What is a transducer? Name two (2) types of electro-acoustic transducers. Name two (2) types of electromagnetic transducers. Explain how a carbon microphone works.

The speed of the wave is $\boxed{\text{350 m/s}}$.

Q3a) State the differences between Amplitude Modulation (AM) and Frequency Modulation (FM).

• In Amplitude Modulation (AM), the amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal, while its frequency and phase remain constant.
• In Frequency Modulation (FM), the frequency of the carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal, while its amplitude remains constant.

Q3b) A 10 MHz sinusoidal carrier wave of amplitude 10 mV is modulated by a 5 kHz sinusoidal audio signal of amplitude 6 mV. Find the frequency components of the resultant modulated wave.

The resultant AM wave consists of the carrier frequency ($f_c$), the upper sideband frequency ($f_c + f_m$), and the lower sideband frequency ($f_c - f_m$).

Upper Sideband (USB) frequency:

Lower Sideband (LSB) frequency:

The frequency components are $\boxed{\text{10 MHz, 10.005 MHz, and 9.995 MHz}}$.

Q4a) Define the following terms:

• i. Pitch: The perceptual property of sounds that allows their ordering on a frequency-related scale, primarily determined by the fundamental frequency of the sound wave.
• ii. Sound echoes: A reflection of sound that arrives at the listener with a noticeable delay after the direct sound, caused by the sound wave bouncing off a distant surface.

Q4b) i. State four (4) characteristics of electromagnetic waves.

1. They are transverse waves.
2. They can travel through a vacuum.
3. They travel at the speed of light in a vacuum ($c \approx 3 \times 10^8 \text{ m/s}$).
4. They consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation.

Q4b) ii. Give four (4) characteristics of sound waves.

1. They are longitudinal waves (in fluids).
2. They require a medium for propagation and cannot travel through a vacuum.
3. They travel much slower than electromagnetic waves.
4. They are mechanical waves, caused by vibrations of particles in a medium.

Q5) Two observers P and Q, 150,000 mm apart, are each 300,000 mm from a long vertical pole. A sound from observer P is echoed back to observer Q in a time of 2540 ms. Find the velocity of the sound issued from observer P.

Distance P to Pole = $300,000 \text{ mm} = 300 \text{ m}$
Distance Q to Pole = $300,000 \text{ mm} = 300 \text{ m}$
Time taken ($t$) = $2540 \text{ ms} = 2.540 \text{ s}$

The sound travels from observer P to the pole, then reflects off the pole and travels to observer Q.
Total distance ($D$) = (Distance P to Pole) + (Distance Pole to Q)

Velocity ($v$) = Total Distance ($D$) / Time ($t$)

The velocity of the sound is $\boxed{\text{236.22 m/s}}$.

Q6a) With reference to telecommunication, explain the term filters.
In telecommunication, filters are electronic circuits or devices designed to selectively pass signals within a specific range of frequencies while attenuating or blocking signals outside that range. They are crucial for separating desired information from noise and interference.

Q6b) i. Name four (4) types of filters.

1. Low-pass filter
2. High-pass filter
3. Band-pass filter
4. Band-stop filter

Q6b) ii. State the function of each.

1. Low-pass filter: Allows frequencies below a specified cutoff frequency to pass and attenuates frequencies above it.
2. High-pass filter: Allows frequencies above a specified cutoff frequency to pass and attenuates frequencies below it.
3. Band-pass filter: Allows frequencies within a specific range (band) to pass and attenuates frequencies outside this range.
4. Band-stop filter: Attenuates frequencies within a specific range (band) and allows frequencies outside this range to pass.

Q6b) iii. Sketch graphs for each of the filters named above.
(As an AI, I cannot directly sketch graphs. Below are descriptions of the typical frequency response graphs for each filter type, showing Gain vs. Frequency.)

• Low-pass filter: The graph shows high gain (passband) for low frequencies, which then gradually decreases (rolls off) to low gain (stopband) as frequency increases beyond the cutoff frequency.
• High-pass filter: The graph shows low gain (stopband) for low frequencies, which then gradually increases (rolls off) to high gain (passband) as frequency increases beyond the cutoff frequency.
• Band-pass filter: The graph shows low gain for very low frequencies, rises to high gain within a specific frequency range (passband), and then drops back to low gain for very high frequencies.
• Band-stop filter: The graph shows high gain for very low frequencies, drops to low gain within a specific frequency range (stopband), and then rises back to high gain for very high frequencies.

Q7) With reference to satellite communication, briefly explain the following:

• i. Inclined elliptical orbit: An orbit that is not perfectly circular and whose orbital plane is tilted at an angle relative to the Earth's equatorial plane. Satellites in such orbits experience varying altitude and speed, allowing them to cover different geographical regions over time.
• ii. Polar circular orbit: A circular orbit that passes over or very close to both the North and South poles of the Earth. Satellites in these orbits typically maintain a constant altitude and provide global coverage over several passes as the Earth rotates beneath them.
• iii. Geostationary orbit: A specific type of geosynchronous orbit that is circular and lies directly above the Earth's equator (0° latitude). A satellite in this orbit has an orbital period exactly equal to the Earth's rotational period, making it appear stationary from the ground, which is ideal for continuous communication to a fixed region.

Q8) State the uses of the following fault-finding equipment:

• i. Signal tracer: Used to follow the path of an electrical signal through an electronic circuit, helping to identify points where the signal is lost, distorted, or interrupted, thereby pinpointing faulty components or sections.
• ii. Non-magnetic screwdriver: Used in electronics repair, especially when working with magnetic components (like speakers, hard drives) or sensitive circuits, to prevent accidental magnetization of components or interference with existing magnetic fields.
• iii. Signal generator: Used to produce various types of electrical signals (e.g., sine waves, square waves, pulses) at controlled frequencies and amplitudes. These signals are injected into circuits to test their response, troubleshoot issues, and measure performance.

Q9) The instantaneous voltage of a frequency-modulated wave is given by: $V = 30 \sin (10\pi t + \cos 5000t) \text{ V}$
Calculate:
i. Modulation index
ii. Carrier frequency
iii. Frequency deviation

The general form of an FM wave is $V(t) = A_c \sin(\omega_c t + m_f \cos(\omega_m t))$.
Comparing the given equation $V = 30 \sin (10\pi t + \cos 5000t) \text{ V}$ with the general form:
$A_c = 30 \text{ V}$
$\omega_c = 10\pi \text{ rad/s}$
The phase deviation term is $m_f \cos(\omega_m t) = \cos 5000t$.

i. Modulation index ($m_f$)

Comparing $\cos 5000t$ with $m_f \cos(\omega_m t)$, the coefficient of $\cos 5000t$ is 1.
Therefore, the modulation index $m_f = 1$.
The modulation index is $\boxed{\text{1}}$.

ii. Carrier frequency ($f_c$)

From the equation, $\omega_c = 10\pi \text{ rad/s}$.

The carrier frequency is $\boxed{\text{5 Hz}}$.

iii. Frequency deviation ($\Delta f$)

From the phase deviation term $\cos 5000t$, we have $\omega_m = 5000 \text{ rad/s}$.

The frequency deviation is $\boxed{\text{795.77 Hz}}$.