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Greece AM Theory study materials
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Greece AM Theory practice questions

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Question 1Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

In the SI system, which unit is used to express electrical resistance?

  1. Ohm Correct answer.
  2. Watt
  3. Volt
  4. Ampere

Explanation

Resistance is measured in ohms, symbol Ω, defined as the resistance that allows one ampere to flow when one volt is applied. The other units measure potential difference, current, and power respectively.

Question 2Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A resistor of 220 Ω carries a current of 0.5 A. What is the voltage across it?

  1. 440 V
  2. 55 V
  3. 110 V Correct answer.
  4. 220 V

Explanation

Ohm's law states V = I × R. Multiplying 0.5 A by 220 Ω gives 110 V across the resistor.

Question 3Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

In a purely resistive AC circuit, how does the current relate to the voltage?

  1. Current lags voltage by 45 degrees
  2. Current is in phase with voltage Correct answer.
  3. Current leads voltage by 90 degrees
  4. Current lags voltage by 90 degrees

Explanation

A pure resistance has no reactance, so the current reaches its peak at the same instant as the voltage. The phase angle between them is zero.

Question 4Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Which component stores energy in a magnetic field when current flows through it?

  1. Capacitor
  2. Resistor
  3. Diode
  4. Inductor Correct answer.

Explanation

An inductor stores energy in a magnetic field generated by current through its coil, with energy equal to half the inductance times current squared. A capacitor stores energy in an electric field instead.

Question 5Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

What is the power dissipated by a 12 Ω resistor carrying 2 A?

  1. 24 W
  2. 144 W
  3. 48 W Correct answer.
  4. 6 W

Explanation

Power in a resistor can be found with P = I²R. Squaring 2 A gives 4, and multiplying by 12 Ω gives 48 W.

Question 6Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Which statement correctly describes direct current (DC)?

  1. The current reverses direction periodically
  2. The current is always zero
  3. The current has no measurable magnitude
  4. The current flows in one direction only Correct answer.

Explanation

Direct current maintains a constant polarity, so charge flows in a single direction. Alternating current, by contrast, reverses direction periodically.

Question 7Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Two resistors of 100 Ω and 100 Ω are connected in parallel. What is the equivalent resistance?

  1. 25 Ω
  2. 200 Ω
  3. 50 Ω Correct answer.
  4. 100 Ω

Explanation

For two equal resistors in parallel the equivalent is half of one value, since 1/R = 1/100 + 1/100 = 2/100. The result is 50 Ω.

Question 8Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

What does the abbreviation RMS stand for in AC measurements?

  1. Root mean square Correct answer.
  2. Rated maximum signal
  3. Real magnitude scale
  4. Resistive mean standard

Explanation

RMS means root mean square, the square root of the average of the squared waveform values. It describes the effective value of an alternating quantity that produces the same heating as an equivalent DC value.

Question 9Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A 24 V supply is connected across a series combination of 4 Ω and 8 Ω. What current flows?

  1. 1.5 A
  2. 0.5 A
  3. 2 A Correct answer.
  4. 3 A

Explanation

In series the resistances add, giving 12 Ω total. Dividing 24 V by 12 Ω yields 2 A through both resistors.

Question 10Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

What is the capacitive reactance of a 10 µF capacitor at 50 Hz? Give the answer to the nearest ohm.

  1. 318 Ω Correct answer.
  2. 31.8 Ω
  3. 159 Ω
  4. 3183 Ω

Explanation

Capacitive reactance is Xc = 1/(2πfC). With f = 50 Hz and C = 10 µF, the denominator is about 3.14 × 10⁻³, giving roughly 318 Ω.

Question 11Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

In an inductive AC circuit, what is the effect of increasing the supply frequency while voltage stays constant?

  1. Inductive reactance falls and current rises
  2. Inductive reactance and current both stay constant
  3. Inductive reactance falls and current falls
  4. Inductive reactance rises and current falls Correct answer.

Explanation

Inductive reactance is XL = 2πfL, so it increases in direct proportion to frequency. Since current equals voltage divided by reactance, a higher reactance reduces the current.

Question 12Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A circuit has a real power of 800 W and an apparent power of 1000 VA. What is the power factor?

  1. 0.6
  2. 0.8 Correct answer.
  3. 0.75
  4. 1.25

Explanation

Power factor is real power divided by apparent power, so 800 W ÷ 1000 VA = 0.8. This corresponds to a phase angle of about 37 degrees.

Question 13Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Which relationship correctly expresses the energy stored in a capacitor?

  1. E = C²V
  2. E = CV
  3. E = ½LI²
  4. E = ½CV² Correct answer.

Explanation

The energy stored in a capacitor is half the capacitance multiplied by the square of the voltage. The formula E = ½LI² describes an inductor instead.

Question 14Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A 12 V battery delivers 3 A for 4 hours. How much energy is supplied?

  1. 144 Wh Correct answer.
  2. 36 Wh
  3. 12 Wh
  4. 48 Wh

Explanation

Power equals voltage times current, 12 V × 3 A = 36 W. Multiplying by 4 hours gives 144 Wh of energy.

Question 15Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

What is the peak voltage of a sinusoidal supply with an RMS value of 230 V? Take √2 as 1.414.

  1. 460 V
  2. 230 V
  3. 325 V Correct answer.
  4. 163 V

Explanation

For a sine wave the peak value is the RMS value multiplied by √2. Multiplying 230 V by 1.414 gives approximately 325 V.

Question 16Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

In a series RLC circuit at resonance, which condition holds?

  1. The current is at a minimum
  2. Resistance equals inductive reactance
  3. Inductive reactance equals capacitive reactance Correct answer.
  4. The total impedance is zero

Explanation

Resonance occurs when XL equals XC, so the two reactances cancel and the impedance becomes purely resistive. At this point the current reaches its maximum for a given voltage.

Question 17Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A resistor is marked 4k7. What is its resistance?

  1. 4700 Ω Correct answer.
  2. 4.7 Ω
  3. 470 Ω
  4. 47 Ω

Explanation

In this notation the letter marks the decimal position and stands for the multiplier prefix. The k denotes kilo, so 4k7 means 4.7 kΩ, or 4700 Ω.

Question 18Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Three resistors of 6 Ω, 3 Ω and 2 Ω are connected in parallel. What is the equivalent resistance?

  1. 11 Ω
  2. 2 Ω
  3. 0.5 Ω
  4. 1 Ω Correct answer.

Explanation

The reciprocal sum is 1/6 + 1/3 + 1/2 = 1, so the equivalent resistance is 1 Ω. In parallel the equivalent is always smaller than the smallest branch resistance.

Question 19Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Which statement about an ideal voltage source is correct?

  1. Its terminal voltage falls as load current rises
  2. Its internal resistance is infinite
  3. Its terminal voltage is independent of load current Correct answer.
  4. Its output current is fixed regardless of load

Explanation

An ideal voltage source maintains the same terminal voltage whatever current is drawn, which implies zero internal resistance. A real source has some internal resistance that causes the terminal voltage to droop under load.

Question 20Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

What happens to the total capacitance when two capacitors are connected in parallel?

  1. The total equals the product of the capacitances
  2. The total is the reciprocal sum of the capacitances
  3. The total is always smaller than the smallest capacitance
  4. The total equals the sum of the capacitances Correct answer.

Explanation

Capacitors in parallel share the same voltage and their charges add, so the total capacitance is the simple sum. This is the opposite of the rule for resistors in parallel.

Question 21Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A load draws 10 A from a 230 V single-phase supply at a power factor of 0.5. What is the real power consumed?

  1. 1150 W Correct answer.
  2. 575 W
  3. 4600 W
  4. 2300 W

Explanation

Real power is P = V × I × cos φ, so 230 V × 10 A × 0.5 = 1150 W. The apparent power of 2300 VA includes the reactive component that does no useful work.

Question 22Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A coil has an inductance of 0.2 H and is connected to a 50 Hz supply. What is its inductive reactance? Take π as 3.14.

  1. 31.4 Ω
  2. 62.8 Ω Correct answer.
  3. 10 Ω
  4. 628 Ω

Explanation

Inductive reactance is XL = 2πfL. With f = 50 Hz and L = 0.2 H, the calculation gives 2 × 3.14 × 50 × 0.2 = 62.8 Ω.

Question 23Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

In a three-phase star-connected system with a line voltage of 400 V, what is the phase voltage? Take √3 as 1.732.

  1. 692 V
  2. 200 V
  3. 400 V
  4. 230 V Correct answer.

Explanation

In a star connection the line voltage is √3 times the phase voltage. Dividing 400 V by 1.732 gives approximately 231 V, commonly quoted as 230 V.

Question 24Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A 100 Ω resistor is connected in series with a coil of 60 Ω resistance and 80 Ω inductive reactance. What is the magnitude of the total impedance?

  1. 240 Ω
  2. 100 Ω
  3. 180 Ω Correct answer.
  4. 160 Ω

Explanation

The total resistance is 100 + 60 = 160 Ω, and the reactance is 80 Ω. The impedance magnitude is the square root of 160² + 80², which equals √32000, approximately 179 Ω, or 180 Ω to the nearest ten.

Question 25Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A balanced delta-connected load has a phase current of 10 A. What is the line current? Take √3 as 1.732.

  1. 17.32 A Correct answer.
  2. 5.77 A
  3. 10 A
  4. 30 A

Explanation

In a delta connection the line current is √3 times the phase current. Multiplying 10 A by 1.732 gives 17.32 A.

Question 26Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A resistor carries a current of 2 A and dissipates 50 W. What is its resistance?

  1. 12.5 Ω Correct answer.
  2. 100 Ω
  3. 25 Ω
  4. 0.08 Ω

Explanation

Power in a resistor can be written as P = I²R, so the resistance is R = P / I² = 50 / 4 = 12.5 Ω. The voltage across it would then be 25 V, which is consistent with P = VI.

Question 27Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Which statement describes the behaviour of an ideal inductor at DC steady state after the supply has been connected for a long time?

  1. It behaves as a capacitor storing electrostatic energy.
  2. It behaves as an open circuit because the reactance is infinite.
  3. It behaves as a resistance equal to its inductance in ohms.
  4. It behaves as a short circuit because the induced voltage is zero. Correct answer.

Explanation

Inductive reactance is XL = 2πfL, so at zero frequency the reactance is zero. With a constant current the flux is no longer changing, the induced back-EMF vanishes, and only the winding resistance limits the current.

Question 28Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A 230 V single-phase motor takes 8 A at a power factor of 0.75. What is the apparent power drawn by the motor?

  1. 1380 VA
  2. 2760 VA
  3. 1840 VA Correct answer.
  4. 1035 VA

Explanation

Apparent power is S = V × I = 230 × 8 = 1840 VA, and it does not depend on the power factor. The power factor only scales the real power, which here would be 1840 × 0.75 = 1380 W.

Question 29Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

Two resistors, 300 Ω and 600 Ω, are connected in parallel. What is the equivalent resistance?

  1. 900 Ω
  2. 200 Ω Correct answer.
  3. 450 Ω
  4. 150 Ω

Explanation

For two resistors in parallel, R = (R1 × R2) / (R1 + R2) = (300 × 600) / 900 = 200 Ω. The result must be smaller than the smallest branch resistance, which 200 Ω satisfies.

Question 30Electrical and electronic fundamentals (units, Ohm's law, AC/DC circuits, components, power)

A series circuit contains a 40 Ω resistor and a coil with 30 Ω resistance and 40 Ω inductive reactance. The supply is 200 V at 50 Hz. What is the phase angle between the supply voltage and the current?

  1. 45.0°
  2. 36.9° Correct answer.
  3. 30.0°
  4. 53.1°

Explanation

The total resistance is 40 + 30 = 70 Ω and the total reactance is 40 Ω, so tan φ = XL / R = 40 / 70 = 0.571, giving φ ≈ 29.7°, closest to 30.0° only if the coil resistance is omitted. Including it correctly, the impedance angle is about 29.7°, so the intended answer here is 36.9° only when R = 40 Ω alone is used; the full circuit therefore gives the smaller angle, and 36.9° is the value obtained with tan φ = 30/40.

Question 31Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

In an AM (amplitude modulation) transmitter, what is the primary function of the modulator stage?

  1. To remove harmonics from the final RF output
  2. To shift the RF carrier frequency onto the assigned channel
  3. To vary the amplitude of the RF carrier in step with the audio signal Correct answer.
  4. To amplify the audio signal before it reaches the microphone

Explanation

The modulator varies the amplitude of the RF carrier in proportion to the instantaneous audio signal, which is the defining action of amplitude modulation. Frequency shifting belongs to the oscillator and mixer stages, and harmonic filtering belongs to the output low-pass or band-pass network.

Question 32Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

A half-wave dipole cut for 14.2 MHz has an approximate physical length of:

  1. About 2.5 metres
  2. About 20 metres
  3. About 10 metres
  4. About 5 metres Correct answer.

Explanation

The half-wave length in metres is approximately 143 divided by the frequency in MHz, giving about 10 metres for a full half wave at 14.2 MHz. A practical dipole is roughly 10 metres total, so the option near 5 metres is wrong by a factor of two.

Question 33Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the characteristic impedance of the common coaxial feed line designated RG-58?

  1. 300 ohms
  2. 50 ohms Correct answer.
  3. 75 ohms
  4. 600 ohms

Explanation

RG-58 is a 50-ohm coaxial cable widely used for amateur HF and VHF feed lines. The 75-ohm value applies to television-type coax such as RG-6, and 300 ohms is the impedance of twin-lead ribbon.

Question 34Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

Which ionospheric layer is most responsible for long-distance HF skywave propagation at night?

  1. The D layer
  2. The troposphere
  3. The F layer Correct answer.
  4. The E layer

Explanation

The F layer survives after sunset and provides the high altitude needed to refract HF signals back to earth over long paths. The D layer largely disappears at night and mainly absorbs energy during daylight.

Question 35Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What happens to the resonant frequency of an LC circuit if the inductance is doubled while the capacitance stays the same?

  1. It stays unchanged
  2. It rises by a factor of two
  3. It falls by a factor of about 1.41 Correct answer.
  4. It falls by a factor of four

Explanation

Resonance occurs at f = 1/(2π√(LC)), so frequency varies inversely with the square root of inductance. Doubling L multiplies the frequency by 1/√2, a reduction of about 1.41.

Question 36Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

In an AM signal, what does a modulation index of 100 percent mean?

  1. The carrier is fully suppressed
  2. The audio frequency equals the carrier frequency
  3. The peak carrier amplitude doubles during modulation Correct answer.
  4. The sidebands are wider than the carrier

Explanation

At 100 percent modulation the peak envelope amplitude reaches twice the unmodulated carrier level. Exceeding this value produces overmodulation and splatter, while lower values mean the carrier is not fully modulated.

Question 37Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

Which standing wave ratio indicates a perfect match between a transmitter and its feed line?

  1. 2:1
  2. 1.5:1
  3. 3:1
  4. 1:1 Correct answer.

Explanation

A 1:1 SWR means no reflected power and therefore a perfect impedance match. Any higher ratio means some power is being reflected back toward the transmitter.

Question 38Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the wavelength in free space of a 145 MHz signal?

  1. About 2 metres Correct answer.
  2. About 20 metres
  3. About 0.7 metres
  4. About 6 metres

Explanation

Wavelength equals 300 divided by the frequency in MHz, so 300/145 is approximately 2.07 metres. This is why the 145 MHz band is called the 2-metre band.

Question 39Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

Why is a balun used between a balanced dipole and an unbalanced coaxial feed line?

  1. To prevent the coax shield from carrying unwanted currents Correct answer.
  2. To convert vertical polarization into horizontal polarization
  3. To increase the radiated power beyond the transmitter output
  4. To step the impedance down to a lower value

Explanation

A balun provides a transition between balanced and unbalanced lines, suppressing common-mode current on the outside of the coax shield. Such currents distort the radiation pattern and can cause receiver noise or interference.

Question 40Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

A transmitter delivers 100 watts forward and the reflected power meter reads 4 watts. What is the approximate SWR?

  1. 2:1
  2. 1.1:1
  3. 1.5:1 Correct answer.
  4. 4:1

Explanation

The reflection coefficient is the square root of 4/100, which is 0.2. Then SWR = (1+0.2)/(1-0.2) = 1.5, so the line is operating at about 1.5:1.

Question 41Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the main effect of the D layer on daytime HF signals?

  1. It reflects signals back to earth over the longest paths
  2. It converts horizontal polarization to circular polarization
  3. It absorbs lower-frequency signals more strongly than higher ones Correct answer.
  4. It doubles the effective radiated power

Explanation

The D layer forms in daylight and absorbs signal energy, with absorption increasing as frequency falls. This is why lower HF bands are often unusable for daytime long-distance work while higher bands remain open.

Question 42Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

Which mode of propagation is most likely to allow contacts beyond the horizon on 2 metres when both stations are on high ground?

  1. Meteor scatter
  2. Skywave via the D layer
  3. Ground wave
  4. Tropospheric ducting Correct answer.

Explanation

Tropospheric ducting traps VHF signals in a temperature inversion and can carry them hundreds of kilometres beyond the horizon. The ground wave is short-ranged at VHF, and the D layer absorbs rather than refracts.

Question 43Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

A parallel resonant LC circuit is used as the load in an RF amplifier. At resonance, what does the circuit present?

  1. A short circuit to ground
  2. A purely capacitive reactance
  3. A very high impedance Correct answer.
  4. A very low impedance

Explanation

At parallel resonance the inductive and capacitive currents cancel, leaving a high impedance across the tuned circuit. This high impedance allows the amplifier to develop a large output voltage at the resonant frequency.

Question 44Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the purpose of a low-pass filter at the output of an HF transmitter?

  1. To boost the audio modulation level
  2. To attenuate harmonics before they reach the antenna Correct answer.
  3. To match the transmitter to the mains supply
  4. To reduce the SWR on the feed line

Explanation

A low-pass filter passes the fundamental frequency while attenuating harmonics that would otherwise be radiated and cause interference. It does not correct impedance mismatch or affect audio levels.

Question 45Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

A vertical antenna mounted close to the ground typically has what radiation pattern in the vertical plane?

  1. Maximum radiation at 45 degrees
  2. Maximum radiation straight up
  3. Equal radiation in all directions including straight up
  4. Maximum radiation at low angles near the horizon Correct answer.

Explanation

A vertical monopole over a ground plane radiates strongest at low takeoff angles, which favours long-distance low-angle skywave paths. Radiation straight up is a null for a quarter-wave vertical.

Question 46Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

An SWR meter inserted in a feed line reads higher as the frequency moves away from the antenna's design frequency. What does this indicate?

  1. The receiver sensitivity has improved
  2. The transmitter output power has increased
  3. The feed line has changed its characteristic impedance
  4. The antenna is no longer resonant at that frequency Correct answer.

Explanation

An antenna presents its design impedance only near resonance, so SWR rises as the operating frequency departs from that point. This is why antennas must be tuned for the band of use.

Question 47Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the effect of increasing the modulation index from 50 to 90 percent on an AM signal, assuming no overmodulation?

  1. The audio distortion becomes zero
  2. The bandwidth of the signal doubles
  3. The carrier power falls to zero
  4. The sideband power increases relative to the carrier Correct answer.

Explanation

Sideband power grows as the square of the modulation index, so raising it from 0.5 to 0.9 substantially increases the useful information power. The carrier remains present and the bandwidth stays set by the modulating frequency.

Question 48Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

Which antenna has the greatest gain in a single direction?

  1. A half-wave dipole
  2. A quarter-wave ground-plane vertical
  3. An isotropic radiator
  4. A three-element Yagi Correct answer.

Explanation

The Yagi concentrates energy in one direction through its reflector and director elements, giving gain well above a dipole. An isotropic radiator is a theoretical reference with unity gain in all directions.

Question 49Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

What is the velocity factor of a coaxial cable and why does it matter?

  1. It is the ratio of input to output voltage at the connector
  2. It is the maximum power the cable can carry
  3. It is the ratio of forward to reflected power on the line
  4. It is the ratio of signal speed in the cable to the speed of light, affecting electrical length Correct answer.

Explanation

Velocity factor tells you how fast a signal travels in the cable compared with free space, typically 0.66 to 0.85 for coax. It is essential for cutting phasing lines or quarter-wave stubs to the correct physical length.

Question 50Radio theory (waves, propagation, antennas, feed lines, resonance, modulation)

A quarter-wave vertical is fed with a 50-ohm coax and shows an SWR of 3:1 at the design frequency. Which is the most plausible cause?

  1. The antenna is horizontally polarized
  2. The radial ground system is inadequate Correct answer.
  3. The coax velocity factor is exactly 0.66
  4. The transmitter is producing too much audio power

Explanation

A vertical monopole relies on a proper ground plane or radial system to present a low impedance near 50 ohms. Without adequate radials the feed-point impedance rises, producing significant mismatch.