Communication Systems — Flashcards
NIOS · Class 12 · Physics
30 flashcards for Communication Systems (NIOS Class 12 Physics) to test yourself on key terms and facts. Sample: "State the three essential elements"
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State the three essential elements of a communication system.
Answer
1. TRANSMITTER – Converts information into electrical signal and launches it. 2. MEDIUM / CHANNEL – Carries the signal over long distances (e.g., air, cable, fibre). 3. RECEIVER – Intercepts the signa…
Distinguish between Analogue and Digital signals. Give one example of each.
Answer
ANALOGUE SIGNAL: • Varies continuously with time. • Can take any value between min and max. • Example: Human speech (sound waves). DIGITAL SIGNAL: • Takes only discrete values (ON = 1, OFF = 0). • Re…
A radio wave has a frequency of 30 MHz. Calculate its wavelength in free space. (Speed of light c = 3 × 10⁸ m/s)
Answer
Given: ν = 30 MHz = 30 × 10⁶ Hz, c = 3 × 10⁸ m/s Find: Wavelength (λ) Formula: c = νλ → λ = c/ν Step 1: λ = (3 × 10⁸) / (30 × 10⁶) Step 2: λ = (3 × 10⁸) / (3 × 10⁷) Step 3: λ = 10 m Answer: λ = 10 …
What is signal bandwidth? How is it expressed differently for analogue and digital signals?
Answer
BANDWIDTH = The range of frequencies that a signal occupies. For ANALOGUE signals: • Measured in Hz (hertz) • Represents the frequency range of the signal • Example: Human speech = 200 Hz to 4000 Hz …
The VHF band covers 30 MHz to 300 MHz. Calculate the wavelength range of VHF waves in vacuum. (c = 3 × 10⁸ m/s)
Answer
Given: ν₁ = 30 MHz = 3 × 10⁷ Hz, ν₂ = 300 MHz = 3 × 10⁸ Hz Find: Wavelength range Formula: λ = c/ν For ν₁ = 30 MHz: λ₁ = (3 × 10⁸) / (3 × 10⁷) = 10 m For ν₂ = 300 MHz: λ₂ = (3 × 10⁸) / (3 × 10⁸) = …
Why is modulation necessary for long-distance signal transmission? Give TWO reasons.
Answer
Modulation is needed because low-frequency audio signals CANNOT be transmitted directly over long distances. Reasons: 1. ANTENNA SIZE PROBLEM: • Antenna size must be comparable to wavelength (λ/4). •…
State the formula for an Amplitude Modulated (AM) wave. Define the modulation index (mₐ).
Answer
AM WAVE FORMULA: v_mod(t) = V_c₀ [1 + mₐ sin(ωₐt)] sin(ωct) Where: • V_c₀ = Amplitude of carrier wave • ωc = Angular frequency of carrier • ωₐ = Angular frequency of audio (modulating) signal • mₐ = …
An AM wave has a carrier wave of amplitude 5V and the audio signal has amplitude 2V. Calculate the modulation index.
Answer
Given: V_c₀ = 5 V (carrier amplitude), V_a₀ = 2 V (audio amplitude) Find: Modulation index (mₐ) Formula: mₐ = V_a₀ / V_c₀ Step 1: mₐ = 2 / 5 Step 2: mₐ = 0.4 Answer: mₐ = 0.4 (or 40% modulation) S…
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