CUET UG Physics Booster Test 2-Foundations of Alternating Current
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QUESTION 1 OF 20
The AC voltage in an electrical mains supply
1. varies like a sine function with time
2. can be efficiently converted using transformers
3. does not change direction with time
4. is entirely equivalent to a pure battery source
QUESTION 2 OF 20
Choose the incorrect statement about AC current driven by an AC voltage:
QUESTION 3 OF 20
Consider the statements on sinusoidal function properties. Choose the correct statements:
1. The sum of instantaneous values over one complete cycle is zero
2. The voltage and current in a pure resistor reach zero at the same time
3. The average value of sine squared over a cycle is zero
4. The instantaneous value is time-dependent
QUESTION 4 OF 20
When calculating the instantaneous current in a purely inductive circuit driven by v = vm sin(ωt), the integration constant evaluates to zero because:
QUESTION 5 OF 20
In a purely resistive AC circuit, the voltage amplitude
QUESTION 6 OF 20
Match List I with List II:
| List I | List II |
|---|---|
| 1. Peak current im | a. vm / R |
| 2. Instantaneous current i | b. Zero |
| 3. RMS current I | c. im / √2 |
| 4. Average current over a cycle | d. im sin(ωt) |
QUESTION 7 OF 20
Choose the correct statements about effective voltage:
1. It is also called root mean square voltage
2. It is equal to 0.707 vm
3. It is customarily used to measure and specify AC quantities like household line voltage
4. It is fundamentally twice the peak voltage
QUESTION 8 OF 20
If the rms voltage across a resistor is 100 V, what will be the peak voltage of the source?
QUESTION 9 OF 20
The root mean square (rms) current in an AC circuit is,
1. is mathematically defined as im / √2
2. produces the same average power loss as an equivalent DC current
3. is strictly equal to the peak current
4. is always zero over a complete cycle
Choose correct:
QUESTION 10 OF 20
To express AC power in the same formulaic form as DC power (P = I²R), what specific value of the alternating current is utilized?
QUESTION 11 OF 20
Voltage and current quantities in an AC circuit, and the mathematical way they combine using phasors are respectively:
QUESTION 12 OF 20
In the application of phasor diagrams to an AC circuit,
QUESTION 13 OF 20
Match List I with List II regarding terms in v = vm sin(ωt)
| List I | List II |
|---|---|
| 1. ω | a. Time instant |
| 2. t | b. Voltage amplitude |
| 3. ωt | c. Phase angle parameter |
| 4. vm | d. Angular frequency |
QUESTION 14 OF 20
Choose the incorrect statement about phase angle in a purely resistive AC circuit:
QUESTION 15 OF 20
Consider the statements on Nikola Tesla contributions. Choose the correct statements.
1. He conceived the idea of the rotating magnetic field
2. He invented the induction motor
3. He opposed the use of alternating current
4. He invented the high frequency induction coil
QUESTION 16 OF 20
Choose the correct statements about George Westinghouse:
1. He was a leading proponent of alternating current over direct current
2. He enlisted the services of Nikola Tesla and other inventors
3. He advocated direct current alongside Thomas Edison
4. He pioneered in large scale lighting utilizing AC
QUESTION 17 OF 20
The primary device for AC voltage conversion and the fundamental principle it prominently utilises:
QUESTION 18 OF 20
If an ideal step-up transformer at a power station changes a 220 V input at 10 A to an output of 440 V, what will be the output current transmitted over the long distance?
QUESTION 19 OF 20
When AC voltage is applied to a pure resistor, the sum of the instantaneous current values over one complete cycle is zero. This functionally implies that:
QUESTION 20 OF 20
The current in a pure resistor driven by an AC voltage
1. varies sinusoidally
2. has corresponding positive and negative values during each cycle
3. strictly lags the applied voltage by π/2
4. has an average value of zero over one cycle
Choose the correct options:
Test Complete!
Answer Review
1 The AC voltage in an electrical mains supply
1. varies like a sine function with time
2. can be efficiently converted using transformers
3. does not change direction with time
4. is entirely equivalent to a pure battery source
�� AC voltage varies sinusoidally with time. �� Transformers work efficiently only with AC. �� AC reverses polarity periodically.
Alternating voltage is represented by: v = vm sin(ωt) Hence statement 1 is correct because AC voltage varies sinusoidally with time. Statement 2 is also correct because transformers operate on mutual induction and can efficiently step up or step down AC voltages. Statement 3 is incorrect because AC changes direction periodically. Statement 4 is incorrect because a battery supplies DC, whereas AC continuously changes magnitude and direction. Therefore statements 1 and 2 are correct.
- �� Option B → Statement 3 is incorrect because AC changes direction periodically.
- �� Option C → Statements 3 and 4 are both incorrect.
- �� Option D → Statement 4 is incorrect because AC is not equivalent to a battery source.
Used
- Elimination
Application:
- Identify statements that contradict the basic definition of alternating current.
Final Logic:
- Only statements 1 and 2 correctly describe AC voltage.
AC = Alternates + Converts
2 Choose the incorrect statement about AC current driven by an AC voltage:
�� AC reverses direction periodically. �� AC is produced by alternating voltage. �� Sinusoidal AC varies harmonically with time.
Alternating current continuously changes both magnitude and direction with time. Therefore statement B is incorrect. Statements A, C, and D correctly describe AC current. AC is produced by alternating voltage sources and usually varies sinusoidally with time.
- �� Option A → Correct property of AC current.
- �� Option C → AC is the standard form of electrical power supply.
- �� Option D → Sinusoidal variation is a basic feature of AC.
Used
- Odd One Out
Application:
- Find the statement that contradicts the definition of AC.
Final Logic:
- Only Option B states that AC does not reverse direction.
AC = Always Changes direction
3 Consider the statements on sinusoidal function properties. Choose the correct statements:
1. The sum of instantaneous values over one complete cycle is zero
2. The voltage and current in a pure resistor reach zero at the same time
3. The average value of sine squared over a cycle is zero
4. The instantaneous value is time-dependent
�� Average value of sine over a cycle is zero. �� Voltage and current are in phase in a resistor. �� Average value of sin²θ is 1/2.
Statement 1 is correct because positive and negative halves of a sine wave cancel over a complete cycle. Statement 2 is correct because voltage and current are in phase in a pure resistor and therefore reach maxima, minima, and zero simultaneously. Statement 3 is incorrect because: Average value of sin²θ = 1/2 not zero. Statement 4 is correct because instantaneous voltage and current depend on time. Hence statements 1, 2, and 4 are correct.
- �� Option B → Includes incorrect statement 3.
- �� Option C → Includes incorrect statement 3.
- �� Option D → Includes incorrect statement 3.
Used
- Elimination
Application:
- Check each statement using standard sinusoidal properties.
Final Logic:
- Only statement 3 is false.
sin² average = 1/2
4 When calculating the instantaneous current in a purely inductive circuit driven by v = vm sin(ωt), the integration constant evaluates to zero because:
�� AC source has no DC offset. �� Positive and negative halves are symmetric. �� Integration constant becomes zero.
While integrating the voltage equation for a pure inductor, an integration constant appears. Since the source voltage oscillates symmetrically about zero and has no constant DC component, the integration constant must be zero. The remaining options do not affect the value of the integration constant.
- �� Option B → Resistance does not determine the integration constant.
- �� Option C → Time being an independent variable is unrelated.
- �� Option D → Power loss does not affect the integration constant.
Used
- Elimination
Application:
- Remove options unrelated to the mathematical integration process.
Final Logic:
- Symmetry about zero ensures zero integration constant.
Pure AC → Zero Offset
5 In a purely resistive AC circuit, the voltage amplitude
�� Ohm's law applies to AC resistor circuits. �� Voltage and current remain in phase. �� Peak values satisfy im = vm/R.
For a pure resistor: v = iR Using peak values: vm = imR Therefore: im = vm/R Hence voltage amplitude determines current amplitude. RMS voltage is not equal to peak voltage. The phase angle remains zero and voltage amplitude is not zero.
- �� Option B → RMS voltage equals vm/√2.
- �� Option C → Phase difference remains zero.
- �� Option D → Voltage amplitude is the maximum value, not zero.
Used
- Substitution
Application:
- Apply Ohm's law directly to peak values.
Final Logic:
- im = vm/R directly proves Option A.
Peak V ÷ R = Peak I
6 Match List I with List II:
| List I | List II |
|---|---|
| 1. Peak current im | a. vm / R |
| 2. Instantaneous current i | b. Zero |
| 3. RMS current I | c. im / √2 |
| 4. Average current over a cycle | d. im sin(ωt) |
�� Peak current = vm/R. �� Instantaneous current = im sin(ωt). �� RMS current = im/√2. �� Average current over a cycle = 0.
1 → a because im = vm/R 2 → d because i = im sin(ωt) 3 → c because I = im/√2 4 → b because average AC current over one complete cycle is zero. Therefore: 1-a, 2-d, 3-c, 4-b
- �� Option B → Incorrect mapping of all major quantities.
- �� Option C → Peak and instantaneous current are interchanged.
- �� Option D → RMS and instantaneous current are incorrectly matched.
Used
- Option Grouping
Application:
- Match standard AC expressions with their definitions.
Final Logic:
- Only Option A gives all four correct pairings.
Peak–Instant–RMS–Average = V/R–Sin–√2–Zero
7 Choose the correct statements about effective voltage:
1. It is also called root mean square voltage
2. It is equal to 0.707 vm
3. It is customarily used to measure and specify AC quantities like household line voltage
4. It is fundamentally twice the peak voltage
�� Effective voltage means RMS voltage. �� RMS voltage equals 0.707 Vm. �� Household voltage ratings use RMS values.
Statement 1 is correct because effective voltage and RMS voltage are the same. Statement 2 is correct because: Vrms = Vm/√2 = 0.707Vm Statement 3 is correct because domestic supply voltages are specified using RMS values. Statement 4 is incorrect because RMS voltage is smaller than peak voltage.
- �� Option B → Includes incorrect statement 4.
- �� Option C → Includes incorrect statement 4.
- �� Option D → Includes incorrect statement 4.
Used
- Elimination
Application:
- Use RMS relations to verify each statement.
Final Logic:
- Only statement 4 is false.
RMS = 70.7% of Peak
8 If the rms voltage across a resistor is 100 V, what will be the peak voltage of the source?
�� RMS and peak values differ. �� Vm = √2 Vrms. �� √2 ≈ 1.414.
Given: Vrms = 100 V Peak voltage: Vm = √2 × 100 Vm = 141.4 V Therefore the peak voltage is 141.4 V.
- �� Option A → Less than RMS value.
- �� Option C → Calculation error.
- �� Option D → RMS and peak values are not equal.
Used
- Substitution
Application:
- Substitute the given RMS value into the standard formula.
Final Logic:
- Vm = 1.414 × 100 = 141.4 V.
Peak = 1.414 × RMS
9 The root mean square (rms) current in an AC circuit is,
1. is mathematically defined as im / √2
2. produces the same average power loss as an equivalent DC current
3. is strictly equal to the peak current
4. is always zero over a complete cycle
Choose correct:
�� RMS current equals im/√2. �� RMS value gives DC-equivalent heating effect. �� RMS current is not zero.
Statement 1 is correct because: Irms = im/√2 Statement 2 is correct because RMS current is defined as the value of DC current producing the same average power loss in a resistor. Statement 3 is incorrect because RMS current is less than peak current. Statement 4 is incorrect because RMS current has a finite positive value. Therefore statements 1 and 2 are correct.
- �� Option B → Statement 3 is incorrect.
- �� Option C → Both statements are incorrect.
- �� Option D → Statement 4 is incorrect.
Used
- Elimination
Application:
- Use RMS definition and heating effect concept.
Final Logic:
- Only statements 1 and 2 are correct.
RMS = Heating Equivalent DC
10 To express AC power in the same formulaic form as DC power (P = I²R), what specific value of the alternating current is utilized?
�� RMS current gives equivalent heating effect. �� AC power calculations use RMS values. �� Average current over a cycle is zero.
The average power dissipated in a resistor carrying alternating current is: P = I²R where I represents the RMS current. The RMS value is chosen because it produces the same heating effect as an equivalent DC current. Therefore AC power expressions can be written in the same form as DC power expressions.
- �� Option A → Changes continuously with time.
- �� Option B → Does not represent average heating effect.
- �� Option C → Average AC current over a cycle is zero.
Used
- Contextual/Tonal Matching
Application:
- Identify the quantity that makes AC and DC power formulas equivalent.
Final Logic:
- RMS current uniquely represents DC-equivalent power dissipation.
Power Uses RMS
11 Voltage and current quantities in an AC circuit, and the mathematical way they combine using phasors are respectively:
�� Voltage and current are scalar physical quantities. �� Phasors provide a vector-like representation. �� Phasor addition follows vector rules.
Voltage and current possess magnitude but no spatial direction; hence they are scalar quantities. However, AC voltages and currents are conveniently represented by rotating vectors called phasors. The addition and subtraction of phasors follow vector algebra. Therefore: Voltage and current → Scalar Phasor combination → Vectorial Hence Option A is correct.
- �� Option B → Voltage and current are not vector quantities.
- �� Option C → Phasor addition is vectorial, not scalar.
- �� Option D → Voltage and current are scalars.
Used
- Conceptual Classification (Odd One Out)
Application:
- Separate physical quantities from their mathematical representation.
Final Logic:
- Quantities are scalar, but phasor operations are vectorial.
Physical Scalar, Phasor Vector
12 In the application of phasor diagrams to an AC circuit,
�� Phasors rotate with angular velocity ω. �� Vertical projection gives instantaneous value. �� Phasor length gives amplitude.
In phasor representation, voltage and current are shown as rotating vectors. The instantaneous values are obtained from the vertical projection of the rotating phasors. Thus: v = vertical component of V i = vertical component of I Hence Option B is correct.
- �� Option A → Instantaneous values are represented by vertical components.
- �� Option C → Phasor length represents amplitude, not instantaneous value.
- �� Option D → Reference axes are fixed while phasors rotate.
Used
- Elimination
Application:
- Compare each statement with standard phasor-diagram conventions.
Final Logic:
- Only vertical projections represent instantaneous sinusoidal values.
Vertical Projection = Instantaneous Value
13 Match List I with List II regarding terms in v = vm sin(ωt)
| List I | List II |
|---|---|
| 1. ω | a. Time instant |
| 2. t | b. Voltage amplitude |
| 3. ωt | c. Phase angle parameter |
| 4. vm | d. Angular frequency |
�� ω denotes angular frequency. �� t denotes time. �� ωt represents phase angle. �� vm denotes maximum voltage.
In v = vm sin(ωt) 1 → d because ω is angular frequency. 2 → a because t is time. 3 → c because ωt represents phase angle. 4 → b because vm is voltage amplitude. Therefore: 1-d, 2-a, 3-c, 4-b
- �� Option B → Incorrectly assigns ω and vm.
- �� Option C → Interchanges time and phase angle.
- �� Option D → Multiple mismatches.
Used
- Option Grouping
Application:
- Match each symbol with its physical meaning.
Final Logic:
- Only Option A gives all correct correspondences.
ω-Time-Phase-Peak
14 Choose the incorrect statement about phase angle in a purely resistive AC circuit:
�� In a resistor, voltage and current are in phase. �� Phase difference equals zero. �� Maxima occur simultaneously.
For a pure resistor: v = Vm sin(ωt) i = Im sin(ωt) Both quantities have identical phase. Therefore phase angle is zero. Statements A, B and D are correct. Statement C is incorrect because a phase difference of π/2 occurs in pure inductive or capacitive circuits, not in a pure resistor.
- �� Option A → Correct property of a pure resistor.
- �� Option B → Current and voltage peak simultaneously.
- �� Option D → Phasors remain aligned.
Used
- Odd One Out
Application:
- Identify the statement inconsistent with in-phase behavior.
Final Logic:
- Only Option C introduces a non-zero phase difference.
Resistor = Zero Phase
15 Consider the statements on Nikola Tesla contributions. Choose the correct statements.
1. He conceived the idea of the rotating magnetic field
2. He invented the induction motor
3. He opposed the use of alternating current
4. He invented the high frequency induction coil
�� Tesla pioneered AC technology. �� Invented induction motor. �� Developed Tesla coil.
Statement 1 is correct because Tesla developed the rotating magnetic field concept. Statement 2 is correct because he invented the induction motor. Statement 4 is correct because he developed the high-frequency induction coil known as the Tesla coil. Statement 3 is incorrect because Tesla strongly supported alternating current. Hence statements 1, 2 and 4 are correct.
- �� Option A → Includes incorrect statement 3.
- �� Option C → Includes incorrect statement 3.
- �� Option D → Includes incorrect statement 3.
Used
- Elimination
Application:
- Remove the historically incorrect statement.
Final Logic:
- Tesla supported AC, making statement 3 false.
Tesla = AC + Motor + Coil
16 Choose the correct statements about George Westinghouse:
1. He was a leading proponent of alternating current over direct current
2. He enlisted the services of Nikola Tesla and other inventors
3. He advocated direct current alongside Thomas Edison
4. He pioneered in large scale lighting utilizing AC
�� Westinghouse promoted AC systems. �� Worked with Tesla. �� Helped establish large-scale AC distribution.
Statements 1, 2 and 4 are historically correct. Westinghouse became a major supporter of AC power systems, collaborated with Tesla, and promoted large-scale AC transmission and lighting projects. Statement 3 is incorrect because Thomas Edison supported DC, whereas Westinghouse promoted AC.
- �� Option A → Includes incorrect statement 3.
- �� Option C → Includes incorrect statement 3.
- �� Option D → Includes incorrect statement 3.
Used
- Elimination
Application:
- Identify the statement conflicting with AC history.
Final Logic:
- Westinghouse supported AC, not DC.
Westinghouse = West for AC
17 The primary device for AC voltage conversion and the fundamental principle it prominently utilises:
�� Transformers change AC voltage. �� Mutual induction links two coils. �� Widely used in power transmission.
A transformer operates using mutual induction between primary and secondary windings. Changing current in the primary coil produces changing magnetic flux which induces emf in the secondary coil. Therefore, AC voltage conversion is achieved using transformers based on mutual induction.
- �� Option B → Resistors cannot transform voltage.
- �� Option C → Capacitors store energy but do not perform voltage transformation.
- �� Option D → Self-induction alone is insufficient for transformer action.
Used
- Contextual/Tonal Matching
Application:
- Match the device with its operating principle.
Final Logic:
- Transformer operation fundamentally depends on mutual induction.
Transformer → Mutual Transfer
18 If an ideal step-up transformer at a power station changes a 220 V input at 10 A to an output of 440 V, what will be the output current transmitted over the long distance?
�� Ideal transformer conserves power. �� Input power equals output power. �� Current decreases when voltage increases.
For an ideal transformer: VpIp = VsIs 220 × 10 = 440 × Is 2200 = 440Is Is = 5 A Therefore, output current equals 5 A.
- �� Option A → Would violate power conservation.
- �� Option C → Current must decrease when voltage doubles.
- �� Option D → Impossible under ideal transformer conditions.
Used
- Substitution
Application:
- Apply transformer power relation directly.
Final Logic:
- 220 × 10 = 440 × Is gives Is = 5 A.
Voltage ↑ ⇒ Current ↓
19 When AC voltage is applied to a pure resistor, the sum of the instantaneous current values over one complete cycle is zero. This functionally implies that:
�� Average current over a cycle is zero. �� Heating depends on i²R. �� Positive and negative currents both produce heat.
Although the algebraic sum of current values over one cycle is zero, power dissipation depends on: P = i²R Since i² is always positive, electrical energy continues to be converted into heat during both halves of the cycle. Therefore Joule heating occurs continuously.
- �� Option A → Average power is not zero.
- �� Option B → Heat is continuously produced.
- �� Option D → Current clearly flows through the resistor.
Used
- Odd One Out
Application:
- Distinguish current averaging from power averaging.
Final Logic:
- Heating depends on i², not on the average value of i.
Current Cancels, Heat Doesn't
20 The current in a pure resistor driven by an AC voltage
1. varies sinusoidally
2. has corresponding positive and negative values during each cycle
3. strictly lags the applied voltage by π/2
4. has an average value of zero over one cycle
Choose the correct options:
�� Current follows sinusoidal voltage. �� Positive and negative halves occur. �� Average current over a cycle is zero.
For a pure resistor: i = Im sin(ωt) Hence statement 1 is correct. Statement 2 is correct because sinusoidal current assumes both positive and negative values. Statement 4 is correct because the positive and negative halves cancel over a complete cycle. Statement 3 is incorrect because current and voltage are in phase; there is no phase lag. Therefore statements 1, 2 and 4 are correct.
- �� Option B → Includes incorrect statement 3.
- �� Option C → Includes incorrect statement 3.
- �� Option D → Includes incorrect statement 3.
Used
- Elimination
Application:
- Apply the in-phase property of a pure resistor.
Final Logic:
- Only statement 3 is false.
Pure Resistor = Zero Lag
