intro
MCQs 1:
What is the induced emf in a metallic loop if the rate of change of magnetic flux is 1 wb/s?
Topic: Electromagnetic Induction
Correct Answer: B) 1V
- The induced emf in a loop is equal to the rate of change of magnetic flux, according to Faraday's Law of Electromagnetic Induction.
- Given the rate of change of flux is 1 wb/s, the induced emf is exactly equal to that rate, which is 1V.
- Therefore, the correct answer is B, "1V".
MCQs 2:
When is the induced emf at its maximum if a rectangular wire loop is positioned perpendicular to a uniform magnetic field and then rotated around one of its sides at an "f" frequency?
Topic: Electromagnetic Induction
Correct Answer: A) When the flux is zero
- The induced emf in a loop is at its peak when the change in magnetic flux is maximum, according to Faraday's Law of Electromagnetic Induction.
- In this scenario, the maximum change in flux occurs when the flux is zero, thereby inducing the maximum emf.
- Hence, the correct answer is A, "When the flux is zero".
MCQs 3:
What is the turn ratio of a step-up transformer that is connected to a 220V ac line to provide 22 kV for a neon sign in the secondary circuit, given that a fuse wire in the primary circuit is designed to blow when the current in the secondary circuit exceeds 10mA?
Topic: Transformers
Correct Answer: B) 100
- The turn ratio of a transformer is given by the formula Ns/NP = VS/VP.
- Substituting the given values, we get 22000/220 = 100.
- Therefore, the correct answer is B, "100".
MCQs 4:
What would be the effect on the self-inductance of a coil if its diameter is doubled?
Topic: Electromagnetism
Correct Answer: A) Becomes four times
- The self-inductance of a coil is directly proportional to the square of its diameter.
- Use the formula L = μrn²πd²/2 to determine the effect of doubling the diameter.
- If the diameter is doubled, the self-inductance becomes four times its original value.
MCQs 5:
What is the maximum emf induced by an AC generator with a single turn?
Topic: Alternating Current
Correct Answer: C) ωAB
- For maximum emf in an AC generator with a single turn, use the formula ε = NωABsinθ.
- In this case, consider N=1 and θ=90° to calculate the maximum emf.
- The correct answer is ωAB.
MCQs 6:
Given an AC generator as shown in the image, if side A of the generator is moved inward, in which direction will the emf be induced?
Topic: Electromagnetic Induction
Correct Answer: B) Anticlockwise
- Determine the direction of the induced emf using the right-hand rule.
- In this scenario, the direction on side A is downward, while on side B it is upward, resulting in an anticlockwise direction of the induced emf.
- The correct answer is anticlockwise.
MCQ 7:
What amount of emf is produced in a coil with an area of 0.5m2, if the flux density changes at a rate of 10Wb/m2s?
Topic: Electromagnetic Induction
Correct Answer: C) 5 V
- The emf generated in a coil can be calculated using Faraday's law, with the formula emf = ΔΦ/t or emf = ΔBA/t.
- Given that ΔB/t = 10, the emf produced equals 10 × 0.5 = 5V.
- Hence, the correct answer is C, "5 V".
MCQ 8:
How is induced emf linked to the change in flux?
Topic: Electromagnetic Induction
Correct Answer: B) It's directly proportional to the rate of flux change
- Induced emf is governed by Faraday's law, which states that the induced emf in a circuit equals the negative rate of change of magnetic flux through the circuit.
- Therefore, induced emf is directly proportional to the rate at which the magnetic flux is changing, not simply the flux change.
- Hence, the correct answer is B, "It's directly proportional to the rate of flux change".
MCQ 9:
Consider the scenario where a magnet is falling towards a metallic ring as depicted in the diagram. If one observes the ring from below, which direction will the current in the coil be flowing in?
Topic: Electromagnetic Induction
Correct Answer: A) Clockwise
- As per Lenz's law, the induced current will always oppose the change producing it.
- Therefore, as the magnet falls downward, the face of the coil facing the magnet turns into a north pole.
- Consequently, the side opposite to the magnet becomes the south pole. If the observer is looking from below, they will see the current flowing in a clockwise direction.
- Hence, the correct answer is A, "Clockwise".
Question 10:
In what manner are the primary and secondary coils of a transformer interconnected?
Topic: Transformers
Correct Answer: C) Magnetically
- In a transformer, the primary and secondary coils aren't directly electrically interconnected.
- Instead, these coils are coupled magnetically, with the changing magnetic field of the primary coil inducing a current in the secondary coil.
- Hence, the correct answer is C, "Magnetically".
Question 11:
With which principle of conservation does Lenz's law align?
Topic: Electromagnetic Induction
Correct Answer: C) Conservation of Energy
- Lenz's law, which states that an induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original changing magnetic field, is fundamentally a manifestation of the conservation of energy.
- The law essentially ensures that the energy required to generate an induced current is balanced out by the work done against the change in magnetic field, preserving the total energy.
- Hence, the correct answer is C, "Conservation of Energy".
Question 12:
Which factor does not influence the mutual inductance between the two coils of a transformer?
Topic: Transformers
Correct Answer: D) The current in the primary and secondary coils
- Mutual inductance, symbolized by M, exists between two coils and depends on factors such as the number of turns in both coils and their self-inductances, as well as the separation between the coils.
- However, the current flowing through the coils does not influence the value of M, making it independent of the current.
- Hence, the correct answer is D, "The current in the primary and secondary coils".
Question 10:
In what manner are the primary and secondary coils of a transformer interconnected?
Topic: Transformers
Correct Answer: C) Magnetically
- In a transformer, the primary and secondary coils aren't directly electrically interconnected.
- Instead, these coils are coupled magnetically, with the changing magnetic field of the primary coil inducing a current in the secondary coil.
- Hence, the correct answer is C, "Magnetically".
Question 11:
With which principle of conservation does Lenz's law align?
Topic: Electromagnetic Induction
Correct Answer: C) Conservation of Energy
- Lenz's law, which states that an induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original changing magnetic field, is fundamentally a manifestation of the conservation of energy.
- The law essentially ensures that the energy required to generate an induced current is balanced out by the work done against the change in magnetic field, preserving the total energy.
- Hence, the correct answer is C, "Conservation of Energy".
Question 12:
Which factor does not influence the mutual inductance between the two coils of a transformer?
Topic: Transformers
Correct Answer: D) The current in the primary and secondary coils
- Mutual inductance, symbolized by M, exists between two coils and depends on factors such as the number of turns in both coils and their self-inductances, as well as the separation between the coils.
- However, the current flowing through the coils does not influence the value of M, making it independent of the current.
- Hence, the correct answer is D, "The current in the primary and secondary coils".
Question 16:
What measures are taken to reduce the heating effect in transmission lines?
Topic: Electrical Power Transmission
Correct Answer: C) Applying high voltage with low current
- The power loss in transmission lines due to heating effect is determined by the I2R law, implying that power loss increases with the square of the current.
- Thus, to minimize these losses, the current should be kept as low as possible. This is achieved by using a higher voltage for transmission, which reduces the current (since power = voltage x current).
- Therefore, the correct answer is C, "Applying high voltage with low current".
Question 17:
Which statement accurately describes a step-up transformer?
Topic: Transformers
Correct Answer: C) The current in the secondary coil is lower than the primary coil
- A step-up transformer is designed such that the number of turns in the secondary coil (Ns) is greater than the number of turns in the primary coil (Np), resulting in a higher voltage in the secondary coil (Vs > Vp).
- However, since power must be conserved (Power = Voltage x Current), an increase in voltage results in a corresponding decrease in current. Thus, the current in the secondary coil (Is) is less than the current in the primary coil (Ip).
- Therefore, the correct answer is C, "The current in the secondary coil is lower than the primary coil".
Question 18:
Per Lenz's Law, which component always opposes its cause?
Topic: Electromagnetic Induction
Correct Answer: B) Induced current
- According to Lenz's Law, the direction of the induced current is such that it always opposes the change that caused it.
- Although induced emf initiates the current, it's the direction of the induced current that directly resists the change.
- Consequently, the correct answer is B, "Induced current".
Question 19:
If a sine wave has a frequency of 50Hz, what is its angular velocity in radians per second?
Topic: Wave Motion
Correct Answer: C) 100π rad/s
- Angular velocity (ω) of a wave is calculated as the product of 2π and the frequency of the wave (ω = 2πf).
- Given the frequency is 50Hz, the angular velocity would be ω = 2π * 50 = 100π rad/s.
- Therefore, the correct answer is C, "100π rad/s".
Question 20:
A magnetic field is oriented from east to west. If a conductor is moved westward within this magnetic field, what can we say about the induced current?
Topic: Electromagnetic Induction
Correct Answer: C) Under these conditions, no induced current is produced
- The induced electromotive force (emf) in a moving conductor within a magnetic field is calculated using the equation Emf = VBLsinθ, where θ represents the angle between the motion of the conductor and the magnetic field.
- When the conductor moves in the same direction as the magnetic field (from east to west), the angle (θ) is 0 or 180 degrees. The sin(0) or sin(180) equals 0.
- Therefore, the induced emf, and consequently the induced current (since current = emf/resistance), is zero in this case. The correct answer is C, "Under these conditions, no induced current is produced".
Question 21:
Upon which fundamental principle is Lenz's Law of electromagnetism based?
Topic: Electromagnetic Induction
Correct Answer: A) Conservation of energy
- Lenz's Law, part of electromagnetic laws, is a reflection of the principle of conservation of energy.
- It states that the direction of induced current is such that it opposes the change causing it, ensuring no net energy is created or destroyed.
- Hence, the correct answer is A, "Conservation of energy".
MCQ 22:
Which component is typically absent in a direct current (DC) generator?
Topic: Direct Current Generators
Correct Answer: B) Slip rings
- A Direct Current (DC) generator typically consists of an Armature, Commutator, and Magnets.
- Slip rings are not a part of DC generators.
- Slip rings are often found in Alternating Current (AC) generators where they allow for continuous contact with the armature as it rotates, facilitating the generation of AC.
MCQ 23:
Where would you typically find a set of slip rings in action?
Topic: Generators
Correct Answer: A) In an AC generator
- Slip rings are electrical components that provide a means of making an electrical connection through a rotating assembly.
- They are crucial components in AC generators where they allow for continuous contact with the rotating armature, enabling the generation of alternating current.
MCQ 24:
Which of the following factors does not influence the induced electromotive force (emf) within a coil in the context of electromagnetic induction?
Topic: Electromagnetic Induction
Correct Answer: A) The resistance of the circuit
- Faraday's law of electromagnetic induction states that the induced emf is directly proportional to the rate of change of flux linkage.
- While the change in magnetic flux and the time taken for this change are key factors in determining the induced emf, the resistance of the circuit does not directly influence the induced emf in the coil.
Question 25:
Which of these assertions is accurate?
Topic: Electromagnetism
Correct Answer: A) A current is always accompanied by a magnetic field
- In electromagnetism, it is a well-known principle that a current flowing through a conductor will generate a magnetic field around it.
- However, the presence of a magnetic field does not necessarily indicate the existence of a current. A changing magnetic field is needed to induce a current.
- This implies that the correct answer is A, "A current is always accompanied by a magnetic field".
Question 26:
In a practical transformer, which of the following elements typically stays constant?
Topic: Transformers
Correct Answer: D) Frequency
- A practical transformer often modifies voltage levels, which in turn affects the current. This is due to the inverse relationship between voltage and current in a transformer.
- While the power output of an ideal transformer should match its input power, some energy loss usually occurs in real-world transformers, mainly due to joule heating and core hysteresis.
- Frequency, however, remains consistent in the transformation process. Therefore, the answer is D, "Frequency".
Question 27:
What is the standard unit for mutual inductance?
Topic: Electromagnetic Induction
Correct Answer: D) VsA-1
- Mutual inductance refers to the property of a conductor that quantifies its ability to induce an electromotive force in another conductor due to a change in current.
- The standard unit of mutual inductance is the henry (H), derived from the ratio of the induced voltage to the rate of change of current causing it.
- Following the definition, 1H equals 1Vs/A. Thus, the correct answer is D, "VsA-1".