frequency of the carrier wave is varied according to the message signal.

Solution approach

Correct Answer + Core Reason: Frequency varies with time. In frequency modulation (FM), the frequency of the carrier signal changes with the message signal.

Step-by-Step Solution:

Step 1: Understand the concept of Frequency Modulation (FM).

Step 2: In FM, the instantaneous frequency of the carrier wave is varied in proportion to the message signal's amplitude.

Step 3: Therefore, the frequency varies with time.

Why other options are wrong:
- Option B: Amplitude varies with time - This is the principle of Amplitude Modulation (AM), not FM.
- Option C: Both frequency and amplitude vary with time - Only frequency varies in FM.
- Option D: Both frequency and amplitude are constant - This is true for an unmodulated carrier wave.

Key Concepts:
- Frequency Modulation (FM)
- Amplitude Modulation (AM)
- Carrier Wave
- Message Signal

Memory Aids:
- FM: Frequency changes with the message.

Quick Tips:
- Remember the basic definitions of AM and FM.

8 Easy

8 of 17Question permalink

Application +4 | -1

In AM modulation, a signal is modulated on a carrier wave such that maximum and minimum amplitudes are found to be

6 \mathrm{~V}

and

2 \mathrm{~V}

respectively. The modulation index is

View answer and explanation

Correct option: D

0.5

Option D (0.5) is correct because the modulation index is calculated as (Amax - Amin) / (Amax + Amin).

Solution approach

Correct Answer + Core Reason: 0.5. The modulation index is calculated using the formula based on maximum and minimum amplitudes.

Step-by-Step Solution:

Step 1: Identify the given information: Maximum amplitude ( $A_{max}$ ) = 6 V, Minimum amplitude ( $A_{min}$ ) = 2 V.

Step 2: Recall the formula for modulation index ( $m$ ) in AM modulation: $m = \frac{{A_{max} - A_{min}}}{{A_{max} + A_{min}}}$

Step 3: Substitute the given values into the formula: $m = \frac{{6 - 2}}{{6 + 2}}$

Step 4: Calculate the modulation index: $m = \frac{4}{8} = 0.5$

Step 5: Final Answer: The modulation index is 0.5.

Why other options are wrong:
- Option A (1): This is incorrect because it would imply that the minimum amplitude is zero, which is not the case here.
- Option B (0.8): This is incorrect as it doesn't result from the correct application of the modulation index formula.
- Option C (0.6): This is incorrect as it doesn't result from the correct application of the modulation index formula.

Key Concepts:
- Amplitude Modulation (AM)
- Modulation Index

Memory Aids:
- Remember the formula: $m = \frac{{A_{max} - A_{min}}}{{A_{max} + A_{min}}}$

Quick Tips:
- Always identify the maximum and minimum amplitudes correctly before applying the formula.

9 Easy

9 of 17Question permalink

Application +4 | -1

Find the modulation index of an AM wave having 8

\mathrm{V}

variation where maximum amplitude of the AM wave is

9 \mathrm{~V}

.

View answer and explanation

Correct option: A

0.8

Option A (0.8) is correct because the modulation index is calculated as variation/ (2 * A_carrier), where A_carrier is A_max - variation/2.

Solution approach

Correct Answer + Core Reason: 0.8. The modulation index is calculated using the formula based on the variation and maximum amplitude.

Step-by-Step Solution:

Step 1: Identify the given information: Variation = 8 V, Maximum amplitude ( $A_{max}$ ) = 9 V.

Step 2: Determine the carrier amplitude ( $A_c$ ). Since the variation is 8V, the minimum amplitude is $9 - 8 = 1$ V. The carrier amplitude is the average of the max and min amplitudes: $A_c = (9 + 1)/2 = 5$ V.

Step 3: Calculate the modulation index ( $m$ ) using the formula: $m = \frac{{\text{{Variation}}}}{{2A_c}} = \frac{8}{2*5} = \frac{8}{10} = 0.8$

Step 4: Final Answer: The modulation index is 0.8.

Why other options are wrong:
- Option B (0.5): This is incorrect as it doesn't result from the correct application of the modulation index formula with the given variation and maximum amplitude.
- Option C (0.2): This is incorrect as it doesn't result from the correct application of the modulation index formula with the given variation and maximum amplitude.
- Option D (0.1): This is incorrect as it doesn't result from the correct application of the modulation index formula with the given variation and maximum amplitude.

Key Concepts:
- Amplitude Modulation (AM)
- Modulation Index

Memory Aids:
- Remember the relationship between variation, maximum amplitude, and modulation index.

Quick Tips:
- Ensure you correctly determine the carrier amplitude from the given variation and maximum amplitude.

10 Easy

10 of 17Question permalink

Remembering +4 | -1

In earth's atmosphere, for E-layer, the virtual height and critical frequency are

View answer and explanation

Correct option: D

110 km and 4 MHz

Option D, 110 km and 4 MHz, is the closest to the typical values for the E-layer virtual height and critical frequency in Earth's atmosphere.

Solution approach

Correct Answer + Core Reason: 110 km and 4 MHz. These are the approximate values for the E-layer's virtual height and critical frequency.

Step-by-Step Solution:

Step 1: Recall the different layers of the ionosphere: D, E, F1, and F2 layers.

Step 2: Remember the approximate altitudes and critical frequencies for each layer:
- D layer: 60-90 km, absorbs medium and high frequencies during the day.
- E layer: 90-150 km, reflects high frequencies during the day, disappears at night. Virtual height is around 110 km and critical frequency is around 4 MHz.
- F1 layer: 150-250 km, exists during the day, merges with F2 layer at night.
- F2 layer: 250-400 km, most important layer for long-distance radio communication.

Step 3: Identify the option that matches the E-layer characteristics.

Why other options are wrong:
- Option A: 80 km is too low for the E-layer, and 3 MHz is a lower critical frequency than typical.
- Option B: 90 km is slightly low for the E-layer, and 3.5 MHz is a lower critical frequency than typical.
- Option C: 120 km is within the E-layer range, but 4.5 MHz is a slightly higher critical frequency than typical.

Key Concepts:
- Ionosphere layers (D, E, F1, F2)
- Virtual height
- Critical frequency

Memory Aids:
- Remember the order of the layers: D-E-F (lowest to highest).

Quick Tips:
- Memorize the approximate altitudes and critical frequencies of the ionospheric layers.

11 Easy

11 of 17Question permalink

Remembering +4 | -1

The sky wave propagation is suitable for radio-waves of frequency

View answer and explanation

Correct option: C

From 2 MHz to 30 MHz

Option C, From 2 MHz to 30 MHz, is correct because sky wave propagation, which relies on ionospheric reflection, is most effective within this frequency range.

Solution approach

Correct Answer + Core Reason: From 2 MHz to 30 MHz. Sky wave propagation is suitable for radio waves in this frequency range.

Step-by-Step Solution:

Step 1: Understand sky wave propagation. Sky wave propagation (also known as ionospheric propagation) involves the transmission of radio waves that are reflected or refracted by the ionosphere back to Earth.

Step 2: Recall the frequency ranges suitable for different propagation methods:
- Ground wave propagation: Low frequencies (up to 2 MHz), follows the curvature of the Earth.
- Sky wave propagation: Medium and high frequencies (2 MHz to 30 MHz), reflected by the ionosphere.
- Space wave propagation: Very high frequencies (above 30 MHz), travels in a straight line.

Step 3: Identify the option that corresponds to sky wave propagation.

Why other options are wrong:
- Option A: Upto 2 MHz is suitable for ground wave propagation.
- Option B: From 2 MHz to 20 MHz is a subset of the correct range, but not the complete range.
- Option D: From 2 MHz to 50 MHz includes frequencies that are more suitable for space wave propagation.

Key Concepts:
- Sky wave propagation
- Ionosphere
- Ground wave propagation
- Space wave propagation

Memory Aids:
- Sky wave: Think of waves bouncing off the sky (ionosphere).

Quick Tips:
- Remember the frequency ranges for different radio wave propagation methods.

12 Easy

12 of 17Question permalink

Application +4 | -1

The audio signal used to modulate

60\sin \left( {2\pi \times {{10}^6}\;t} \right)

is 

15\,\,\sin \,\,300\pi t.

The depth of modulation is

View answer and explanation

Correct option: C

0.25

Option C (0.25) is correct because the depth of modulation is calculated as the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

Solution approach

Correct Answer + Core Reason: 0.25. Depth of modulation is the ratio of modulating signal amplitude to carrier signal amplitude.

Step-by-Step Solution:

Step 1: Identify the carrier signal: $60\sin(2\pi \times 10^6 t)$ . Its amplitude is $A_c = 60$ .

Step 2: Identify the modulating signal: $15\sin(300\pi t)$ . Its amplitude is $A_m = 15$ .

Step 3: Calculate the depth of modulation ( $\mu$ ): $\mu = \frac{A_m}{A_c}$

Step 4: Substitute the values: $\mu = \frac{15}{60}$

Step 5: Simplify: $\mu = 0.25$

Why other options are wrong:
- Option A: 0.5 is incorrect. It might be obtained by incorrectly dividing 30 by 60.
- Option B: 0.4 is incorrect. There is no direct calculation that leads to this value.
- Option D: 0.15 is incorrect. It might be obtained by incorrectly dividing 9 by 60 (15% of 60 is 9, not related to depth of modulation).

Key Concepts:
- Amplitude Modulation (AM)
- Depth of Modulation
- Carrier Signal
- Modulating Signal

Memory Aids:
- Modulation = Message / Carrier: Remember that the depth of modulation is the ratio of the message signal amplitude to the carrier signal amplitude.

Quick Tips:
- Always identify the carrier and modulating signals correctly before calculating the depth of modulation.

13 Easy

13 of 17Question permalink

Remembering +4 | -1

Major parts of a communication system are

View answer and explanation

Correct option: D

Transmitter, receiver and communication channel

Option D, Transmitter, receiver and communication channel, is correct because these are the three essential components for any communication system to function.

Solution approach

Correct Answer + Core Reason: Transmitter, receiver and communication channel. These are the three essential components of a communication system.

Step-by-Step Solution:

Step 1: Define a communication system. A communication system is a system that allows the transfer of information from one point to another.

Step 2: Identify the essential components:
- Transmitter: Converts the message signal into a suitable form for transmission.
- Communication Channel: The medium through which the signal travels from the transmitter to the receiver.
- Receiver: Extracts the message signal from the received signal.

Step 3: Consider the other options and why they are incomplete.

Why other options are wrong:
- Option A: Transmitter and receiver are necessary, but the communication channel is also essential.
- Option B: Receiver and communication channel are necessary, but the transmitter is also essential.
- Option C: Transmitter and communication channel are necessary, but the receiver is also essential.

Key Concepts:
- Communication System
- Transmitter
- Receiver
- Communication Channel

Memory Aids:
- Think of a phone call: You (transmitter), the phone lines (channel), and the person you're calling (receiver).

Quick Tips:
- Remember the basic block diagram of a communication system.

14 Easy

14 of 17Question permalink

Understanding +4 | -1

A laser beam is used for carrying out surgery because it

View answer and explanation

Correct option: D

Can be sharply focused

The correct answer is D (Can be sharply focused) because the ability to focus a laser beam to a small spot allows for precise cutting or ablation of tissue during surgery.

Solution approach

Correct Answer + Core Reason: Can be sharply focused. This allows for precise cutting and ablation of tissue.

Step-by-Step Solution:

Step 1: Consider the properties of laser beams.

Step 2: Laser beams can be highly monochromatic, coherent, and directional, but the key property for surgery is their ability to be focused to a very small spot.

Step 3: This allows for precise cutting or ablation of tissue.

Why other options are wrong:
- Option A: Is highly monochromatic - While lasers are monochromatic, this isn't the primary reason for their use in surgery. Monochromaticity is related to the precision of the laser's wavelength, but not directly to its cutting ability.
- Option B: Is highly coherent - Coherence is important for maintaining the beam's focus over a distance, but the focusing itself is the key factor.
- Option C: Is highly directional - Directionality helps to deliver the beam to the target area, but the focusing is what enables the surgical effect.

Key Concepts:
- Laser Properties (Monochromaticity, Coherence, Directionality, Focusability)
- Laser Surgery

Memory Aids:
- Think of a magnifying glass focusing sunlight to a point to burn something. Lasers do the same, but with much higher precision.

Quick Tips:
- Consider the specific application when evaluating the importance of different laser properties.

15 Easy

15 of 17Question permalink

Remembering +4 | -1

The mobile telephones operate typically in the range of

View answer and explanation

Correct option: D

800-950 MHz

Option D, 800-950 MHz, is the typical frequency range in which mobile telephones operate.

Solution approach

Correct Answer + Core Reason: 800-950 MHz. This is the typical frequency range for mobile phone operation.

Step-by-Step Solution:

Step 1: Recall the frequency bands used for mobile communication.

Step 2: Common frequency bands for mobile phones include:
- 800-950 MHz (e.g., GSM, CDMA)
- 1700-2100 MHz (e.g., 3G, UMTS)
- 2500-2700 MHz (e.g., 4G, LTE)

Step 3: Identify the option that falls within the typical mobile phone frequency range.

Why other options are wrong:
- Option A: 1-100 MHz is too low for typical mobile phone operation. This range is used for FM radio and some VHF communication.
- Option B: 100-200 MHz is also too low for typical mobile phone operation. This range is used for VHF television broadcasting.
- Option C: 1000-2000 MHz is a valid range for some mobile phone technologies (like 3G), but 800-950 MHz is more common and fundamental.

Key Concepts:
- Mobile communication frequencies
- GSM, CDMA, UMTS, LTE

Memory Aids:
- Remember the approximate frequency ranges for different mobile technologies.

Quick Tips:
- Be aware of the common frequency bands used for mobile communication.

16 Easy

16 of 17Question permalink

Application +4 | -1

At a particular station, the TV transmission tower has a height of

100 \mathrm{~m}

. To triple its coverage range, height of the tower should be increased to

View answer and explanation

Correct option: D

900 \mathrm{~m}

Option D (900 m) is correct because the coverage range is proportional to the square root of the height of the tower.

Solution approach

Correct Answer + Core Reason: 900 m. The coverage range is proportional to the square root of the height of the tower.

Step-by-Step Solution:

Step 1: Understand the relationship between coverage range (d) and height of the tower (h): $d \propto \sqrt{h}$

Step 2: Let $d_1$ be the initial coverage range and $h_1$ be the initial height, and $d_2$ be the final coverage range and $h_2$ be the final height. We have: $\frac{{d_2}}{{d_1}} = \sqrt{\frac{{h_2}}{{h_1}}}$

Step 3: Given that the coverage range is tripled, $d_2 = 3d_1$ . Also, $h_1 = 100 \text{{ m}}$ . We need to find $h_2$ .

Step 4: Substitute the given values: $\frac{{3d_1}}{{d_1}} = \sqrt{\frac{{h_2}}{{100}}}$

Step 5: Simplify: $3 = \sqrt{\frac{{h_2}}{{100}}}$

Step 6: Square both sides: $9 = \frac{{h_2}}{{100}}$

Step 7: Solve for $h_2$ : $h_2 = 9 \times 100 = 900 \text{{ m}}$

Step 8: Final Answer: The height of the tower should be increased to 900 m.

Why other options are wrong:
- Option A (200 m): This is incorrect because it would only double the height, not triple the coverage range.
- Option B (300 m): This is incorrect because it would not triple the coverage range, as the range is proportional to the square root of the height.
- Option C (600 m): This is incorrect because it would not triple the coverage range, as the range is proportional to the square root of the height.

Key Concepts:
- Relationship between coverage range and height of the antenna

Memory Aids:
- Remember that the coverage range is proportional to the square root of the height.

Quick Tips:
- When dealing with coverage range and height problems, remember the square root relationship.

17 Easy

17 of 17Question permalink

Understanding +4 | -1

Which one of the following is a full duplex transmission system?

View answer and explanation

Correct option: C

Telephone

Option C (Telephone) is a full-duplex system because it allows simultaneous two-way communication between two parties.

Solution approach

Correct Answer + Core Reason: Telephone is a full-duplex system, allowing simultaneous two-way communication.

Step-by-Step Solution:

Step 1: Define full-duplex transmission: simultaneous two-way communication.

Step 2: TV and Radio are simplex (one-way) communication systems.

Step 3: Walkie-talkies are half-duplex (two-way, but not simultaneous).

Step 4: Telephones allow both parties to speak and listen at the same time.

Why other options are wrong:
- Option A: TV is a simplex communication system (one-way).
- Option B: Radio is a simplex communication system (one-way).
- Option D: Walkie-talky is a half-duplex system, requiring users to take turns speaking.

Key Concepts:
- Simplex, Half-Duplex, and Full-Duplex Communication

Memory Aids:
- Telephone = Two-way, Together (Full-Duplex)

Quick Tips:
- Remember the definitions of simplex, half-duplex, and full-duplex to easily identify the correct system.

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