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Q1. DC generator differs from AC generator mainly in the use of:
A DC generator uses a commutator (split ring) to convert alternating current produced in the coil into direct current. An AC generator uses slip rings, which allow the current to reverse direction naturally. This is the main difference between the two types of generators.
Q2. Momentary deflection in coil-2 occurs when current in coil-1 is:
A momentary deflection in coil-2 occurs when the current in coil-1 is changing. A changing current in coil-1 produces a changing magnetic field, which induces a current in coil-2. When the current becomes steady, the magnetic field stops changing, and the induced current disappears.
Q3. Slip rings in a generator are internally attached to the:
Slip rings in a generator are internally attached to the axle (shaft) of the rotating coil. The slip rings rotate with the coil, and the brushes press against them to collect the induced current. The axle connects the coil to the slip rings.
Q4. When both the coil and the magnet are stationary, the galvanometer shows:
When both the coil and the magnet are stationary, there is no change in magnetic flux through the coil. Since electromagnetic induction requires a changing magnetic field, no current is induced, and the galvanometer shows zero deflection.
Q5. Induced potential difference in a circuit sets up:
Induced potential difference (voltage) in a circuit sets up an electric current if the circuit is closed. The induced voltage drives the flow of charges, creating an electric current. This is the principle behind electric generators.
Q6. Most power stations generate:
Most power stations generate alternating current (AC) because AC is more efficient for long-distance transmission. AC voltage can be easily stepped up or down using transformers, reducing energy losses during transmission.
Q7. The polarity of induced current in an AC generator changes after:
In an AC generator, the polarity of induced current changes after every half rotation (180°) of the coil. This is because the coil moves through the magnetic field, and the direction of the induced current reverses when the coil passes through the vertical position.
Q8. Alternating current reverses its direction:
Alternating current (AC) reverses its direction periodically, meaning it changes direction at regular intervals. In India, AC changes direction 50 times per second (frequency 50 Hz). This periodic reversal is the defining characteristic of AC.
Q9. The function of brushes in a generator is to:
The function of brushes in a generator is to collect the induced current from the rotating slip rings (or commutator) and deliver it to the external circuit. The brushes are made of carbon and are stationary, pressing against the rotating rings.
Q10. Induced current can be produced by:
Induced current can be produced by changing the magnetic field around a conductor. This can be done by moving a magnet near a coil, moving a coil in a magnetic field, or changing the current in a nearby coil.
Q11. Change in magnetic field around a conductor induces:
A change in magnetic field around a conductor induces an electric current in the conductor (if the circuit is closed). This is electromagnetic induction. The induced current is caused by the induced potential difference (voltage).
Q12. The direction of induced current is given by:
Fleming’s right-hand rule is used to determine the direction of induced current in a conductor moving in a magnetic field. The thumb points in the direction of motion, the forefinger in the direction of the magnetic field, and the middle finger gives the direction of induced current.
Q13. For zero current, the galvanometer pointer remains at:
For zero current, the galvanometer pointer remains at the centre (zero mark). When current flows, the pointer deflects to the left or right depending on the direction of the current. The zero position indicates no current.
Q14. Motion of a magnet with respect to a coil produces:
Motion of a magnet with respect to a coil produces an induced potential difference (voltage) in the coil. This is due to the changing magnetic flux through the coil. If the circuit is closed, this induced potential difference causes an electric current to flow.
Q15. What is the principle of working of an electric generator?
An electric generator works on the principle of electromagnetic induction. When a coil rotates in a magnetic field, the magnetic flux through the coil changes, inducing an electric current. This converts mechanical energy into electrical energy.
Q16. The galvanometer deflects left or right depending on the:
The galvanometer deflects left or right depending on the direction of the current flowing through it. The direction of deflection tells us whether the current is flowing in one direction or the opposite direction.
Q17. In a DC generator, a _____ is used to obtain unidirectional current.
In a DC generator, a split-ring commutator is used to obtain unidirectional (direct) current. The commutator reverses the connection of the coil to the external circuit every half rotation, ensuring that the current always flows in the same direction.
Q18. Induced current is maximum when the motion of coil is:
Induced current is maximum when the motion of the coil is at right angles (perpendicular) to the magnetic field. The induced emf is given by e = Blv sin θ, and sin 90° = 1, giving the maximum value.
Q19. When the magnet and coil are stationary relative to each other, induced current is:
When the magnet and coil are stationary relative to each other, there is no change in magnetic flux, so the induced current is zero. Electromagnetic induction requires relative motion or a changing magnetic field.
Q20. If the south pole of the magnet is moved towards the coil, the galvanometer deflection is:
If the south pole of the magnet is moved towards the coil, the galvanometer deflection is opposite to what it was when the north pole was moved towards the coil. This is because the direction of the induced current depends on whether the magnetic flux is increasing or decreasing and which pole is moving.
Q21. AC changes direction after every:
In India, AC has a frequency of 50 Hz, meaning it completes 50 cycles per second. One cycle consists of two changes of direction, so AC changes direction 100 times per second—once every 1/100 second. Each half-cycle lasts 1/100 second.
Q22. In Fleming’s right-hand rule, the middle finger represents the direction of:
In Fleming’s right-hand rule, the middle finger represents the direction of induced current. The forefinger represents the magnetic field, and the thumb represents the direction of motion of the conductor.
Q23. Deflection in galvanometer indicates the presence of:
Deflection in a galvanometer indicates the presence of electric current. The galvanometer measures the current flowing through it. The amount of deflection shows the strength of the current.
Q24. Disconnecting coil-1 from the battery causes induced current in coil-2 in:
Disconnecting coil-1 from the battery causes the magnetic field to collapse. The induced current in coil-2 flows in the opposite direction to oppose the decrease in magnetic flux (Lenz’s law). When the current is switched on, the induced current is in the opposite direction.
Q25. Faraday discovered electromagnetic induction in the year:
Michael Faraday discovered electromagnetic induction in 1831. He found that a changing magnetic field induces an electric current in a conductor. This discovery is the principle behind electric generators and transformers.
Q26. In Fleming’s right-hand rule, the forefinger represents the direction of:
In Fleming’s right-hand rule, the forefinger represents the direction of the magnetic field. The thumb represents the direction of motion, and the middle finger represents the direction of induced current.
Q27. In India, the frequency of AC is:
In India, the frequency of alternating current (AC) is 50 Hz. This means the current changes direction 100 times per second (50 complete cycles per second). In the USA and some other countries, the frequency is 60 Hz.
Q28. Direct current always flows in:
Direct current (DC) always flows in one direction. The flow is unidirectional, meaning the current does not reverse its direction. Batteries and DC generators produce direct current.
Q29. The ends of the generator coil are connected to:
In an AC generator, the ends of the coil are connected to slip rings. In a DC generator, they are connected to a split-ring commutator. The slip rings or commutator allow the induced current to be collected by the brushes.
Q30. Coil-2 gets induced current due to changing magnetic field produced by:
Coil-2 gets induced current due to the changing magnetic field produced by coil-1 when the current in coil-1 changes. This is the principle of mutual induction. The changing current in coil-1 produces a changing magnetic field, which induces a current in coil-2.
Q31. A galvanometer can detect:
A galvanometer can detect the presence and direction of electric current. The deflection of the pointer indicates the current’s presence, and the direction of deflection indicates the direction of the current.
Q32. Fleming’s right-hand rule is used to determine the direction of:
Fleming’s right-hand rule is used to determine the direction of induced current when a conductor moves in a magnetic field. The thumb gives the direction of motion, the forefinger gives the field direction, and the middle finger gives the induced current direction.
Q33. In an electric generator, the rotating coil is placed between:
In an electric generator, the rotating coil is placed between two magnetic poles (north and south). The magnetic field from these poles interacts with the rotating coil to induce an electric current.
Q34. Electromagnetic induction was discovered by:
Electromagnetic induction was discovered by Michael Faraday in 1831. He demonstrated that a changing magnetic field produces an electric current in a conductor. This is one of the most important discoveries in physics.
Q35. In an AC generator, the current changes direction after every:
In an AC generator, the current changes direction after every half rotation (180°) of the coil. This is because the coil’s orientation relative to the magnetic field changes, and the direction of induced current reverses.
Q36. When current in coil-1 becomes steady, the galvanometer in coil-2 shows:
When current in coil-1 becomes steady, the magnetic field becomes constant, and there is no change in magnetic flux through coil-2. Therefore, the galvanometer in coil-2 shows no deflection. Induced current only occurs when the magnetic field is changing.
Q37. Changing current in a nearby coil produces current in another coil due to change in:
Changing current in a nearby coil produces current in another coil due to the change in the magnetic field. The changing current in the first coil produces a changing magnetic field, which induces a current in the second coil (mutual induction).
Q38. In Fleming’s right-hand rule, the thumb shows the direction of:
In Fleming’s right-hand rule, the thumb shows the direction of motion of the conductor. The forefinger shows the direction of the magnetic field, and the middle finger shows the direction of induced current.
Q39. What does an electric fuse do in a circuit based on the heating effect of current?
An electric fuse melts and breaks the circuit when the current exceeds a safe limit. It works on the heating effect of current—when excessive current flows, the fuse wire heats up and melts, breaking the circuit and protecting appliances from damage.
Q40. Electromagnetic induction is caused by:
Electromagnetic induction is caused by a changing magnetic field. A changing magnetic field induces an electric current in a conductor. A constant magnetic field does not induce any current.
Q41. When the coil is moved towards the north pole of the magnet, the galvanometer needle deflects:
Q42. An important advantage of AC over DC is:
An important advantage of AC over DC is efficient long-distance transmission. AC voltage can be stepped up using transformers, which reduces power losses during transmission. At the receiving end, it can be stepped down for use. DC cannot be easily transformed.
Q43. Current produced by an AC generator is called:
Current produced by an AC generator is called alternating current (AC). This is because the current changes direction periodically as the coil rotates in the magnetic field.
Q44. An electric generator works on the principle of:
An electric generator works on the principle of electromagnetic induction. When a coil rotates in a magnetic field, a changing magnetic flux induces an electric current in the coil. This converts mechanical energy into electrical energy.
Q45. An electric generator converts:
An electric generator converts mechanical energy (from a turbine, engine, or hand crank) into electrical energy. The mechanical rotation of the coil in a magnetic field induces an electric current.
Q46. Electric generators are used to produce electricity based on the principle discovered by:
Electric generators are used to produce electricity based on the principle of electromagnetic induction discovered by Michael Faraday. This discovery is the foundation of modern electricity generation.
Q47. When the coil is moved away from the magnet, the galvanometer needle deflects:
When the coil is moved away from the magnet, the galvanometer needle deflects in the opposite direction compared to when it is moved towards the magnet. This is because the direction of the induced current reverses when the motion is reversed.
Q48. The induced current depends on the direction of:
The induced current depends on the direction of both the magnetic field and the motion of the conductor. Reversing either one reverses the direction of the induced current. This is given by Fleming’s right-hand rule.
Q49. In a generator, larger number of turns in the coil results in:
In a generator, a larger number of turns in the coil results in a larger induced current. This is because the induced emf is proportional to the number of turns (e = -N dΦ/dt). More turns mean more induced voltage and current.
Q50. Electromagnetic induction requires:
Electromagnetic induction requires relative motion between a conductor and a magnetic field, or a changing magnetic field. A stationary conductor in a constant magnetic field does not produce any induced current. The change in magnetic flux is essential for induction.