intro
MCQs 1:
In a real-world transformer, the power output is:
Topic: Electrical Power in Transformers
Correct Answer: C) Less than the power input
- An ideal transformer, which exists only in theory, would have Power Input equal to Power Output because it would lack any power losses.
- However, in actual transformers, there are inevitable power losses due to reasons like resistance of the windings, magnetic losses in the core, and leakage flux.
- Hence, the power output in a real-world transformer is invariably less than the power input.
MCQs 2:
Which option refers to electromagnetic waves?
Topic: Electromagnetic Spectrum
Correct Answer: D) All of the above
- Electromagnetic waves encompass a broad range of wavelengths and frequencies, including infra-red, visible light, and microwaves.
- These are all forms of electromagnetic radiation that differ primarily in their wavelengths.
- So, the correct answer is D, "All of the above".
MCQs 3:
An alternating voltage is expressed as E = 141 sin (628t). What are the R.M.S value and the frequency of this voltage, respectively?
Topic: Alternating Current and Voltage
Correct Answer: C) 100 V, 100 Hz
- In alternating current theory, the RMS value is obtained by dividing the peak value by the square root of 2. So, Erms = E0/√2 = 141/1.41 = 100V.
- The frequency is determined by dividing ω by 2π. Hence, v = ω/2π = 628/(2×3.14) = 100Hz.
- Thus, the correct answer is C, "100 V, 100 Hz".
Question 4:
What is the r.m.s value of an A.C. current?
Topic: RMS Value of Alternating Current
Correct Answer: B) 0.7 I0
- The RMS (Root Mean Square) value of an alternating current is the effective value or the equivalent DC value that would produce the same power in a resistor.
- This value is given by 0.7 times the peak current (I0).
- Therefore, the correct answer is B, "0.7 I0".
Question 5:
What is the power factor value in an LCR circuit at resonance?
Topic: Resonance in LCR Circuits
Correct Answer: C) 1
- In an LCR circuit at resonance, the inductive reactance and capacitive reactance are equal, which cancels each other out.
- This leaves only the resistance, making the phase angle zero.
- As the power factor is the cosine of the phase angle, at resonance (where the phase angle is zero), the power factor is cos(0) = 1.
- Hence, the correct answer is C, "1".
Question 6:
What happens to the reactance of an inductor if the frequency of the alternating current passing through it is increased?
Topic: Inductive Reactance in AC Circuits
Correct Answer: A) Increases
- The inductive reactance (XL) is given by the formula XL = 2πfL, where f is the frequency and L is the inductance.
- As the formula indicates, the inductive reactance is directly proportional to the frequency.
- Therefore, when the frequency of the AC increases, the inductive reactance also increases.
- Thus, the correct answer is A, "Increases".
MCQs 7:
Where are electrical oscillators primarily used?
Topic: Applications of Electrical Oscillators
Correct Answer: A) Metal detectors
- Electrical oscillators generate alternating currents or voltages, which find usage in many devices.
- One of the key applications is in metal detectors, where oscillators help generate the magnetic field needed to detect metal objects.
- Hence, the correct answer is A, "Metal detectors".
MCQs 8:
What is the average value of alternating current over an entire cycle?
Topic: Mean Value of Alternating Current
Correct Answer: C) Zero
- Alternating current (AC) has an equal number of positive and negative half cycles.
- During the positive half cycle, the current flows in one direction, and during the negative half cycle, it flows in the opposite direction.
- When these are added up over a complete cycle, they cancel each other out, resulting in a mean or average value of zero.
- Thus, the correct answer is C, "Zero".
MCQs 9:
What term is used to describe the inverse of impedance?
Topic: Impedance and Its Reciprocal
Correct Answer: C) Admittance
- Impedance is a measure of opposition to alternating current (AC).
- Its reciprocal, meaning one divided by the impedance, is called admittance.
- Admittance represents how easily an AC circuit allows current to flow.
- Therefore, the correct answer is C, "Admittance".
Question 10:
If an AC source of 220V, 50Hz is connected to a coil and the coil draws a current of 2A and consumes 200W power, what would the inductance of the coil be?
Topic: Inductance Calculation in AC Circuits
Correct Answer: C) 0.3 H
- The inductive reactance (XL) can be calculated using the formula: XL = V/I, where V is the voltage and I is the current.
- Once XL is known, the inductance (L) can be calculated from the formula: L = XL/(2πf), where f is the frequency.
- In this case, the inductance comes out to be 0.3 H.
- Hence, the correct answer is C, "0.3 H".
Question 11:
The given phasor diagram corresponds to which type of circuit configuration?
Topic: Identifying Circuits from Phasor Diagrams
Correct Answer: D) RLC series circuit
- A phasor diagram represents the phase relationships between different components in an AC circuit.
- The given phasor diagram shows the presence of resistance (R), inductance (L), and capacitance (C), which suggests an RLC series circuit.
- In an RLC series circuit, the total impedance is the vector sum of resistance, inductive and capacitive reactance.
- Hence, the correct answer is D, "RLC series circuit".
Question 12:
What will be the effect on inductive reactance if the frequency of the alternating current is doubled?
Topic: Effect of Frequency on Inductive Reactance
Correct Answer: C) Doubled
- The inductive reactance (XL) is given by the equation XL = 2πfL, where f is the frequency and L is the inductance.
- This equation suggests a direct proportional relationship between the frequency and inductive reactance.
- Therefore, if the frequency is doubled, the inductive reactance will also double.
- So, the correct answer is C, "Doubled".
MCQ 13:
What would be the frequency of an AC wave with a time period of 5 seconds?
Topic: Determining Frequency from Time Period
Correct Answer: D) 0.2 Hz
- The frequency (f) of an AC wave is the reciprocal of its time period (T), i.e., f = 1/T.
- In this case, the time period is given as 5 seconds.
- Therefore, the frequency would be 1/5 = 0.2 Hz.
- Thus, the correct answer is D, "0.2 Hz".
MCQ 14:
What is the standard unit for measuring impedance?
Topic: Unit of Impedance
Correct Answer: D) Ohm
- Impedance, in the field of electricity, is a measure of the opposition that a circuit presents to the flow of current.
- It has both magnitude and phase, unlike resistance, which has only magnitude.
- The SI unit of impedance is the same as that of resistance, namely, Ohm.
- Therefore, the correct answer is D, "Ohm".
MCQ 15:
When a coil with an inductance of 0.03 henry is connected to a 200-volt DC supply, a stable current of 20 A flows through it. What would be the power factor for a 50 Hz AC supply?
Topic: Power Factor in AC Circuits
Correct Answer: D) 0.7
- The power factor in an AC circuit is the ratio of real power (P) to apparent power (S), and indicates the phase difference between voltage and current.
- A power factor of 1 indicates that voltage and current are in phase, meaning all the power is effectively used.
- In this case, the given conditions correspond to a power factor of 0.7.
- Thus, the correct answer is D, "0.7".
MCQs 16:
Which options listed below are considered to be electromagnetic waves?
Topic: Types of Electromagnetic Waves
Correct Answer: D) All of the above
- Electromagnetic waves include a wide range of wave types such as infra-red waves, visible light, and microwaves.
- All the options listed in this question fall under the category of electromagnetic waves.
- Therefore, the correct answer is D, "All of the above".
MCQs 17:
What is the phase difference between the voltage and the current in an inductor?
Topic: Phase Difference in an Inductor
Correct Answer: A) The current is behind the voltage by 90°
- In an inductor, the current lags behind the voltage by 90° due to inertia.
- Therefore, the correct answer is A, "The current is behind the voltage by 90°".
MCQs 18:
What does an A.C depend on as a function?
Topic: Dependence of A.C
Correct Answer: D) Time
- An AC current varies as a function of time, following the equation V = V0 sin (2πft).
- Time (t) is the only variable in this equation.
- Therefore, the correct answer is D, "Time".
MCQs 19:
How many times does an A.C reach its peak value in each cycle?
Topic: AC Cycle Peaks
Correct Answer: B) Twice
- A sinusoidal wave like AC current reaches its peak value twice in each cycle.
- It reaches the maximum positive value and the maximum negative value in each cycle.
- Therefore, the correct answer is B, "Twice".