intro
MCQs 1:
What is the acceleration of a bar magnet when dropped through a copper ring, given its length is along the axis of the ring?
Topic: Magnetic Field and Lenz's Law in Physics
Correct Answer: B) Less than that due to gravity
- The scenario involves a bar magnet falling through a copper ring, which brings into play Lenz's law of electromagnetic induction.
- According to Lenz's law, the induced electromotive force (EMF) is always in a direction that opposes the change in magnetic flux that caused it.
- Therefore, the induced EMF in the copper ring would oppose the magnetic flux of the falling magnet, which results in a repelling action.
- This repelling action would slow the falling magnet, consequently causing its acceleration to be less than the gravity (g).
- Hence, the correct answer is B, "less than that due to gravity".
MCQs 2:
Which law is signified by the phenomenon where induced currents always create expanding magnetic fields around their conductors that counteract the original magnetic field?
Topic: Electromagnetic Induction in Physics
Correct Answer: A) Lenz's law
- The question refers to the principle of opposing changes in magnetic fields due to induced currents, a concept encapsulated in Lenz's law.
- Named after the Russian scientist Heinrich Lenz who proposed it in 1834, this law plays a key role in understanding the effects of electromagnetic induction.
- Therefore, the correct answer is A, "Lenz's law".
MCQs 3:
Under which condition can we say a transformer is 100% efficient?
Topic: Efficiency in Electrical Transformers
Correct Answer: C) Output power equals Input power
- The problem refers to the operational efficiency of a transformer, which is determined by the proportion of input power converted to output power.
- An ideal transformer, in theory, would have an efficiency of 100%, implying that all input power is transformed to output power with no energy losses.
- Therefore, the correct answer is C, "Output power equals Input power".
Question 4:
What factors can contribute to an increase in the induced electromotive force (EMF)?
Topic: Factors Influencing Induced EMF
Correct Answer: D) All of the above
- The question deals with factors influencing induced EMF, which includes the strength of the magnetic field, the speed of loop motion, and the number of turns in the coil.
- A higher magnetic field strength, faster loop motion, and a greater number of turns in the coil would all cause an increase in induced EMF, according to Faraday's Law of Electromagnetic Induction.
- Hence, the correct answer is D, "All of the above".
Question 5:
What distinguishes the structure and function of AC generators from DC generators?
Topic: Differences between AC and DC Generators
Correct Answer: B) The presence of Commutators in DC generators
- This question is focused on the differences between AC and DC generators.
- While both types of generators have their own unique features, one primary difference lies in the presence of Commutators in DC generators.
- The function of a commutator is to ensure that the current flow in the loop remains unidirectional, irrespective of the coil's position.
- Thus, the correct answer is B, "The presence of Commutators in DC generators".
Question 6:
Why is the core in transformers laminated and separated by insulation?
Topic: Transformer Efficiency and Construction
Correct Answer: C) To decrease eddy currents.
- This question refers to the purpose of laminating the core in transformers.
- By laminating the core and inserting insulation between the layers, eddy currents are effectively reduced.
- Minimizing eddy currents enhances the overall efficiency of the transformer as it decreases energy losses due to heating.
MCQ 7:
What type of energy conversion is performed by a generator?
Topic: Function of Generators
Correct Answer: C) Mechanical energy to electrical energy in both DC and AC generators.
- This question centers on the fundamental function of a generator, whether AC or DC.
- A generator's primary purpose is to convert mechanical energy into electrical energy.
- Regardless of the type (AC or DC), all generators, in principle, perform this function.
- As a result, the correct answer is C, "Mechanical energy to electrical energy in both DC and AC generators."
MCQ 8:
Which law does Lenz's law align with in terms of conservation?
Topic: Application of Lenz's Law
Correct Answer: B) Conservation of energy
- This question is assessing your understanding of Lenz's law and its relationship with other fundamental principles in physics.
- Lenz's law, a part of electromagnetic induction, aligns with the law of conservation of energy.
- It states that the direction of induced current is such that it opposes the change causing it, which ensures energy is conserved.
- Therefore, the correct answer is B, "Conservation of energy".
MCQ 9:
Which type of current effectively powers a step-up transformer?
Topic: Operation of Transformers
Correct Answer: A) Alternating Current (A.C.)
- This question is querying about the type of current that a step-up transformer operates with.
- Step-up transformers function effectively with Alternating Current (AC), not Direct Current (DC).
- Transformers require a changing magnetic field to function, which is provided by AC, not DC.
- Hence, the correct answer is A, "Alternating Current (A.C.)".
MCQ 10:
What is the value of the emf induced in the given circuit?
Topic: Electromagnetic Induction
Correct Answer: A) Zero
- This question is about understanding the concept of electromagnetic induction and induced emf.
- In a circuit where a steady current flows in one coil, a magnetic field is produced in the other coil.
- However, since that magnetic field is not changing, Faraday's law states that there will be no induced voltage in the secondary coil.
- Thus, the correct answer is A, "Zero".
MCQ 11:
What principle explains the negative sign associated with induced electromotive force (e.m.f)?
Topic: Electromagnetic Induction
Correct Answer: B) Lenz's law
- This question tests your understanding of the fundamental principles behind induced e.m.f.
- It is Lenz's law that gives us insight into the negative sign associated with induced e.m.f.
- According to Lenz's law, the induced e.m.f. will always work in a direction to oppose the change that caused it.
- As such, the answer is B, "Lenz's law".
MCQ 12:
The hysteresis loops of a well-functioning transformer are _____________ in size?
Topic: Transformer Efficiency
Correct Answer: A) Small
- This question is checking your knowledge about the impact of hysteresis loops on the efficiency of transformers.
- For a transformer to operate efficiently, the hysteresis loops should ideally be small in size.
- Small hysteresis loops imply that the core of the transformer can magnetize and demagnetize easily, reducing energy waste.
- So, the correct answer is A, "Small".
Question 13:
Which of the following best describes a mobile phone charger?
Topic: Transformers and Rectifiers
Correct Answer: D) Both B and C
- This question is asking you to identify the primary functions of a mobile phone charger.
- A mobile phone charger first acts as a step-down transformer, reducing the voltage from 220 V to a safer 5 V.
- Then, it acts as a rectifier, converting the AC voltage to DC voltage suitable for charging the phone.
- Therefore, the correct answer is D, "Both B and C".
Question 14:
Which of the following utilizes the principle of mutual induction?
Topic: Mutual Induction Usage
Correct Answer: D) Transformer
- This question aims to test your understanding of where mutual induction, a fundamental principle in electromagnetism, is applied.
- The transformer, among the options provided, is the device that operates based on the principle of mutual induction.
- Thus, the correct answer is D, "Transformer".
Question 15:
How is induced e.m.f related to the flux change?
Topic: Induced E.M.F Relation
Correct Answer: B) It is directly proportional to the rate of change in flux.
- This question examines your knowledge of the relationship between induced e.m.f and changes in magnetic flux.
- Induced e.m.f is directly proportional to the rate at which flux changes, not merely its change.
- As a result, the correct answer is B, "It is directly proportional to the rate of change in flux".
MCQs 16:
In an A.C. generator, what effect does increasing the number of coil turns have on the EMF?
Topic: A.C Generator Mechanism
Correct Answer: C) Increases the EMF
- This question probes your understanding of the effect of coil turns in an AC generator on the generated EMF.
- According to the EMF formula for an AC generator, E = NBAω cosωt, the EMF increases with an increase in the number of coil turns.
- Therefore, the correct answer is C, "Increases the EMF".
MCQs 17:
Consider a transformer with an efficiency of 80%. If it receives an input power of 5 kW at a voltage of 200 V, and the voltage at the secondary coil is 250 V, what are the current ratings for the primary and secondary coils respectively?
Topic: Transformer Operations
Correct Answer: C) 25 A and 16 A
- This question tests your understanding of transformer operation involving efficiency, power, and voltage.
- The primary current can be calculated by dividing input power by input voltage, resulting in 25A.
- The output power, considering the 80% efficiency, is 4000W. Divide this by the secondary voltage of 250V to find the secondary current, 16A.
- Thus, the correct answer is C, "25 A and 16 A".
MCQs 18:
What is the frequency of alternating current (A.C.) in Pakistan?
Topic: AC Characteristics
Correct Answer: A) 50Hz
- This question measures your knowledge about specific geographical characteristics of AC power.
- In Pakistan, the standard frequency for AC power is 50Hz.
- Therefore, the correct answer is A, "50Hz".
MCQs 19:
What happens to the induced EMF in an A.C. generator when the angular speed of the coil rotation is doubled?
Topic: AC Generator Functionality
Correct Answer: C) Doubled
- This question assesses your understanding of the relationship between angular speed and induced EMF in an AC generator.
- The induced EMF is directly proportional to the angular speed of rotation. Therefore, if the speed is doubled, the induced EMF will also double.
- This leads us to the correct answer, which is C, "Doubled".
MCQs 20:
In what device does the back electromotive force (e.m.f) occur?
Topic: Electromotive Force
Correct Answer: B) Motor
- This inquiry requires comprehension of the back e.m.f concept and where it occurs.
- The back e.m.f is a phenomenon that is most commonly associated with motors.
- Hence, the correct answer is B, "Motor".
MCQs 21:
What would cause a deflection in a magnetic compass needle when placed nearby?
Topic: Magnetic Fields
Correct Answer: D) Accelerating charge
- This question tests your understanding of the factors that can influence the deflection of a magnetic compass needle.
- Only an accelerating charge can create a magnetic field strong enough to cause a noticeable deflection in a magnetic compass needle.
- Therefore, the correct answer is D, "Accelerating charge".
MCQ 22:
What is the SI unit of the induced electromotive force (emf)?
Topic: Electromotive Force Units
Correct Answer: A) Volt
- This question investigates your knowledge of electromotive force units.
- The SI unit for measuring induced emf is the Volt, which is equivalent to a joule per coulomb.
- Consequently, the correct answer is A, "Volt".
MCQ 23:
What is a consequence of eddy currents in transformers?
Topic: Eddy Currents in Transformers
Correct Answer: B) Core heating
- This query evaluates your understanding of the implications of eddy currents in transformers.
- Eddy currents result in losses due to heating of the transformer's core.
- Therefore, the correct response is B, "Core heating".
MCQ 24:
What is the term used to describe the coil configuration in a generator?
Topic: Generator Coil Arrangement
Correct Answer: C) Armature
- This question investigates your knowledge of the terminology related to generator coil configurations.
- An armature refers to a coil wrapped around a soft iron core, enhancing the strength of the inside magnetic field and keeping it radial to the coil.
- As such, the correct answer is C, "Armature".
MCQs 25:
What type of transformer is usually mounted on a pole in the street to provide electricity to houses?
Topic: Transformer Types
Correct Answer: A) Step-down transformer
- This question assesses your understanding of different types of transformers and their applications.
- Transformers mounted on street poles are generally step-down transformers. They convert the high voltage (commonly 11000 volts) to a lower voltage (220 volts) suitable for home use.
- Therefore, the correct answer is A, "Step-down transformer".
MCQs 26:
Which of the following is stepped up or down by a transformer?
Topic: Function of Transformers
Correct Answer: C) Voltage
- The question aims to evaluate your understanding of the primary function of a transformer.
- Transformers are designed to alter AC voltage levels. A transformer that elevates the voltage from the primary to the secondary coil (more secondary winding turns than primary) is deemed a step-up transformer. Conversely, a transformer purposed to perform the opposite function is a step-down transformer.
- Hence, the correct answer is C, "Voltage".
MCQs 27:
What factors influence the motional emf?
Topic: Factors Influencing Motional EMF
Correct Answer: D) All of the above
- This question examines your knowledge about the dependencies of motional emf.
- The formula for motional emf, Emf = Blv, indicates that it depends on the magnetic field (B), velocity (v), and length (l) of the rod, all of which are perpendicular to each other.
- Thus, the correct answer is D, "All of the above".
MCQs 28:
If a step-up transformer has a primary to secondary coil turn ratio of 1:2 and a Leclanché cell (e.m.f. 1.5V) is connected across the primary coil, what would be the voltage of the secondary coil?
Topic: Transformer Turn Ratio
Correct Answer: A) Zero
- The question assesses your understanding of the operational limitations of transformers.
- Transformers cannot operate with DC power, a critical point to note from the question's statement.
- Therefore, the correct answer is A, "Zero".
MCQs 29:
What law does electromagnetic induction align with in terms of conservation?
Topic: Electromagnetic Induction and Conservation Laws
Correct Answer: B) Conservation of Energy
- This question aims to assess your understanding of the principles that govern electromagnetic induction.
- Electromagnetic Induction, by its nature, adheres to the law of conservation of energy, which states that energy cannot be created or destroyed but can only be transformed from one form to another.
- Accordingly, the answer is B, "Conservation of Energy".
MCQs 30:
Which principle does a transformer operate on?
Topic: Principle of Transformer Operation
Correct Answer: B) Mutual Induction
- This question is designed to test your grasp of the operational principles underlying transformers.
- A transformer operates on the principle of mutual induction, a phenomenon where a change in the current of one coil induces a voltage in a neighboring coil.
- Hence, the correct answer is B, "Mutual Induction".
Question 31:
In relation to electromagnetic waves, what is the speed of light in a vacuum?
Topic: Speed of Light in a Vacuum
Correct Answer: B) 2.998x108 m/s
- This question explores your knowledge of the fundamentals of electromagnetic waves and the speed of light.
- The speed of light in a vacuum is a fundamental constant of nature, approximately 2.998x108 m/s.
- It's essential to have this value at your fingertips as it serves as a benchmark in many physical calculations.
- Therefore, the correct answer is B, "2.998x108 m/s".